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This is /home/wk/s/libgcrypt/doc/gcrypt.info, produced by makeinfo
version 4.13 from /home/wk/s/libgcrypt/doc/gcrypt.texi.
This manual is for Libgcrypt (version 1.6.1, 29 January 2014), which is
GNU's library of cryptographic building blocks.
Copyright (C) 2000, 2002, 2003, 2004, 2006, 2007, 2008, 2009, 2011,
2012 Free Software Foundation, Inc.
Copyright (C) 2012, 2013 g10 Code GmbH
Permission is granted to copy, distribute and/or modify this
document under the terms of the GNU General Public License as
published by the Free Software Foundation; either version 2 of the
License, or (at your option) any later version. The text of the
license can be found in the section entitled "GNU General Public
License".
INFO-DIR-SECTION GNU Libraries
START-INFO-DIR-ENTRY
* libgcrypt: (gcrypt). Cryptographic function library.
END-INFO-DIR-ENTRY

File: gcrypt.info, Node: Top, Next: Introduction, Up: (dir)
The Libgcrypt Library
*********************
This manual is for Libgcrypt (version 1.6.1, 29 January 2014), which is
GNU's library of cryptographic building blocks.
Copyright (C) 2000, 2002, 2003, 2004, 2006, 2007, 2008, 2009, 2011,
2012 Free Software Foundation, Inc.
Copyright (C) 2012, 2013 g10 Code GmbH
Permission is granted to copy, distribute and/or modify this
document under the terms of the GNU General Public License as
published by the Free Software Foundation; either version 2 of the
License, or (at your option) any later version. The text of the
license can be found in the section entitled "GNU General Public
License".
* Menu:
* Introduction:: What is Libgcrypt.
* Preparation:: What you should do before using the library.
* Generalities:: General library functions and data types.
* Handler Functions:: Working with handler functions.
* Symmetric cryptography:: How to use symmetric cryptography.
* Public Key cryptography:: How to use public key cryptography.
* Hashing:: How to use hash algorithms.
* Message Authentication Codes:: How to use MAC algorithms.
* Key Derivation:: How to derive keys from strings
* Random Numbers:: How to work with random numbers.
* S-expressions:: How to manage S-expressions.
* MPI library:: How to work with multi-precision-integers.
* Prime numbers:: How to use the Prime number related functions.
* Utilities:: Utility functions.
* Tools:: Utility tools
* Architecture:: How Libgcrypt works internally.
Appendices
* Self-Tests:: Description of the self-tests.
* FIPS Mode:: Description of the FIPS mode.
* Library Copying:: The GNU Lesser General Public License
says how you can copy and share Libgcrypt.
* Copying:: The GNU General Public License says how you
can copy and share some parts of Libgcrypt.
Indices
* Figures and Tables:: Index of figures and tables.
* Concept Index:: Index of concepts and programs.
* Function and Data Index:: Index of functions, variables and data types.

File: gcrypt.info, Node: Introduction, Next: Preparation, Prev: Top, Up: Top
1 Introduction
**************
Libgcrypt is a library providing cryptographic building blocks.
* Menu:
* Getting Started:: How to use this manual.
* Features:: A glance at Libgcrypt's features.
* Overview:: Overview about the library.

File: gcrypt.info, Node: Getting Started, Next: Features, Up: Introduction
1.1 Getting Started
===================
This manual documents the Libgcrypt library application programming
interface (API). All functions and data types provided by the library
are explained.
The reader is assumed to possess basic knowledge about applied
cryptography.
This manual can be used in several ways. If read from the beginning
to the end, it gives a good introduction into the library and how it
can be used in an application. Forward references are included where
necessary. Later on, the manual can be used as a reference manual to
get just the information needed about any particular interface of the
library. Experienced programmers might want to start looking at the
examples at the end of the manual, and then only read up those parts of
the interface which are unclear.

File: gcrypt.info, Node: Features, Next: Overview, Prev: Getting Started, Up: Introduction
1.2 Features
============
Libgcrypt might have a couple of advantages over other libraries doing
a similar job.
It's Free Software
Anybody can use, modify, and redistribute it under the terms of
the GNU Lesser General Public License (*note Library Copying::).
Note, that some parts (which are in general not needed by
applications) are subject to the terms of the GNU General Public
License (*note Copying::); please see the README file of the
distribution for of list of these parts.
It encapsulates the low level cryptography
Libgcrypt provides a high level interface to cryptographic
building blocks using an extensible and flexible API.

File: gcrypt.info, Node: Overview, Prev: Features, Up: Introduction
1.3 Overview
============
The Libgcrypt library is fully thread-safe, where it makes sense to be
thread-safe. Not thread-safe are some cryptographic functions that
modify a certain context stored in handles. If the user really intents
to use such functions from different threads on the same handle, he has
to take care of the serialization of such functions himself. If not
described otherwise, every function is thread-safe.
Libgcrypt depends on the library `libgpg-error', which contains
common error handling related code for GnuPG components.

File: gcrypt.info, Node: Preparation, Next: Generalities, Prev: Introduction, Up: Top
2 Preparation
*************
To use Libgcrypt, you have to perform some changes to your sources and
the build system. The necessary changes are small and explained in the
following sections. At the end of this chapter, it is described how
the library is initialized, and how the requirements of the library are
verified.
* Menu:
* Header:: What header file you need to include.
* Building sources:: How to build sources using the library.
* Building sources using Automake:: How to build sources with the help of Automake.
* Initializing the library:: How to initialize the library.
* Multi-Threading:: How Libgcrypt can be used in a MT environment.
* Enabling FIPS mode:: How to enable the FIPS mode.
* Hardware features:: How to disable hardware features.

File: gcrypt.info, Node: Header, Next: Building sources, Up: Preparation
2.1 Header
==========
All interfaces (data types and functions) of the library are defined in
the header file `gcrypt.h'. You must include this in all source files
using the library, either directly or through some other header file,
like this:
#include <gcrypt.h>
The name space of Libgcrypt is `gcry_*' for function and type names
and `GCRY*' for other symbols. In addition the same name prefixes with
one prepended underscore are reserved for internal use and should never
be used by an application. Note that Libgcrypt uses libgpg-error,
which uses `gpg_*' as name space for function and type names and
`GPG_*' for other symbols, including all the error codes.
Certain parts of gcrypt.h may be excluded by defining these macros:
`GCRYPT_NO_MPI_MACROS'
Do not define the shorthand macros `mpi_*' for `gcry_mpi_*'.
`GCRYPT_NO_DEPRECATED'
Do not include definitions for deprecated features. This is
useful to make sure that no deprecated features are used.

File: gcrypt.info, Node: Building sources, Next: Building sources using Automake, Prev: Header, Up: Preparation
2.2 Building sources
====================
If you want to compile a source file including the `gcrypt.h' header
file, you must make sure that the compiler can find it in the directory
hierarchy. This is accomplished by adding the path to the directory in
which the header file is located to the compilers include file search
path (via the `-I' option).
However, the path to the include file is determined at the time the
source is configured. To solve this problem, Libgcrypt ships with a
small helper program `libgcrypt-config' that knows the path to the
include file and other configuration options. The options that need to
be added to the compiler invocation at compile time are output by the
`--cflags' option to `libgcrypt-config'. The following example shows
how it can be used at the command line:
gcc -c foo.c `libgcrypt-config --cflags`
Adding the output of `libgcrypt-config --cflags' to the compilers
command line will ensure that the compiler can find the Libgcrypt header
file.
A similar problem occurs when linking the program with the library.
Again, the compiler has to find the library files. For this to work,
the path to the library files has to be added to the library search path
(via the `-L' option). For this, the option `--libs' to
`libgcrypt-config' can be used. For convenience, this option also
outputs all other options that are required to link the program with
the Libgcrypt libraries (in particular, the `-lgcrypt' option). The
example shows how to link `foo.o' with the Libgcrypt library to a
program `foo'.
gcc -o foo foo.o `libgcrypt-config --libs`
Of course you can also combine both examples to a single command by
specifying both options to `libgcrypt-config':
gcc -o foo foo.c `libgcrypt-config --cflags --libs`

File: gcrypt.info, Node: Building sources using Automake, Next: Initializing the library, Prev: Building sources, Up: Preparation
2.3 Building sources using Automake
===================================
It is much easier if you use GNU Automake instead of writing your own
Makefiles. If you do that, you do not have to worry about finding and
invoking the `libgcrypt-config' script at all. Libgcrypt provides an
extension to Automake that does all the work for you.
-- Macro: AM_PATH_LIBGCRYPT ([MINIMUM-VERSION], [ACTION-IF-FOUND],
[ACTION-IF-NOT-FOUND])
Check whether Libgcrypt (at least version MINIMUM-VERSION, if
given) exists on the host system. If it is found, execute
ACTION-IF-FOUND, otherwise do ACTION-IF-NOT-FOUND, if given.
Additionally, the function defines `LIBGCRYPT_CFLAGS' to the flags
needed for compilation of the program to find the `gcrypt.h'
header file, and `LIBGCRYPT_LIBS' to the linker flags needed to
link the program to the Libgcrypt library.
You can use the defined Autoconf variables like this in your
`Makefile.am':
AM_CPPFLAGS = $(LIBGCRYPT_CFLAGS)
LDADD = $(LIBGCRYPT_LIBS)

File: gcrypt.info, Node: Initializing the library, Next: Multi-Threading, Prev: Building sources using Automake, Up: Preparation
2.4 Initializing the library
============================
Before the library can be used, it must initialize itself. This is
achieved by invoking the function `gcry_check_version' described below.
Also, it is often desirable to check that the version of Libgcrypt
used is indeed one which fits all requirements. Even with binary
compatibility, new features may have been introduced, but due to
problem with the dynamic linker an old version may actually be used.
So you may want to check that the version is okay right after program
startup.
-- Function: const char * gcry_check_version (const char *REQ_VERSION)
The function `gcry_check_version' initializes some subsystems used
by Libgcrypt and must be invoked before any other function in the
library, with the exception of the `GCRYCTL_SET_THREAD_CBS' command
(called via the `gcry_control' function). *Note Multi-Threading::.
Furthermore, this function returns the version number of the
library. It can also verify that the version number is higher
than a certain required version number REQ_VERSION, if this value
is not a null pointer.
Libgcrypt uses a concept known as secure memory, which is a region of
memory set aside for storing sensitive data. Because such memory is a
scarce resource, it needs to be setup in advanced to a fixed size.
Further, most operating systems have special requirements on how that
secure memory can be used. For example, it might be required to install
an application as "setuid(root)" to allow allocating such memory.
Libgcrypt requires a sequence of initialization steps to make sure that
this works correctly. The following examples show the necessary steps.
If you don't have a need for secure memory, for example if your
application does not use secret keys or other confidential data or it
runs in a controlled environment where key material floating around in
memory is not a problem, you should initialize Libgcrypt this way:
/* Version check should be the very first call because it
makes sure that important subsystems are intialized. */
if (!gcry_check_version (GCRYPT_VERSION))
{
fputs ("libgcrypt version mismatch\n", stderr);
exit (2);
}
/* Disable secure memory. */
gcry_control (GCRYCTL_DISABLE_SECMEM, 0);
/* ... If required, other initialization goes here. */
/* Tell Libgcrypt that initialization has completed. */
gcry_control (GCRYCTL_INITIALIZATION_FINISHED, 0);
If you have to protect your keys or other information in memory
against being swapped out to disk and to enable an automatic overwrite
of used and freed memory, you need to initialize Libgcrypt this way:
/* Version check should be the very first call because it
makes sure that important subsystems are initialized. */
if (!gcry_check_version (GCRYPT_VERSION))
{
fputs ("libgcrypt version mismatch\n", stderr);
exit (2);
}
/* We don't want to see any warnings, e.g. because we have not yet
parsed program options which might be used to suppress such
warnings. */
gcry_control (GCRYCTL_SUSPEND_SECMEM_WARN);
/* ... If required, other initialization goes here. Note that the
process might still be running with increased privileges and that
the secure memory has not been initialized. */
/* Allocate a pool of 16k secure memory. This make the secure memory
available and also drops privileges where needed. */
gcry_control (GCRYCTL_INIT_SECMEM, 16384, 0);
/* It is now okay to let Libgcrypt complain when there was/is
a problem with the secure memory. */
gcry_control (GCRYCTL_RESUME_SECMEM_WARN);
/* ... If required, other initialization goes here. */
/* Tell Libgcrypt that initialization has completed. */
gcry_control (GCRYCTL_INITIALIZATION_FINISHED, 0);
It is important that these initialization steps are not done by a
library but by the actual application. A library using Libgcrypt might
want to check for finished initialization using:
if (!gcry_control (GCRYCTL_INITIALIZATION_FINISHED_P))
{
fputs ("libgcrypt has not been initialized\n", stderr);
abort ();
}
Instead of terminating the process, the library may instead print a
warning and try to initialize Libgcrypt itself. See also the section on
multi-threading below for more pitfalls.

File: gcrypt.info, Node: Multi-Threading, Next: Enabling FIPS mode, Prev: Initializing the library, Up: Preparation
2.5 Multi-Threading
===================
As mentioned earlier, the Libgcrypt library is thread-safe if you
adhere to the following requirements:
* If your application is multi-threaded, you must set the thread
support callbacks with the `GCRYCTL_SET_THREAD_CBS' command
*before* any other function in the library.
This is easy enough if you are indeed writing an application using
Libgcrypt. It is rather problematic if you are writing a library
instead. Here are some tips what to do if you are writing a
library:
If your library requires a certain thread package, just initialize
Libgcrypt to use this thread package. If your library supports
multiple thread packages, but needs to be configured, you will
have to implement a way to determine which thread package the
application wants to use with your library anyway. Then configure
Libgcrypt to use this thread package.
If your library is fully reentrant without any special support by a
thread package, then you are lucky indeed. Unfortunately, this
does not relieve you from doing either of the two above, or use a
third option. The third option is to let the application
initialize Libgcrypt for you. Then you are not using Libgcrypt
transparently, though.
As if this was not difficult enough, a conflict may arise if two
libraries try to initialize Libgcrypt independently of each
others, and both such libraries are then linked into the same
application. To make it a bit simpler for you, this will probably
work, but only if both libraries have the same requirement for the
thread package. This is currently only supported for the
non-threaded case, GNU Pth and pthread.
If you use pthread and your applications forks and does not
directly call exec (even calling stdio functions), all kind of
problems may occur. Future versions of Libgcrypt will try to
cleanup using pthread_atfork but even that may lead to problems.
This is a common problem with almost all applications using
pthread and fork.
Note that future versions of Libgcrypt will drop this flexible
thread support and instead only support the platforms standard
thread implementation.
* The function `gcry_check_version' must be called before any other
function in the library, except the `GCRYCTL_SET_THREAD_CBS'
command (called via the `gcry_control' function), because it
initializes the thread support subsystem in Libgcrypt. To achieve
this in multi-threaded programs, you must synchronize the memory
with respect to other threads that also want to use Libgcrypt.
For this, it is sufficient to call `gcry_check_version' before
creating the other threads using Libgcrypt(1).
* Just like the function `gpg_strerror', the function
`gcry_strerror' is not thread safe. You have to use
`gpg_strerror_r' instead.
Libgcrypt contains convenient macros, which define the necessary
thread callbacks for PThread and for GNU Pth:
`GCRY_THREAD_OPTION_PTH_IMPL'
This macro defines the following (static) symbols:
`gcry_pth_init', `gcry_pth_mutex_init', `gcry_pth_mutex_destroy',
`gcry_pth_mutex_lock', `gcry_pth_mutex_unlock', `gcry_pth_read',
`gcry_pth_write', `gcry_pth_select', `gcry_pth_waitpid',
`gcry_pth_accept', `gcry_pth_connect', `gcry_threads_pth'.
After including this macro, `gcry_control()' shall be used with a
command of `GCRYCTL_SET_THREAD_CBS' in order to register the
thread callback structure named "gcry_threads_pth". Example:
ret = gcry_control (GCRYCTL_SET_THREAD_CBS, &gcry_threads_pth);
`GCRY_THREAD_OPTION_PTHREAD_IMPL'
This macro defines the following (static) symbols:
`gcry_pthread_mutex_init', `gcry_pthread_mutex_destroy',
`gcry_pthread_mutex_lock', `gcry_pthread_mutex_unlock',
`gcry_threads_pthread'.
After including this macro, `gcry_control()' shall be used with a
command of `GCRYCTL_SET_THREAD_CBS' in order to register the
thread callback structure named "gcry_threads_pthread". Example:
ret = gcry_control (GCRYCTL_SET_THREAD_CBS, &gcry_threads_pthread);
Note that these macros need to be terminated with a semicolon. Keep
in mind that these are convenient macros for C programmers; C++
programmers might have to wrap these macros in an "extern C" body.
---------- Footnotes ----------
(1) At least this is true for POSIX threads, as `pthread_create' is
a function that synchronizes memory with respects to other threads.
There are many functions which have this property, a complete list can
be found in POSIX, IEEE Std 1003.1-2003, Base Definitions, Issue 6, in
the definition of the term "Memory Synchronization". For other thread
packages, more relaxed or more strict rules may apply.

File: gcrypt.info, Node: Enabling FIPS mode, Next: Hardware features, Prev: Multi-Threading, Up: Preparation
2.6 How to enable the FIPS mode
===============================
Libgcrypt may be used in a FIPS 140-2 mode. Note, that this does not
necessary mean that Libcgrypt is an appoved FIPS 140-2 module. Check
the NIST database at `http://csrc.nist.gov/groups/STM/cmvp/' to see what
versions of Libgcrypt are approved.
Because FIPS 140 has certain restrictions on the use of cryptography
which are not always wanted, Libgcrypt needs to be put into FIPS mode
explicitly. Three alternative mechanisms are provided to switch
Libgcrypt into this mode:
* If the file `/proc/sys/crypto/fips_enabled' exists and contains a
numeric value other than `0', Libgcrypt is put into FIPS mode at
initialization time. Obviously this works only on systems with a
`proc' file system (i.e. GNU/Linux).
* If the file `/etc/gcrypt/fips_enabled' exists, Libgcrypt is put
into FIPS mode at initialization time. Note that this filename is
hardwired and does not depend on any configuration options.
* If the application requests FIPS mode using the control command
`GCRYCTL_FORCE_FIPS_MODE'. This must be done prior to any
initialization (i.e. before `gcry_check_version').
In addition to the standard FIPS mode, Libgcrypt may also be put into
an Enforced FIPS mode by writing a non-zero value into the file
`/etc/gcrypt/fips_enabled' or by using the control command
`GCRYCTL_SET_ENFORCED_FIPS_FLAG' before any other calls to libgcrypt.
The Enforced FIPS mode helps to detect applications which don't fulfill
all requirements for using Libgcrypt in FIPS mode (*note FIPS Mode::).
Once Libgcrypt has been put into FIPS mode, it is not possible to
switch back to standard mode without terminating the process first. If
the logging verbosity level of Libgcrypt has been set to at least 2,
the state transitions and the self-tests are logged.

File: gcrypt.info, Node: Hardware features, Prev: Enabling FIPS mode, Up: Preparation
2.7 How to disable hardware features
====================================
Libgcrypt makes use of certain hardware features. If the use of a
feature is not desired it may be either be disabled by a program or
globally using a configuration file. The currently supported features
are
`padlock-rng'
`padlock-aes'
`padlock-sha'
`padlock-mmul'
`intel-cpu'
`intel-bmi2'
`intel-ssse3'
`intel-pclmul'
`intel-aesni'
`intel-rdrand'
`intel-avx'
`intel-avx2'
`arm-neon'
To disable a feature for all processes using Libgcrypt 1.6 or newer,
create the file `/etc/gcrypt/hwf.deny' and put each feature not to be
used on a single line. Empty lines, white space, and lines prefixed
with a hash mark are ignored. The file should be world readable.
To disable a feature specifically for a program that program must
tell it Libgcrypt before before calling `gcry_check_version'.
Example:(1)
gcry_control (GCRYCTL_DISABLE_HWF, "intel-rdrand", NULL);
To print the list of active features you may use this command:
mpicalc --print-config | grep ^hwflist: | tr : '\n' | tail -n +2
---------- Footnotes ----------
(1) NB. Libgcrypt uses the RDRAND feature only as one source of
entropy. A CPU with a broken RDRAND will thus not compromise of the
random number generator

File: gcrypt.info, Node: Generalities, Next: Handler Functions, Prev: Preparation, Up: Top
3 Generalities
**************
* Menu:
* Controlling the library:: Controlling Libgcrypt's behavior.
* Error Handling:: Error codes and such.

File: gcrypt.info, Node: Controlling the library, Next: Error Handling, Up: Generalities
3.1 Controlling the library
===========================
-- Function: gcry_error_t gcry_control (enum gcry_ctl_cmds CMD, ...)
This function can be used to influence the general behavior of
Libgcrypt in several ways. Depending on CMD, more arguments can
or have to be provided.
`GCRYCTL_ENABLE_M_GUARD; Arguments: none'
This command enables the built-in memory guard. It must not
be used to activate the memory guard after the memory
management has already been used; therefore it can ONLY be
used before `gcry_check_version'. Note that the memory guard
is NOT used when the user of the library has set his own
memory management callbacks.
`GCRYCTL_ENABLE_QUICK_RANDOM; Arguments: none'
This command inhibits the use the very secure random quality
level (`GCRY_VERY_STRONG_RANDOM') and degrades all request
down to `GCRY_STRONG_RANDOM'. In general this is not
recommended. However, for some applications the extra
quality random Libgcrypt tries to create is not justified and
this option may help to get better performance. Please check
with a crypto expert whether this option can be used for your
application.
This option can only be used at initialization time.
`GCRYCTL_DUMP_RANDOM_STATS; Arguments: none'
This command dumps random number generator related statistics
to the library's logging stream.
`GCRYCTL_DUMP_MEMORY_STATS; Arguments: none'
This command dumps memory management related statistics to
the library's logging stream.
`GCRYCTL_DUMP_SECMEM_STATS; Arguments: none'
This command dumps secure memory management related
statistics to the library's logging stream.
`GCRYCTL_DROP_PRIVS; Arguments: none'
This command disables the use of secure memory and drops the
privileges of the current process. This command has not much
use; the suggested way to disable secure memory is to use
`GCRYCTL_DISABLE_SECMEM' right after initialization.
`GCRYCTL_DISABLE_SECMEM; Arguments: none'
This command disables the use of secure memory. If this
command is used in FIPS mode, FIPS mode will be disabled and
the function `gcry_fips_mode_active' returns false. However,
in Enforced FIPS mode this command has no effect at all.
Many applications do not require secure memory, so they
should disable it right away. This command should be
executed right after `gcry_check_version'.
`GCRYCTL_DISABLE_LOCKED_SECMEM; Arguments: none'
This command disables the use of the mlock call for secure
memory. Disabling the use of mlock may for example be done
if an encrypted swap space is in use. This command should be
executed right after `gcry_check_version'.
`GCRYCTL_DISABLE_PRIV_DROP; Arguments: none'
This command sets a global flag to tell the secure memory
subsystem that it shall not drop privileges after secure
memory has been allocated. This command is commonly used
right after `gcry_check_version' but may also be used right
away at program startup. It won't have an effect after the
secure memory pool has been initialized. WARNING: A process
running setuid(root) is a severe security risk. Processes
making use of Libgcrypt or other complex code should drop
these extra privileges as soon as possible. If this command
has been used the caller is responsible for dropping the
privileges.
`GCRYCTL_INIT_SECMEM; Arguments: int nbytes'
This command is used to allocate a pool of secure memory and
thus enabling the use of secure memory. It also drops all
extra privileges the process has (i.e. if it is run as setuid
(root)). If the argument NBYTES is 0, secure memory will be
disabled. The minimum amount of secure memory allocated is
currently 16384 bytes; you may thus use a value of 1 to
request that default size.
`GCRYCTL_TERM_SECMEM; Arguments: none'
This command zeroises the secure memory and destroys the
handler. The secure memory pool may not be used anymore
after running this command. If the secure memory pool as
already been destroyed, this command has no effect.
Applications might want to run this command from their exit
handler to make sure that the secure memory gets properly
destroyed. This command is not necessarily thread-safe but
that should not be needed in cleanup code. It may be called
from a signal handler.
`GCRYCTL_DISABLE_SECMEM_WARN; Arguments: none'
Disable warning messages about problems with the secure memory
subsystem. This command should be run right after
`gcry_check_version'.
`GCRYCTL_SUSPEND_SECMEM_WARN; Arguments: none'
Postpone warning messages from the secure memory subsystem.
*Note the initialization example: sample-use-suspend-secmem,
on how to use it.
`GCRYCTL_RESUME_SECMEM_WARN; Arguments: none'
Resume warning messages from the secure memory subsystem.
*Note the initialization example: sample-use-resume-secmem,
on how to use it.
`GCRYCTL_USE_SECURE_RNDPOOL; Arguments: none'
This command tells the PRNG to store random numbers in secure
memory. This command should be run right after
`gcry_check_version' and not later than the command
GCRYCTL_INIT_SECMEM. Note that in FIPS mode the secure
memory is always used.
`GCRYCTL_SET_RANDOM_SEED_FILE; Arguments: const char *filename'
This command specifies the file, which is to be used as seed
file for the PRNG. If the seed file is registered prior to
initialization of the PRNG, the seed file's content (if it
exists and seems to be valid) is fed into the PRNG pool.
After the seed file has been registered, the PRNG can be
signalled to write out the PRNG pool's content into the seed
file with the following command.
`GCRYCTL_UPDATE_RANDOM_SEED_FILE; Arguments: none'
Write out the PRNG pool's content into the registered seed
file.
Multiple instances of the applications sharing the same
random seed file can be started in parallel, in which case
they will read out the same pool and then race for updating
it (the last update overwrites earlier updates). They will
differentiate only by the weak entropy that is added in
read_seed_file based on the PID and clock, and up to 16 bytes
of weak random non-blockingly. The consequence is that the
output of these different instances is correlated to some
extent. In a perfect attack scenario, the attacker can
control (or at least guess) the PID and clock of the
application, and drain the system's entropy pool to reduce
the "up to 16 bytes" above to 0. Then the dependencies of the
initial states of the pools are completely known. Note that
this is not an issue if random of `GCRY_VERY_STRONG_RANDOM'
quality is requested as in this case enough extra entropy
gets mixed. It is also not an issue when using Linux
(rndlinux driver), because this one guarantees to read full
16 bytes from /dev/urandom and thus there is no way for an
attacker without kernel access to control these 16 bytes.
`GCRYCTL_CLOSE_RANDOM_DEVICE; Arguments: none'
Try to close the random device. If on Unix system you call
fork(), the child process does no call exec(), and you do not
intend to use Libgcrypt in the child, it might be useful to
use this control code to close the inherited file descriptors
of the random device. If Libgcrypt is later used again by
the child, the device will be re-opened. On non-Unix systems
this control code is ignored.
`GCRYCTL_SET_VERBOSITY; Arguments: int level'
This command sets the verbosity of the logging. A level of 0
disables all extra logging whereas positive numbers enable
more verbose logging. The level may be changed at any time
but be aware that no memory synchronization is done so the
effect of this command might not immediately show up in other
threads. This command may even be used prior to
`gcry_check_version'.
`GCRYCTL_SET_DEBUG_FLAGS; Arguments: unsigned int flags'
Set the debug flag bits as given by the argument. Be aware
that that no memory synchronization is done so the effect of
this command might not immediately show up in other threads.
The debug flags are not considered part of the API and thus
may change without notice. As of now bit 0 enables debugging
of cipher functions and bit 1 debugging of
multi-precision-integers. This command may even be used
prior to `gcry_check_version'.
`GCRYCTL_CLEAR_DEBUG_FLAGS; Arguments: unsigned int flags'
Set the debug flag bits as given by the argument. Be aware
that that no memory synchronization is done so the effect of
this command might not immediately show up in other threads.
This command may even be used prior to `gcry_check_version'.
`GCRYCTL_DISABLE_INTERNAL_LOCKING; Arguments: none'
This command does nothing. It exists only for backward
compatibility.
`GCRYCTL_ANY_INITIALIZATION_P; Arguments: none'
This command returns true if the library has been basically
initialized. Such a basic initialization happens implicitly
with many commands to get certain internal subsystems
running. The common and suggested way to do this basic
initialization is by calling gcry_check_version.
`GCRYCTL_INITIALIZATION_FINISHED; Arguments: none'
This command tells the library that the application has
finished the initialization.
`GCRYCTL_INITIALIZATION_FINISHED_P; Arguments: none'
This command returns true if the command
GCRYCTL_INITIALIZATION_FINISHED has already been run.
`GCRYCTL_SET_THREAD_CBS; Arguments: struct ath_ops *ath_ops'
This command registers a thread-callback structure. *Note
Multi-Threading::.
`GCRYCTL_FAST_POLL; Arguments: none'
Run a fast random poll.
`GCRYCTL_SET_RNDEGD_SOCKET; Arguments: const char *filename'
This command may be used to override the default name of the
EGD socket to connect to. It may be used only during
initialization as it is not thread safe. Changing the socket
name again is not supported. The function may return an
error if the given filename is too long for a local socket
name.
EGD is an alternative random gatherer, used only on systems
lacking a proper random device.
`GCRYCTL_PRINT_CONFIG; Arguments: FILE *stream'
This command dumps information pertaining to the
configuration of the library to the given stream. If NULL is
given for STREAM, the log system is used. This command may
be used before the initialization has been finished but not
before a `gcry_check_version'.
`GCRYCTL_OPERATIONAL_P; Arguments: none'
This command returns true if the library is in an operational
state. This information makes only sense in FIPS mode. In
contrast to other functions, this is a pure test function and
won't put the library into FIPS mode or change the internal
state. This command may be used before the initialization
has been finished but not before a `gcry_check_version'.
`GCRYCTL_FIPS_MODE_P; Arguments: none'
This command returns true if the library is in FIPS mode.
Note, that this is no indication about the current state of
the library. This command may be used before the
initialization has been finished but not before a
`gcry_check_version'. An application may use this command or
the convenience macro below to check whether FIPS mode is
actually active.
-- Function: int gcry_fips_mode_active (void)
Returns true if the FIPS mode is active. Note that this
is implemented as a macro.
`GCRYCTL_FORCE_FIPS_MODE; Arguments: none'
Running this command puts the library into FIPS mode. If the
library is already in FIPS mode, a self-test is triggered and
thus the library will be put into operational state. This
command may be used before a call to `gcry_check_version' and
that is actually the recommended way to let an application
switch the library into FIPS mode. Note that Libgcrypt will
reject an attempt to switch to fips mode during or after the
initialization.
`GCRYCTL_SET_ENFORCED_FIPS_FLAG; Arguments: none'
Running this command sets the internal flag that puts the
library into the enforced FIPS mode during the FIPS mode
initialization. This command does not affect the library if
the library is not put into the FIPS mode and it must be used
before any other libgcrypt library calls that initialize the
library such as `gcry_check_version'. Note that Libgcrypt will
reject an attempt to switch to the enforced fips mode during
or after the initialization.
`GCRYCTL_SET_PREFERRED_RNG_TYPE; Arguments: int'
These are advisory commands to select a certain random number
generator. They are only advisory because libraries may not
know what an application actually wants or vice versa. Thus
Libgcrypt employs a priority check to select the actually
used RNG. If an applications selects a lower priority RNG
but a library requests a higher priority RNG Libgcrypt will
switch to the higher priority RNG. Applications and
libraries should use these control codes before
`gcry_check_version'. The available generators are:
`GCRY_RNG_TYPE_STANDARD'
A conservative standard generator based on the
"Continuously Seeded Pseudo Random Number Generator"
designed by Peter Gutmann.
`GCRY_RNG_TYPE_FIPS'
A deterministic random number generator conforming to he
document "NIST-Recommended Random Number Generator Based
on ANSI X9.31 Appendix A.2.4 Using the 3-Key Triple DES
and AES Algorithms" (2005-01-31). This implementation
uses the AES variant.
`GCRY_RNG_TYPE_SYSTEM'
A wrapper around the system's native RNG. On Unix
system these are usually the /dev/random and
/dev/urandom devices.
The default is `GCRY_RNG_TYPE_STANDARD' unless FIPS mode as
been enabled; in which case `GCRY_RNG_TYPE_FIPS' is used and
locked against further changes.
`GCRYCTL_GETT_CURRENT_RNG_TYPE; Arguments: int *'
This command stores the type of the currently used RNG as an
integer value at the provided address.
`GCRYCTL_SELFTEST; Arguments: none'
This may be used at anytime to have the library run all
implemented self-tests. It works in standard and in FIPS
mode. Returns 0 on success or an error code on failure.
`GCRYCTL_DISABLE_HWF; Arguments: const char *name'
Libgcrypt detects certain features of the CPU at startup
time. For performance tests it is sometimes required not to
use such a feature. This option may be used to disable a
certain feature; i.e. Libgcrypt behaves as if this feature
has not been detected. Note that the detection code might be
run if the feature has been disabled. This command must be
used at initialization time; i.e. before calling
`gcry_check_version'.

File: gcrypt.info, Node: Error Handling, Prev: Controlling the library, Up: Generalities
3.2 Error Handling
==================
Many functions in Libgcrypt can return an error if they fail. For this
reason, the application should always catch the error condition and
take appropriate measures, for example by releasing the resources and
passing the error up to the caller, or by displaying a descriptive
message to the user and cancelling the operation.
Some error values do not indicate a system error or an error in the
operation, but the result of an operation that failed properly. For
example, if you try to decrypt a tempered message, the decryption will
fail. Another error value actually means that the end of a data buffer
or list has been reached. The following descriptions explain for many
error codes what they mean usually. Some error values have specific
meanings if returned by a certain functions. Such cases are described
in the documentation of those functions.
Libgcrypt uses the `libgpg-error' library. This allows to share the
error codes with other components of the GnuPG system, and to pass
error values transparently from the crypto engine, or some helper
application of the crypto engine, to the user. This way no information
is lost. As a consequence, Libgcrypt does not use its own identifiers
for error codes, but uses those provided by `libgpg-error'. They
usually start with `GPG_ERR_'.
However, Libgcrypt does provide aliases for the functions defined in
libgpg-error, which might be preferred for name space consistency.
Most functions in Libgcrypt return an error code in the case of
failure. For this reason, the application should always catch the
error condition and take appropriate measures, for example by releasing
the resources and passing the error up to the caller, or by displaying
a descriptive message to the user and canceling the operation.
Some error values do not indicate a system error or an error in the
operation, but the result of an operation that failed properly.
GnuPG components, including Libgcrypt, use an extra library named
libgpg-error to provide a common error handling scheme. For more
information on libgpg-error, see the according manual.
* Menu:
* Error Values:: The error value and what it means.
* Error Sources:: A list of important error sources.
* Error Codes:: A list of important error codes.
* Error Strings:: How to get a descriptive string from a value.

File: gcrypt.info, Node: Error Values, Next: Error Sources, Up: Error Handling
3.2.1 Error Values
------------------
-- Data type: gcry_err_code_t
The `gcry_err_code_t' type is an alias for the `libgpg-error' type
`gpg_err_code_t'. The error code indicates the type of an error,
or the reason why an operation failed.
A list of important error codes can be found in the next section.
-- Data type: gcry_err_source_t
The `gcry_err_source_t' type is an alias for the `libgpg-error'
type `gpg_err_source_t'. The error source has not a precisely
defined meaning. Sometimes it is the place where the error
happened, sometimes it is the place where an error was encoded
into an error value. Usually the error source will give an
indication to where to look for the problem. This is not always
true, but it is attempted to achieve this goal.
A list of important error sources can be found in the next section.
-- Data type: gcry_error_t
The `gcry_error_t' type is an alias for the `libgpg-error' type
`gpg_error_t'. An error value like this has always two
components, an error code and an error source. Both together form
the error value.
Thus, the error value can not be directly compared against an error
code, but the accessor functions described below must be used.
However, it is guaranteed that only 0 is used to indicate success
(`GPG_ERR_NO_ERROR'), and that in this case all other parts of the
error value are set to 0, too.
Note that in Libgcrypt, the error source is used purely for
diagnostic purposes. Only the error code should be checked to test
for a certain outcome of a function. The manual only documents the
error code part of an error value. The error source is left
unspecified and might be anything.
-- Function: gcry_err_code_t gcry_err_code (gcry_error_t ERR)
The static inline function `gcry_err_code' returns the
`gcry_err_code_t' component of the error value ERR. This function
must be used to extract the error code from an error value in
order to compare it with the `GPG_ERR_*' error code macros.
-- Function: gcry_err_source_t gcry_err_source (gcry_error_t ERR)
The static inline function `gcry_err_source' returns the
`gcry_err_source_t' component of the error value ERR. This
function must be used to extract the error source from an error
value in order to compare it with the `GPG_ERR_SOURCE_*' error
source macros.
-- Function: gcry_error_t gcry_err_make (gcry_err_source_t SOURCE,
gcry_err_code_t CODE)
The static inline function `gcry_err_make' returns the error value
consisting of the error source SOURCE and the error code CODE.
This function can be used in callback functions to construct an
error value to return it to the library.
-- Function: gcry_error_t gcry_error (gcry_err_code_t CODE)
The static inline function `gcry_error' returns the error value
consisting of the default error source and the error code CODE.
For GCRY applications, the default error source is
`GPG_ERR_SOURCE_USER_1'. You can define `GCRY_ERR_SOURCE_DEFAULT'
before including `gcrypt.h' to change this default.
This function can be used in callback functions to construct an
error value to return it to the library.
The `libgpg-error' library provides error codes for all system error
numbers it knows about. If ERR is an unknown error number, the error
code `GPG_ERR_UNKNOWN_ERRNO' is used. The following functions can be
used to construct error values from system errno numbers.
-- Function: gcry_error_t gcry_err_make_from_errno
(gcry_err_source_t SOURCE, int ERR)
The function `gcry_err_make_from_errno' is like `gcry_err_make',
but it takes a system error like `errno' instead of a
`gcry_err_code_t' error code.
-- Function: gcry_error_t gcry_error_from_errno (int ERR)
The function `gcry_error_from_errno' is like `gcry_error', but it
takes a system error like `errno' instead of a `gcry_err_code_t'
error code.
Sometimes you might want to map system error numbers to error codes
directly, or map an error code representing a system error back to the
system error number. The following functions can be used to do that.
-- Function: gcry_err_code_t gcry_err_code_from_errno (int ERR)
The function `gcry_err_code_from_errno' returns the error code for
the system error ERR. If ERR is not a known system error, the
function returns `GPG_ERR_UNKNOWN_ERRNO'.
-- Function: int gcry_err_code_to_errno (gcry_err_code_t ERR)
The function `gcry_err_code_to_errno' returns the system error for
the error code ERR. If ERR is not an error code representing a
system error, or if this system error is not defined on this
system, the function returns `0'.

File: gcrypt.info, Node: Error Sources, Next: Error Codes, Prev: Error Values, Up: Error Handling
3.2.2 Error Sources
-------------------
The library `libgpg-error' defines an error source for every component
of the GnuPG system. The error source part of an error value is not
well defined. As such it is mainly useful to improve the diagnostic
error message for the user.
If the error code part of an error value is `0', the whole error
value will be `0'. In this case the error source part is of course
`GPG_ERR_SOURCE_UNKNOWN'.
The list of error sources that might occur in applications using
Libgcrypt is:
`GPG_ERR_SOURCE_UNKNOWN'
The error source is not known. The value of this error source is
`0'.
`GPG_ERR_SOURCE_GPGME'
The error source is GPGME itself.
`GPG_ERR_SOURCE_GPG'
The error source is GnuPG, which is the crypto engine used for the
OpenPGP protocol.
`GPG_ERR_SOURCE_GPGSM'
The error source is GPGSM, which is the crypto engine used for the
OpenPGP protocol.
`GPG_ERR_SOURCE_GCRYPT'
The error source is `libgcrypt', which is used by crypto engines
to perform cryptographic operations.
`GPG_ERR_SOURCE_GPGAGENT'
The error source is `gpg-agent', which is used by crypto engines
to perform operations with the secret key.
`GPG_ERR_SOURCE_PINENTRY'
The error source is `pinentry', which is used by `gpg-agent' to
query the passphrase to unlock a secret key.
`GPG_ERR_SOURCE_SCD'
The error source is the SmartCard Daemon, which is used by
`gpg-agent' to delegate operations with the secret key to a
SmartCard.
`GPG_ERR_SOURCE_KEYBOX'
The error source is `libkbx', a library used by the crypto engines
to manage local keyrings.
`GPG_ERR_SOURCE_USER_1'
`GPG_ERR_SOURCE_USER_2'
`GPG_ERR_SOURCE_USER_3'
`GPG_ERR_SOURCE_USER_4'
These error sources are not used by any GnuPG component and can be
used by other software. For example, applications using Libgcrypt
can use them to mark error values coming from callback handlers.
Thus `GPG_ERR_SOURCE_USER_1' is the default for errors created
with `gcry_error' and `gcry_error_from_errno', unless you define
`GCRY_ERR_SOURCE_DEFAULT' before including `gcrypt.h'.

File: gcrypt.info, Node: Error Codes, Next: Error Strings, Prev: Error Sources, Up: Error Handling
3.2.3 Error Codes
-----------------
The library `libgpg-error' defines many error values. The following
list includes the most important error codes.
`GPG_ERR_EOF'
This value indicates the end of a list, buffer or file.
`GPG_ERR_NO_ERROR'
This value indicates success. The value of this error code is
`0'. Also, it is guaranteed that an error value made from the
error code `0' will be `0' itself (as a whole). This means that
the error source information is lost for this error code, however,
as this error code indicates that no error occurred, this is
generally not a problem.
`GPG_ERR_GENERAL'
This value means that something went wrong, but either there is not
enough information about the problem to return a more useful error
value, or there is no separate error value for this type of
problem.
`GPG_ERR_ENOMEM'
This value means that an out-of-memory condition occurred.
`GPG_ERR_E...'
System errors are mapped to GPG_ERR_EFOO where FOO is the symbol
for the system error.
`GPG_ERR_INV_VALUE'
This value means that some user provided data was out of range.
`GPG_ERR_UNUSABLE_PUBKEY'
This value means that some recipients for a message were invalid.
`GPG_ERR_UNUSABLE_SECKEY'
This value means that some signers were invalid.
`GPG_ERR_NO_DATA'
This value means that data was expected where no data was found.
`GPG_ERR_CONFLICT'
This value means that a conflict of some sort occurred.
`GPG_ERR_NOT_IMPLEMENTED'
This value indicates that the specific function (or operation) is
not implemented. This error should never happen. It can only
occur if you use certain values or configuration options which do
not work, but for which we think that they should work at some
later time.
`GPG_ERR_DECRYPT_FAILED'
This value indicates that a decryption operation was unsuccessful.
`GPG_ERR_WRONG_KEY_USAGE'
This value indicates that a key is not used appropriately.
`GPG_ERR_NO_SECKEY'
This value indicates that no secret key for the user ID is
available.
`GPG_ERR_UNSUPPORTED_ALGORITHM'
This value means a verification failed because the cryptographic
algorithm is not supported by the crypto backend.
`GPG_ERR_BAD_SIGNATURE'
This value means a verification failed because the signature is
bad.
`GPG_ERR_NO_PUBKEY'
This value means a verification failed because the public key is
not available.
`GPG_ERR_NOT_OPERATIONAL'
This value means that the library is not yet in state which allows
to use this function. This error code is in particular returned if
Libgcrypt is operated in FIPS mode and the internal state of the
library does not yet or not anymore allow the use of a service.
This error code is only available with newer libgpg-error
versions, thus you might see "invalid error code" when passing
this to `gpg_strerror'. The numeric value of this error code is
176.
`GPG_ERR_USER_1'
`GPG_ERR_USER_2'
`...'
`GPG_ERR_USER_16'
These error codes are not used by any GnuPG component and can be
freely used by other software. Applications using Libgcrypt might
use them to mark specific errors returned by callback handlers if
no suitable error codes (including the system errors) for these
errors exist already.

File: gcrypt.info, Node: Error Strings, Prev: Error Codes, Up: Error Handling
3.2.4 Error Strings
-------------------
-- Function: const char * gcry_strerror (gcry_error_t ERR)
The function `gcry_strerror' returns a pointer to a statically
allocated string containing a description of the error code
contained in the error value ERR. This string can be used to
output a diagnostic message to the user.
-- Function: const char * gcry_strsource (gcry_error_t ERR)
The function `gcry_strsource' returns a pointer to a statically
allocated string containing a description of the error source
contained in the error value ERR. This string can be used to
output a diagnostic message to the user.
The following example illustrates the use of the functions described
above:
{
gcry_cipher_hd_t handle;
gcry_error_t err = 0;
err = gcry_cipher_open (&handle, GCRY_CIPHER_AES,
GCRY_CIPHER_MODE_CBC, 0);
if (err)
{
fprintf (stderr, "Failure: %s/%s\n",
gcry_strsource (err),
gcry_strerror (err));
}
}

File: gcrypt.info, Node: Handler Functions, Next: Symmetric cryptography, Prev: Generalities, Up: Top
4 Handler Functions
*******************
Libgcrypt makes it possible to install so called `handler functions',
which get called by Libgcrypt in case of certain events.
* Menu:
* Progress handler:: Using a progress handler function.
* Allocation handler:: Using special memory allocation functions.
* Error handler:: Using error handler functions.
* Logging handler:: Using a special logging function.

File: gcrypt.info, Node: Progress handler, Next: Allocation handler, Up: Handler Functions
4.1 Progress handler
====================
It is often useful to retrieve some feedback while long running
operations are performed.
-- Data type: gcry_handler_progress_t
Progress handler functions have to be of the type
`gcry_handler_progress_t', which is defined as:
`void (*gcry_handler_progress_t) (void *, const char *, int, int,
int)'
The following function may be used to register a handler function for
this purpose.
-- Function: void gcry_set_progress_handler (gcry_handler_progress_t
CB, void *CB_DATA)
This function installs CB as the `Progress handler' function. It
may be used only during initialization. CB must be defined as
follows:
void
my_progress_handler (void *CB_DATA, const char *WHAT,
int PRINTCHAR, int CURRENT, int TOTAL)
{
/* Do something. */
}
A description of the arguments of the progress handler function
follows.
CB_DATA
The argument provided in the call to
`gcry_set_progress_handler'.
WHAT
A string identifying the type of the progress output. The
following values for WHAT are defined:
`need_entropy'
Not enough entropy is available. TOTAL holds the number
of required bytes.
`wait_dev_random'
Waiting to re-open a random device. TOTAL gives the
number of seconds until the next try.
`primegen'
Values for PRINTCHAR:
`\n'
Prime generated.
`!'
Need to refresh the pool of prime numbers.
`<, >'
Number of bits adjusted.
`^'
Searching for a generator.
`.'
Fermat test on 10 candidates failed.
`:'
Restart with a new random value.
`+'
Rabin Miller test passed.

File: gcrypt.info, Node: Allocation handler, Next: Error handler, Prev: Progress handler, Up: Handler Functions
4.2 Allocation handler
======================
It is possible to make Libgcrypt use special memory allocation
functions instead of the built-in ones.
Memory allocation functions are of the following types:
-- Data type: gcry_handler_alloc_t
This type is defined as: `void *(*gcry_handler_alloc_t) (size_t
n)'.
-- Data type: gcry_handler_secure_check_t
This type is defined as: `int *(*gcry_handler_secure_check_t)
(const void *)'.
-- Data type: gcry_handler_realloc_t
This type is defined as: `void *(*gcry_handler_realloc_t) (void
*p, size_t n)'.
-- Data type: gcry_handler_free_t
This type is defined as: `void *(*gcry_handler_free_t) (void *)'.
Special memory allocation functions can be installed with the
following function:
-- Function: void gcry_set_allocation_handler (gcry_handler_alloc_t
FUNC_ALLOC, gcry_handler_alloc_t FUNC_ALLOC_SECURE,
gcry_handler_secure_check_t FUNC_SECURE_CHECK,
gcry_handler_realloc_t FUNC_REALLOC, gcry_handler_free_t
FUNC_FREE)
Install the provided functions and use them instead of the built-in
functions for doing memory allocation. Using this function is in
general not recommended because the standard Libgcrypt allocation
functions are guaranteed to zeroize memory if needed.
This function may be used only during initialization and may not be
used in fips mode.

File: gcrypt.info, Node: Error handler, Next: Logging handler, Prev: Allocation handler, Up: Handler Functions
4.3 Error handler
=================
The following functions may be used to register handler functions that
are called by Libgcrypt in case certain error conditions occur. They
may and should be registered prior to calling `gcry_check_version'.
-- Data type: gcry_handler_no_mem_t
This type is defined as: `int (*gcry_handler_no_mem_t) (void *,
size_t, unsigned int)'
-- Function: void gcry_set_outofcore_handler (gcry_handler_no_mem_t
FUNC_NO_MEM, void *CB_DATA)
This function registers FUNC_NO_MEM as `out-of-core handler',
which means that it will be called in the case of not having enough
memory available. The handler is called with 3 arguments: The
first one is the pointer CB_DATA as set with this function, the
second is the requested memory size and the last being a flag. If
bit 0 of the flag is set, secure memory has been requested. The
handler should either return true to indicate that Libgcrypt
should try again allocating memory or return false to let
Libgcrypt use its default fatal error handler.
-- Data type: gcry_handler_error_t
This type is defined as: `void (*gcry_handler_error_t) (void *,
int, const char *)'
-- Function: void gcry_set_fatalerror_handler (gcry_handler_error_t
FUNC_ERROR, void *CB_DATA)
This function registers FUNC_ERROR as `error handler', which means
that it will be called in error conditions.

File: gcrypt.info, Node: Logging handler, Prev: Error handler, Up: Handler Functions
4.4 Logging handler
===================
-- Data type: gcry_handler_log_t
This type is defined as: `void (*gcry_handler_log_t) (void *, int,
const char *, va_list)'
-- Function: void gcry_set_log_handler (gcry_handler_log_t FUNC_LOG,
void *CB_DATA)
This function registers FUNC_LOG as `logging handler', which means
that it will be called in case Libgcrypt wants to log a message.
This function may and should be used prior to calling
`gcry_check_version'.

File: gcrypt.info, Node: Symmetric cryptography, Next: Public Key cryptography, Prev: Handler Functions, Up: Top
5 Symmetric cryptography
************************
The cipher functions are used for symmetrical cryptography, i.e.
cryptography using a shared key. The programming model follows an
open/process/close paradigm and is in that similar to other building
blocks provided by Libgcrypt.
* Menu:
* Available ciphers:: List of ciphers supported by the library.
* Available cipher modes:: List of cipher modes supported by the library.
* Working with cipher handles:: How to perform operations related to cipher handles.
* General cipher functions:: General cipher functions independent of cipher handles.

File: gcrypt.info, Node: Available ciphers, Next: Available cipher modes, Up: Symmetric cryptography
5.1 Available ciphers
=====================
`GCRY_CIPHER_NONE'
This is not a real algorithm but used by some functions as error
return. The value always evaluates to false.
`GCRY_CIPHER_IDEA'
This is the IDEA algorithm.
`GCRY_CIPHER_3DES'
Triple-DES with 3 Keys as EDE. The key size of this algorithm is
168 but you have to pass 192 bits because the most significant
bits of each byte are ignored.
`GCRY_CIPHER_CAST5'
CAST128-5 block cipher algorithm. The key size is 128 bits.
`GCRY_CIPHER_BLOWFISH'
The blowfish algorithm. The current implementation allows only for
a key size of 128 bits.
`GCRY_CIPHER_SAFER_SK128'
Reserved and not currently implemented.
`GCRY_CIPHER_DES_SK'
Reserved and not currently implemented.
`GCRY_CIPHER_AES'
`GCRY_CIPHER_AES128'
`GCRY_CIPHER_RIJNDAEL'
`GCRY_CIPHER_RIJNDAEL128'
AES (Rijndael) with a 128 bit key.
`GCRY_CIPHER_AES192'
`GCRY_CIPHER_RIJNDAEL192'
AES (Rijndael) with a 192 bit key.
`GCRY_CIPHER_AES256'
`GCRY_CIPHER_RIJNDAEL256'
AES (Rijndael) with a 256 bit key.
`GCRY_CIPHER_TWOFISH'
The Twofish algorithm with a 256 bit key.
`GCRY_CIPHER_TWOFISH128'
The Twofish algorithm with a 128 bit key.
`GCRY_CIPHER_ARCFOUR'
An algorithm which is 100% compatible with RSA Inc.'s RC4
algorithm. Note that this is a stream cipher and must be used
very carefully to avoid a couple of weaknesses.
`GCRY_CIPHER_DES'
Standard DES with a 56 bit key. You need to pass 64 bit but the
high bits of each byte are ignored. Note, that this is a weak
algorithm which can be broken in reasonable time using a brute
force approach.
`GCRY_CIPHER_SERPENT128'
`GCRY_CIPHER_SERPENT192'
`GCRY_CIPHER_SERPENT256'
The Serpent cipher from the AES contest.
`GCRY_CIPHER_RFC2268_40'
`GCRY_CIPHER_RFC2268_128'
Ron's Cipher 2 in the 40 and 128 bit variants.
`GCRY_CIPHER_SEED'
A 128 bit cipher as described by RFC4269.
`GCRY_CIPHER_CAMELLIA128'
`GCRY_CIPHER_CAMELLIA192'
`GCRY_CIPHER_CAMELLIA256'
The Camellia cipher by NTT. See
`http://info.isl.ntt.co.jp/crypt/eng/camellia/specifications.html'.
`GCRY_CIPHER_SALSA20'
This is the Salsa20 stream cipher.
`GCRY_CIPHER_SALSA20R12'
This is the Salsa20/12 - reduced round version of Salsa20 stream
cipher.
`GCRY_CIPHER_GOST28147'
The GOST 28147-89 cipher, defined in the respective GOST standard.
Translation of this GOST into English is provided in the RFC-5830.

File: gcrypt.info, Node: Available cipher modes, Next: Working with cipher handles, Prev: Available ciphers, Up: Symmetric cryptography
5.2 Available cipher modes
==========================
`GCRY_CIPHER_MODE_NONE'
No mode specified. This should not be used. The only exception
is that if Libgcrypt is not used in FIPS mode and if any debug
flag has been set, this mode may be used to bypass the actual
encryption.
`GCRY_CIPHER_MODE_ECB'
Electronic Codebook mode.
`GCRY_CIPHER_MODE_CFB'
Cipher Feedback mode. The shift size equals the block size of the
cipher (e.g. for AES it is CFB-128).
`GCRY_CIPHER_MODE_CBC'
Cipher Block Chaining mode.
`GCRY_CIPHER_MODE_STREAM'
Stream mode, only to be used with stream cipher algorithms.
`GCRY_CIPHER_MODE_OFB'
Output Feedback mode.
`GCRY_CIPHER_MODE_CTR'
Counter mode.
`GCRY_CIPHER_MODE_AESWRAP'
This mode is used to implement the AES-Wrap algorithm according to
RFC-3394. It may be used with any 128 bit block length algorithm,
however the specs require one of the 3 AES algorithms. These
special conditions apply: If `gcry_cipher_setiv' has not been used
the standard IV is used; if it has been used the lower 64 bit of
the IV are used as the Alternative Initial Value. On encryption
the provided output buffer must be 64 bit (8 byte) larger than the
input buffer; in-place encryption is still allowed. On decryption
the output buffer may be specified 64 bit (8 byte) shorter than
then input buffer. As per specs the input length must be at least
128 bits and the length must be a multiple of 64 bits.
`GCRY_CIPHER_MODE_CCM'
Counter with CBC-MAC mode is an Authenticated Encryption with
Associated Data (AEAD) block cipher mode, which is specified in
'NIST Special Publication 800-38C' and RFC 3610.
`GCRY_CIPHER_MODE_GCM'
Galois/Counter Mode (GCM) is an Authenticated Encryption with
Associated Data (AEAD) block cipher mode, which is specified in
'NIST Special Publication 800-38D'.

File: gcrypt.info, Node: Working with cipher handles, Next: General cipher functions, Prev: Available cipher modes, Up: Symmetric cryptography
5.3 Working with cipher handles
===============================
To use a cipher algorithm, you must first allocate an according handle.
This is to be done using the open function:
-- Function: gcry_error_t gcry_cipher_open (gcry_cipher_hd_t *HD, int
ALGO, int MODE, unsigned int FLAGS)
This function creates the context handle required for most of the
other cipher functions and returns a handle to it in `hd'. In
case of an error, an according error code is returned.
The ID of algorithm to use must be specified via ALGO. See *Note
Available ciphers::, for a list of supported ciphers and the
according constants.
Besides using the constants directly, the function
`gcry_cipher_map_name' may be used to convert the textual name of
an algorithm into the according numeric ID.
The cipher mode to use must be specified via MODE. See *Note
Available cipher modes::, for a list of supported cipher modes and
the according constants. Note that some modes are incompatible
with some algorithms - in particular, stream mode
(`GCRY_CIPHER_MODE_STREAM') only works with stream ciphers. The
block cipher modes (`GCRY_CIPHER_MODE_ECB',
`GCRY_CIPHER_MODE_CBC', `GCRY_CIPHER_MODE_CFB',
`GCRY_CIPHER_MODE_OFB' and `GCRY_CIPHER_MODE_CTR') will work with
any block cipher algorithm. `GCRY_CIPHER_MODE_CCM' and
`GCRY_CIPHER_MODE_GCM' modes will only work with block cipher
algorithms which have the block size of 16 bytes.
The third argument FLAGS can either be passed as `0' or as the
bit-wise OR of the following constants.
`GCRY_CIPHER_SECURE'
Make sure that all operations are allocated in secure memory.
This is useful when the key material is highly confidential.
`GCRY_CIPHER_ENABLE_SYNC'
This flag enables the CFB sync mode, which is a special
feature of Libgcrypt's CFB mode implementation to allow for
OpenPGP's CFB variant. See `gcry_cipher_sync'.
`GCRY_CIPHER_CBC_CTS'
Enable cipher text stealing (CTS) for the CBC mode. Cannot
be used simultaneous as GCRY_CIPHER_CBC_MAC. CTS mode makes
it possible to transform data of almost arbitrary size (only
limitation is that it must be greater than the algorithm's
block size).
`GCRY_CIPHER_CBC_MAC'
Compute CBC-MAC keyed checksums. This is the same as CBC
mode, but only output the last block. Cannot be used
simultaneous as GCRY_CIPHER_CBC_CTS.
Use the following function to release an existing handle:
-- Function: void gcry_cipher_close (gcry_cipher_hd_t H)
This function releases the context created by `gcry_cipher_open'.
It also zeroises all sensitive information associated with this
cipher handle.
In order to use a handle for performing cryptographic operations, a
`key' has to be set first:
-- Function: gcry_error_t gcry_cipher_setkey (gcry_cipher_hd_t H,
const void *K, size_t L)
Set the key K used for encryption or decryption in the context
denoted by the handle H. The length L (in bytes) of the key K
must match the required length of the algorithm set for this
context or be in the allowed range for algorithms with variable
key size. The function checks this and returns an error if there
is a problem. A caller should always check for an error.
Most crypto modes requires an initialization vector (IV), which
usually is a non-secret random string acting as a kind of salt value.
The CTR mode requires a counter, which is also similar to a salt value.
To set the IV or CTR, use these functions:
-- Function: gcry_error_t gcry_cipher_setiv (gcry_cipher_hd_t H, const
void *K, size_t L)
Set the initialization vector used for encryption or decryption.
The vector is passed as the buffer K of length L bytes and copied
to internal data structures. The function checks that the IV
matches the requirement of the selected algorithm and mode.
This function is also used with the Salsa20 stream cipher to set or
update the required nonce. In this case it needs to be called
after setting the key.
This function is also used with the AEAD cipher modes to set or
update the required nonce.
-- Function: gcry_error_t gcry_cipher_setctr (gcry_cipher_hd_t H,
const void *C, size_t L)
Set the counter vector used for encryption or decryption. The
counter is passed as the buffer C of length L bytes and copied to
internal data structures. The function checks that the counter
matches the requirement of the selected algorithm (i.e., it must be
the same size as the block size).
-- Function: gcry_error_t gcry_cipher_reset (gcry_cipher_hd_t H)
Set the given handle's context back to the state it had after the
last call to gcry_cipher_setkey and clear the initialization
vector.
Note that gcry_cipher_reset is implemented as a macro.
Authenticated Encryption with Associated Data (AEAD) block cipher
modes require the handling of the authentication tag and the additional
authenticated data, which can be done by using the following functions:
-- Function: gcry_error_t gcry_cipher_authenticate (gcry_cipher_hd_t
H, const void *ABUF, size_t ABUFLEN)
Process the buffer ABUF of length ABUFLEN as the additional
authenticated data (AAD) for AEAD cipher modes.
-- Function: gcry_error_t gcry_cipher_gettag (gcry_cipher_hd_t H, void
*TAG, size_t TAGLEN)
This function is used to read the authentication tag after
encryption. The function finalizes and outputs the authentication
tag to the buffer TAG of length TAGLEN bytes.
-- Function: gcry_error_t gcry_cipher_checktag (gcry_cipher_hd_t H,
const void *TAG, size_t TAGLEN)
Check the authentication tag after decryption. The authentication
tag is passed as the buffer TAG of length TAGLEN bytes and
compared to internal authentication tag computed during
decryption. Error code `GPG_ERR_CHECKSUM' is returned if the
authentication tag in the buffer TAG does not match the
authentication tag calculated during decryption.
The actual encryption and decryption is done by using one of the
following functions. They may be used as often as required to process
all the data.
-- Function: gcry_error_t gcry_cipher_encrypt (gcry_cipher_hd_t H,
unsigned char *out, size_t OUTSIZE, const unsigned char *IN,
size_t INLEN)
`gcry_cipher_encrypt' is used to encrypt the data. This function
can either work in place or with two buffers. It uses the cipher
context already setup and described by the handle H. There are 2
ways to use the function: If IN is passed as `NULL' and INLEN is
`0', in-place encryption of the data in OUT or length OUTSIZE
takes place. With IN being not `NULL', INLEN bytes are encrypted
to the buffer OUT which must have at least a size of INLEN.
OUTSIZE must be set to the allocated size of OUT, so that the
function can check that there is sufficient space. Note that
overlapping buffers are not allowed.
Depending on the selected algorithms and encryption mode, the
length of the buffers must be a multiple of the block size.
The function returns `0' on success or an error code.
-- Function: gcry_error_t gcry_cipher_decrypt (gcry_cipher_hd_t H,
unsigned char *out, size_t OUTSIZE, const unsigned char *IN,
size_t INLEN)
`gcry_cipher_decrypt' is used to decrypt the data. This function
can either work in place or with two buffers. It uses the cipher
context already setup and described by the handle H. There are 2
ways to use the function: If IN is passed as `NULL' and INLEN is
`0', in-place decryption of the data in OUT or length OUTSIZE
takes place. With IN being not `NULL', INLEN bytes are decrypted
to the buffer OUT which must have at least a size of INLEN.
OUTSIZE must be set to the allocated size of OUT, so that the
function can check that there is sufficient space. Note that
overlapping buffers are not allowed.
Depending on the selected algorithms and encryption mode, the
length of the buffers must be a multiple of the block size.
The function returns `0' on success or an error code.
OpenPGP (as defined in RFC-2440) requires a special sync operation in
some places. The following function is used for this:
-- Function: gcry_error_t gcry_cipher_sync (gcry_cipher_hd_t H)
Perform the OpenPGP sync operation on context H. Note that this
is a no-op unless the context was created with the flag
`GCRY_CIPHER_ENABLE_SYNC'
Some of the described functions are implemented as macros utilizing a
catch-all control function. This control function is rarely used
directly but there is nothing which would inhibit it:
-- Function: gcry_error_t gcry_cipher_ctl (gcry_cipher_hd_t H, int
CMD, void *BUFFER, size_t BUFLEN)
`gcry_cipher_ctl' controls various aspects of the cipher module and
specific cipher contexts. Usually some more specialized functions
or macros are used for this purpose. The semantics of the
function and its parameters depends on the the command CMD and the
passed context handle H. Please see the comments in the source
code (`src/global.c') for details.
-- Function: gcry_error_t gcry_cipher_info (gcry_cipher_hd_t H, int
WHAT, void *BUFFER, size_t *NBYTES)
`gcry_cipher_info' is used to retrieve various information about a
cipher context or the cipher module in general.
Currently no information is available.

File: gcrypt.info, Node: General cipher functions, Prev: Working with cipher handles, Up: Symmetric cryptography
5.4 General cipher functions
============================
To work with the algorithms, several functions are available to map
algorithm names to the internal identifiers, as well as ways to
retrieve information about an algorithm or the current cipher context.
-- Function: gcry_error_t gcry_cipher_algo_info (int ALGO, int WHAT,
void *BUFFER, size_t *NBYTES)
This function is used to retrieve information on a specific
algorithm. You pass the cipher algorithm ID as ALGO and the type
of information requested as WHAT. The result is either returned as
the return code of the function or copied to the provided BUFFER
whose allocated length must be available in an integer variable
with the address passed in NBYTES. This variable will also
receive the actual used length of the buffer.
Here is a list of supported codes for WHAT:
`GCRYCTL_GET_KEYLEN:'
Return the length of the key. If the algorithm supports
multiple key lengths, the maximum supported value is
returned. The length is returned as number of octets (bytes)
and not as number of bits in NBYTES; BUFFER must be zero.
Note that it is usually better to use the convenience function
`gcry_cipher_get_algo_keylen'.
`GCRYCTL_GET_BLKLEN:'
Return the block length of the algorithm. The length is
returned as a number of octets in NBYTES; BUFFER must be
zero. Note that it is usually better to use the convenience
function `gcry_cipher_get_algo_blklen'.
`GCRYCTL_TEST_ALGO:'
Returns `0' when the specified algorithm is available for use.
BUFFER and NBYTES must be zero.
-- Function: size_t gcry_cipher_get_algo_keylen (ALGO)
This function returns length of the key for algorithm ALGO. If
the algorithm supports multiple key lengths, the maximum supported
key length is returned. On error `0' is returned. The key length
is returned as number of octets.
This is a convenience functions which should be preferred over
`gcry_cipher_algo_info' because it allows for proper type checking.
-- Function: size_t gcry_cipher_get_algo_blklen (int ALGO)
This functions returns the block-length of the algorithm ALGO
counted in octets. On error `0' is returned.
This is a convenience functions which should be preferred over
`gcry_cipher_algo_info' because it allows for proper type checking.
-- Function: const char * gcry_cipher_algo_name (int ALGO)
`gcry_cipher_algo_name' returns a string with the name of the
cipher algorithm ALGO. If the algorithm is not known or another
error occurred, the string `"?"' is returned. This function should
not be used to test for the availability of an algorithm.
-- Function: int gcry_cipher_map_name (const char *NAME)
`gcry_cipher_map_name' returns the algorithm identifier for the
cipher algorithm described by the string NAME. If this algorithm
is not available `0' is returned.
-- Function: int gcry_cipher_mode_from_oid (const char *STRING)
Return the cipher mode associated with an ASN.1 object identifier.
The object identifier is expected to be in the IETF-style dotted
decimal notation. The function returns `0' for an unknown object
identifier or when no mode is associated with it.

File: gcrypt.info, Node: Public Key cryptography, Next: Hashing, Prev: Symmetric cryptography, Up: Top
6 Public Key cryptography
*************************
Public key cryptography, also known as asymmetric cryptography, is an
easy way for key management and to provide digital signatures.
Libgcrypt provides two completely different interfaces to public key
cryptography, this chapter explains the one based on S-expressions.
* Menu:
* Available algorithms:: Algorithms supported by the library.
* Used S-expressions:: Introduction into the used S-expression.
* Cryptographic Functions:: Functions for performing the cryptographic actions.
* General public-key related Functions:: General functions, not implementing any cryptography.

File: gcrypt.info, Node: Available algorithms, Next: Used S-expressions, Up: Public Key cryptography
6.1 Available algorithms
========================
Libgcrypt supports the RSA (Rivest-Shamir-Adleman) algorithms as well
as DSA (Digital Signature Algorithm) and Elgamal. The versatile
interface allows to add more algorithms in the future.

File: gcrypt.info, Node: Used S-expressions, Next: Cryptographic Functions, Prev: Available algorithms, Up: Public Key cryptography
6.2 Used S-expressions
======================
Libgcrypt's API for asymmetric cryptography is based on data structures
called S-expressions (see
`http://people.csail.mit.edu/rivest/sexp.html') and does not work with
contexts as most of the other building blocks of Libgcrypt do.
The following information are stored in S-expressions:
* keys
* plain text data
* encrypted data
* signatures
To describe how Libgcrypt expect keys, we use examples. Note that words
in uppercase indicate parameters whereas lowercase words are literals.
Note that all MPI (multi-precision-integers) values are expected to
be in `GCRYMPI_FMT_USG' format. An easy way to create S-expressions is
by using `gcry_sexp_build' which allows to pass a string with
printf-like escapes to insert MPI values.
* Menu:
* RSA key parameters:: Parameters used with an RSA key.
* DSA key parameters:: Parameters used with a DSA key.
* ECC key parameters:: Parameters used with ECC keys.

File: gcrypt.info, Node: RSA key parameters, Next: DSA key parameters, Up: Used S-expressions
6.2.1 RSA key parameters
------------------------
An RSA private key is described by this S-expression:
(private-key
(rsa
(n N-MPI)
(e E-MPI)
(d D-MPI)
(p P-MPI)
(q Q-MPI)
(u U-MPI)))
An RSA public key is described by this S-expression:
(public-key
(rsa
(n N-MPI)
(e E-MPI)))
N-MPI
RSA public modulus n.
E-MPI
RSA public exponent e.
D-MPI
RSA secret exponent d = e^-1 \bmod (p-1)(q-1).
P-MPI
RSA secret prime p.
Q-MPI
RSA secret prime q with p < q.
U-MPI
Multiplicative inverse u = p^-1 \bmod q.
For signing and decryption the parameters (p, q, u) are optional but
greatly improve the performance. Either all of these optional
parameters must be given or none of them. They are mandatory for
gcry_pk_testkey.
Note that OpenSSL uses slighly different parameters: q < p and u =
q^-1 \bmod p. To use these parameters you will need to swap the values
and recompute u. Here is example code to do this:
if (gcry_mpi_cmp (p, q) > 0)
{
gcry_mpi_swap (p, q);
gcry_mpi_invm (u, p, q);
}

File: gcrypt.info, Node: DSA key parameters, Next: ECC key parameters, Prev: RSA key parameters, Up: Used S-expressions
6.2.2 DSA key parameters
------------------------
A DSA private key is described by this S-expression:
(private-key
(dsa
(p P-MPI)
(q Q-MPI)
(g G-MPI)
(y Y-MPI)
(x X-MPI)))
P-MPI
DSA prime p.
Q-MPI
DSA group order q (which is a prime divisor of p-1).
G-MPI
DSA group generator g.
Y-MPI
DSA public key value y = g^x \bmod p.
X-MPI
DSA secret exponent x.
The public key is similar with "private-key" replaced by "public-key"
and no X-MPI.

File: gcrypt.info, Node: ECC key parameters, Prev: DSA key parameters, Up: Used S-expressions
6.2.3 ECC key parameters
------------------------
An ECC private key is described by this S-expression:
(private-key
(ecc
(p P-MPI)
(a A-MPI)
(b B-MPI)
(g G-POINT)
(n N-MPI)
(q Q-POINT)
(d D-MPI)))
P-MPI
Prime specifying the field GF(p).
A-MPI
B-MPI
The two coefficients of the Weierstrass equation y^2 = x^3 + ax + b
G-POINT
Base point g.
N-MPI
Order of g
Q-POINT
The point representing the public key Q = dG.
D-MPI
The private key d
All point values are encoded in standard format; Libgcrypt does in
general only support uncompressed points, thus the first byte needs to
be `0x04'. However "EdDSA" describes its own compression scheme which
is used by default.
The public key is similar with "private-key" replaced by "public-key"
and no D-MPI.
If the domain parameters are well-known, the name of this curve may
be used. For example
(private-key
(ecc
(curve "NIST P-192")
(q Q-POINT)
(d D-MPI)))
Note that Q-POINT is optional for a private key. The `curve'
parameter may be given in any case and is used to replace missing
parameters.
Currently implemented curves are:
`NIST P-192'
`1.2.840.10045.3.1.1'
`prime192v1'
`secp192r1'
The NIST 192 bit curve, its OID, X9.62 and SECP aliases.
`NIST P-224'
`secp224r1'
The NIST 224 bit curve and its SECP alias.
`NIST P-256'
`1.2.840.10045.3.1.7'
`prime256v1'
`secp256r1'
The NIST 256 bit curve, its OID, X9.62 and SECP aliases.
`NIST P-384'
`secp384r1'
The NIST 384 bit curve and its SECP alias.
`NIST P-521'
`secp521r1'
The NIST 521 bit curve and its SECP alias.
As usual the OIDs may optionally be prefixed with the string `OID.'
or `oid.'.

File: gcrypt.info, Node: Cryptographic Functions, Next: General public-key related Functions, Prev: Used S-expressions, Up: Public Key cryptography
6.3 Cryptographic Functions
===========================
Some functions operating on S-expressions support `flags' to influence
the operation. These flags have to be listed in a sub-S-expression
named `flags'. Flag names are case-sensitive. The following flags are
known:
`comp'
`nocomp'
If supported by the algorithm and curve the `comp' flag requests
that points are returned in compact (compressed) representation.
The `nocomp' flag requests that points are returned with full
coordinates. The default depends on the the algorithm and curve.
The compact representation requires a small overhead before a point
can be used but halves the size of a to be conveyed public key.
`pkcs1'
Use PKCS#1 block type 2 padding for encryption, block type 1
padding for signing.
`oaep'
Use RSA-OAEP padding for encryption.
`pss'
Use RSA-PSS padding for signing.
`eddsa'
Use the EdDSA scheme signing instead of the default ECDSA
algorithm. Note that the EdDSA uses a special form of the public
key.
`rfc6979'
For DSA and ECDSA use a deterministic scheme for the k parameter.
`no-blinding'
Do not use a technique called `blinding', which is used by default
in order to prevent leaking of secret information. Blinding is
only implemented by RSA, but it might be implemented by other
algorithms in the future as well, when necessary.
`param'
For ECC key generation also return the domain parameters. For ECC
signing and verification override default parameters by provided
domain parameters of the public or private key.
`transient-key'
This flag is only meaningful for RSA, DSA, and ECC key generation.
If given the key is created using a faster and a somewhat less
secure random number generator. This flag may be used for keys
which are only used for a short time or per-message and do not
require full cryptographic strength.
`use-x931'
Force the use of the ANSI X9.31 key generation algorithm instead of
the default algorithm. This flag is only meaningful for RSA key
generation and usually not required. Note that this algorithm is
implicitly used if either `derive-parms' is given or Libgcrypt is
in FIPS mode.
`use-fips186'
Force the use of the FIPS 186 key generation algorithm instead of
the default algorithm. This flag is only meaningful for DSA and
usually not required. Note that this algorithm is implicitly used
if either `derive-parms' is given or Libgcrypt is in FIPS mode.
As of now FIPS 186-2 is implemented; after the approval of FIPS
186-3 the code will be changed to implement 186-3.
`use-fips186-2'
Force the use of the FIPS 186-2 key generation algorithm instead of
the default algorithm. This algorithm is slightly different from
FIPS 186-3 and allows only 1024 bit keys. This flag is only
meaningful for DSA and only required for FIPS testing backward
compatibility.
Now that we know the key basics, we can carry on and explain how to
encrypt and decrypt data. In almost all cases the data is a random
session key which is in turn used for the actual encryption of the real
data. There are 2 functions to do this:
-- Function: gcry_error_t gcry_pk_encrypt (gcry_sexp_t *R_CIPH,
gcry_sexp_t DATA, gcry_sexp_t PKEY)
Obviously a public key must be provided for encryption. It is
expected as an appropriate S-expression (see above) in PKEY. The
data to be encrypted can either be in the simple old format, which
is a very simple S-expression consisting only of one MPI, or it
may be a more complex S-expression which also allows to specify
flags for operation, like e.g. padding rules.
If you don't want to let Libgcrypt handle the padding, you must
pass an appropriate MPI using this expression for DATA:
(data
(flags raw)
(value MPI))
This has the same semantics as the old style MPI only way. MPI is
the actual data, already padded appropriate for your protocol.
Most RSA based systems however use PKCS#1 padding and so you can
use this S-expression for DATA:
(data
(flags pkcs1)
(value BLOCK))
Here, the "flags" list has the "pkcs1" flag which let the function
know that it should provide PKCS#1 block type 2 padding. The
actual data to be encrypted is passed as a string of octets in
BLOCK. The function checks that this data actually can be used
with the given key, does the padding and encrypts it.
If the function could successfully perform the encryption, the
return value will be 0 and a new S-expression with the encrypted
result is allocated and assigned to the variable at the address of
R_CIPH. The caller is responsible to release this value using
`gcry_sexp_release'. In case of an error, an error code is
returned and R_CIPH will be set to `NULL'.
The returned S-expression has this format when used with RSA:
(enc-val
(rsa
(a A-MPI)))
Where A-MPI is an MPI with the result of the RSA operation. When
using the Elgamal algorithm, the return value will have this
format:
(enc-val
(elg
(a A-MPI)
(b B-MPI)))
Where A-MPI and B-MPI are MPIs with the result of the Elgamal
encryption operation.
-- Function: gcry_error_t gcry_pk_decrypt (gcry_sexp_t *R_PLAIN,
gcry_sexp_t DATA, gcry_sexp_t SKEY)
Obviously a private key must be provided for decryption. It is
expected as an appropriate S-expression (see above) in SKEY. The
data to be decrypted must match the format of the result as
returned by `gcry_pk_encrypt', but should be enlarged with a
`flags' element:
(enc-val
(flags)
(elg
(a A-MPI)
(b B-MPI)))
This function does not remove padding from the data by default. To
let Libgcrypt remove padding, give a hint in `flags' telling which
padding method was used when encrypting:
(flags PADDING-METHOD)
Currently PADDING-METHOD is either `pkcs1' for PKCS#1 block type 2
padding, or `oaep' for RSA-OAEP padding.
The function returns 0 on success or an error code. The variable
at the address of R_PLAIN will be set to NULL on error or receive
the decrypted value on success. The format of R_PLAIN is a simple
S-expression part (i.e. not a valid one) with just one MPI if
there was no `flags' element in DATA; if at least an empty `flags'
is passed in DATA, the format is:
(value PLAINTEXT)
Another operation commonly performed using public key cryptography is
signing data. In some sense this is even more important than
encryption because digital signatures are an important instrument for
key management. Libgcrypt supports digital signatures using 2
functions, similar to the encryption functions:
-- Function: gcry_error_t gcry_pk_sign (gcry_sexp_t *R_SIG,
gcry_sexp_t DATA, gcry_sexp_t SKEY)
This function creates a digital signature for DATA using the
private key SKEY and place it into the variable at the address of
R_SIG. DATA may either be the simple old style S-expression with
just one MPI or a modern and more versatile S-expression which
allows to let Libgcrypt handle padding:
(data
(flags pkcs1)
(hash HASH-ALGO BLOCK))
This example requests to sign the data in BLOCK after applying
PKCS#1 block type 1 style padding. HASH-ALGO is a string with the
hash algorithm to be encoded into the signature, this may be any
hash algorithm name as supported by Libgcrypt. Most likely, this
will be "sha256" or "sha1". It is obvious that the length of
BLOCK must match the size of that message digests; the function
checks that this and other constraints are valid.
If PKCS#1 padding is not required (because the caller does already
provide a padded value), either the old format or better the
following format should be used:
(data
(flags raw)
(value MPI))
Here, the data to be signed is directly given as an MPI.
For DSA the input data is expected in this format:
(data
(flags raw)
(value MPI))
Here, the data to be signed is directly given as an MPI. It is
expect that this MPI is the the hash value. For the standard DSA
using a MPI is not a problem in regard to leading zeroes because
the hash value is directly used as an MPI. For better standard
conformance it would be better to explicit use a memory string
(like with pkcs1) but that is currently not supported. However,
for deterministic DSA as specified in RFC6979 this can't be used.
Instead the following input is expected.
(data
(flags rfc6979)
(hash HASH-ALGO BLOCK))
Note that the provided hash-algo is used for the internal HMAC; it
should match the hash-algo used to create BLOCK.
The signature is returned as a newly allocated S-expression in
R_SIG using this format for RSA:
(sig-val
(rsa
(s S-MPI)))
Where S-MPI is the result of the RSA sign operation. For DSA the
S-expression returned is:
(sig-val
(dsa
(r R-MPI)
(s S-MPI)))
Where R-MPI and S-MPI are the result of the DSA sign operation.
For Elgamal signing (which is slow, yields large numbers and
probably is not as secure as the other algorithms), the same
format is used with "elg" replacing "dsa"; for ECDSA signing, the
same format is used with "ecdsa" replacing "dsa".
For the EdDSA algorithm (cf. Ed25515) the required input
parameters are:
(data
(flags eddsa)
(hash-algo sha512)
(value MESSAGE))
Note that the MESSAGE may be of any length; hashing is part of the
algorithm. Using a large data block for MESSAGE is not suggested;
in that case the used protocol should better require that a hash
of the message is used as input to the EdDSA algorithm.
The operation most commonly used is definitely the verification of a
signature. Libgcrypt provides this function:
-- Function: gcry_error_t gcry_pk_verify (gcry_sexp_t SIG,
gcry_sexp_t DATA, gcry_sexp_t PKEY)
This is used to check whether the signature SIG matches the DATA.
The public key PKEY must be provided to perform this verification.
This function is similar in its parameters to `gcry_pk_sign' with
the exceptions that the public key is used instead of the private
key and that no signature is created but a signature, in a format
as created by `gcry_pk_sign', is passed to the function in SIG.
The result is 0 for success (i.e. the data matches the signature),
or an error code where the most relevant code is
`GCRY_ERR_BAD_SIGNATURE' to indicate that the signature does not
match the provided data.

File: gcrypt.info, Node: General public-key related Functions, Prev: Cryptographic Functions, Up: Public Key cryptography
6.4 General public-key related Functions
========================================
A couple of utility functions are available to retrieve the length of
the key, map algorithm identifiers and perform sanity checks:
-- Function: const char * gcry_pk_algo_name (int ALGO)
Map the public key algorithm id ALGO to a string representation of
the algorithm name. For unknown algorithms this functions returns
the string `"?"'. This function should not be used to test for the
availability of an algorithm.
-- Function: int gcry_pk_map_name (const char *NAME)
Map the algorithm NAME to a public key algorithm Id. Returns 0 if
the algorithm name is not known.
-- Function: int gcry_pk_test_algo (int ALGO)
Return 0 if the public key algorithm ALGO is available for use.
Note that this is implemented as a macro.
-- Function: unsigned int gcry_pk_get_nbits (gcry_sexp_t KEY)
Return what is commonly referred as the key length for the given
public or private in KEY.
-- Function: unsigned char * gcry_pk_get_keygrip (gcry_sexp_t KEY,
unsigned char *ARRAY)
Return the so called "keygrip" which is the SHA-1 hash of the
public key parameters expressed in a way depended on the
algorithm. ARRAY must either provide space for 20 bytes or be
`NULL'. In the latter case a newly allocated array of that size is
returned. On success a pointer to the newly allocated space or to
ARRAY is returned. `NULL' is returned to indicate an error which
is most likely an unknown algorithm or one where a "keygrip" has
not yet been defined. The function accepts public or secret keys
in KEY.
-- Function: gcry_error_t gcry_pk_testkey (gcry_sexp_t KEY)
Return zero if the private key KEY is `sane', an error code
otherwise. Note that it is not possible to check the `saneness'
of a public key.
-- Function: gcry_error_t gcry_pk_algo_info (int ALGO, int WHAT,
void *BUFFER, size_t *NBYTES)
Depending on the value of WHAT return various information about
the public key algorithm with the id ALGO. Note that the function
returns `-1' on error and the actual error code must be retrieved
using the function `gcry_errno'. The currently defined values for
WHAT are:
`GCRYCTL_TEST_ALGO:'
Return 0 if the specified algorithm is available for use.
BUFFER must be `NULL', NBYTES may be passed as `NULL' or
point to a variable with the required usage of the algorithm.
This may be 0 for "don't care" or the bit-wise OR of these
flags:
`GCRY_PK_USAGE_SIGN'
Algorithm is usable for signing.
`GCRY_PK_USAGE_ENCR'
Algorithm is usable for encryption.
Unless you need to test for the allowed usage, it is in
general better to use the macro gcry_pk_test_algo instead.
`GCRYCTL_GET_ALGO_USAGE:'
Return the usage flags for the given algorithm. An invalid
algorithm return 0. Disabled algorithms are ignored here
because we want to know whether the algorithm is at all
capable of a certain usage.
`GCRYCTL_GET_ALGO_NPKEY'
Return the number of elements the public key for algorithm
ALGO consist of. Return 0 for an unknown algorithm.
`GCRYCTL_GET_ALGO_NSKEY'
Return the number of elements the private key for algorithm
ALGO consist of. Note that this value is always larger than
that of the public key. Return 0 for an unknown algorithm.
`GCRYCTL_GET_ALGO_NSIGN'
Return the number of elements a signature created with the
algorithm ALGO consists of. Return 0 for an unknown
algorithm or for an algorithm not capable of creating
signatures.
`GCRYCTL_GET_ALGO_NENC'
Return the number of elements a encrypted message created
with the algorithm ALGO consists of. Return 0 for an unknown
algorithm or for an algorithm not capable of encryption.
Please note that parameters not required should be passed as
`NULL'.
-- Function: gcry_error_t gcry_pk_ctl (int CMD, void *BUFFER,
size_t BUFLEN)
This is a general purpose function to perform certain control
operations. CMD controls what is to be done. The return value is
0 for success or an error code. Currently supported values for
CMD are:
`GCRYCTL_DISABLE_ALGO'
Disable the algorithm given as an algorithm id in BUFFER.
BUFFER must point to an `int' variable with the algorithm id
and BUFLEN must have the value `sizeof (int)'. This fucntion
is not thread safe and should thus be used before any other
threads are started.
Libgcrypt also provides a function to generate public key pairs:
-- Function: gcry_error_t gcry_pk_genkey (gcry_sexp_t *R_KEY,
gcry_sexp_t PARMS)
This function create a new public key pair using information given
in the S-expression PARMS and stores the private and the public key
in one new S-expression at the address given by R_KEY. In case of
an error, R_KEY is set to `NULL'. The return code is 0 for
success or an error code otherwise.
Here is an example for PARMS to create an 2048 bit RSA key:
(genkey
(rsa
(nbits 4:2048)))
To create an Elgamal key, substitute "elg" for "rsa" and to create
a DSA key use "dsa". Valid ranges for the key length depend on the
algorithms; all commonly used key lengths are supported. Currently
supported parameters are:
`nbits'
This is always required to specify the length of the key. The
argument is a string with a number in C-notation. The value
should be a multiple of 8. Note that the S-expression syntax
requires that a number is prefixed with its string length;
thus the `4:' in the above example.
`curve NAME'
For ECC a named curve may be used instead of giving the
number of requested bits. This allows to request a specific
curve to override a default selection Libgcrypt would have
taken if `nbits' has been given. The available names are
listed with the description of the ECC public key parameters.
`rsa-use-e VALUE'
This is only used with RSA to give a hint for the public
exponent. The VALUE will be used as a base to test for a
usable exponent. Some values are special:
`0'
Use a secure and fast value. This is currently the
number 41.
`1'
Use a value as required by some crypto policies. This
is currently the number 65537.
`2'
Reserved
`> 2'
Use the given value.
If this parameter is not used, Libgcrypt uses for historic
reasons 65537.
`qbits N'
This is only meanigful for DSA keys. If it is given the DSA
key is generated with a Q parameyer of size N bits. If it is
not given or zero Q is deduced from NBITS in this way:
`512 <= N <= 1024'
Q = 160
`N = 2048'
Q = 224
`N = 3072'
Q = 256
`N = 7680'
Q = 384
`N = 15360'
Q = 512
Note that in this case only the values for N, as given in the
table, are allowed. When specifying Q all values of N in the
range 512 to 15680 are valid as long as they are multiples of
8.
`domain LIST'
This is only meaningful for DLP algorithms. If specified
keys are generated with domain parameters taken from this
list. The exact format of this parameter depends on the
actual algorithm. It is currently only implemented for DSA
using this format:
(genkey
(dsa
(domain
(p P-MPI)
(q Q-MPI)
(g Q-MPI))))
`nbits' and `qbits' may not be specified because they are
derived from the domain parameters.
`derive-parms LIST'
This is currently only implemented for RSA and DSA keys. It
is not allowed to use this together with a `domain'
specification. If given, it is used to derive the keys using
the given parameters.
If given for an RSA key the X9.31 key generation algorithm is
used even if libgcrypt is not in FIPS mode. If given for a
DSA key, the FIPS 186 algorithm is used even if libgcrypt is
not in FIPS mode.
(genkey
(rsa
(nbits 4:1024)
(rsa-use-e 1:3)
(derive-parms
(Xp1 #1A1916DDB29B4EB7EB6732E128#)
(Xp2 #192E8AAC41C576C822D93EA433#)
(Xp #D8CD81F035EC57EFE822955149D3BFF70C53520D
769D6D76646C7A792E16EBD89FE6FC5B605A6493
39DFC925A86A4C6D150B71B9EEA02D68885F5009
B98BD984#)
(Xq1 #1A5CF72EE770DE50CB09ACCEA9#)
(Xq2 #134E4CAA16D2350A21D775C404#)
(Xq #CC1092495D867E64065DEE3E7955F2EBC7D47A2D
7C9953388F97DDDC3E1CA19C35CA659EDC2FC325
6D29C2627479C086A699A49C4C9CEE7EF7BD1B34
321DE34A#))))
(genkey
(dsa
(nbits 4:1024)
(derive-parms
(seed SEED-MPI))))
`flags FLAGLIST'
This is preferred way to define flags. FLAGLIST may contain
any number of flags. See above for a specification of these
flags.
Here is an example on how to create a key using curve Ed25519
with the ECDSA signature algorithm. Note that the use of
ECDSA with that curve is in general not recommended.
(genkey
(ecc
(flags transient-key)))
`transient-key'
`use-x931'
`use-fips186'
`use-fips186-2'
These are deprecated ways to set a flag with that name; see
above for a description of each flag.
The key pair is returned in a format depending on the algorithm.
Both private and public keys are returned in one container and may
be accompanied by some miscellaneous information.
Here are two examples; the first for Elgamal and the second for
elliptic curve key generation:
(key-data
(public-key
(elg
(p P-MPI)
(g G-MPI)
(y Y-MPI)))
(private-key
(elg
(p P-MPI)
(g G-MPI)
(y Y-MPI)
(x X-MPI)))
(misc-key-info
(pm1-factors N1 N2 ... NN))
(key-data
(public-key
(ecc
(curve Ed25519)
(flags eddsa)
(q Q-VALUE)))
(private-key
(ecc
(curve Ed25519)
(flags eddsa)
(q Q-VALUE)
(d D-VALUE))))
As you can see, some of the information is duplicated, but this
provides an easy way to extract either the public or the private
key. Note that the order of the elements is not defined, e.g. the
private key may be stored before the public key. N1 N2 ... NN is a
list of prime numbers used to composite P-MPI; this is in general
not a very useful information and only available if the key
generation algorithm provides them.
Future versions of Libgcrypt will have extended versions of the public
key interfaced which will take an additional context to allow for
pre-computations, special operations, and other optimization. As a
first step a new function is introduced to help using the ECC
algorithms in new ways:
-- Function: gcry_error_t gcry_pubkey_get_sexp (gcry_sexp_t *R_SEXP,
int MODE, gcry_ctx_t CTX)
Return an S-expression representing the context CTX. Depending on
the state of that context, the S-expression may either be a public
key, a private key or any other object used with public key
operations. On success 0 is returned and a new S-expression is
stored at R_SEXP; on error an error code is returned and NULL is
stored at R_SEXP. MODE must be one of:
`0'
Decide what to return depending on the context. For example
if the private key parameter is available a private key is
returned, if not a public key is returned.
`GCRY_PK_GET_PUBKEY'
Return the public key even if the context has the private key
parameter.
`GCRY_PK_GET_SECKEY'
Return the private key or the error `GPG_ERR_NO_SECKEY' if it
is not possible.
As of now this function supports only certain ECC operations
because a context object is right now only defined for ECC. Over
time this function will be extended to cover more algorithms.

File: gcrypt.info, Node: Hashing, Next: Message Authentication Codes, Prev: Public Key cryptography, Up: Top
7 Hashing
*********
Libgcrypt provides an easy and consistent to use interface for hashing.
Hashing is buffered and several hash algorithms can be updated at once.
It is possible to compute a HMAC using the same routines. The
programming model follows an open/process/close paradigm and is in that
similar to other building blocks provided by Libgcrypt.
For convenience reasons, a few cyclic redundancy check value
operations are also supported.
* Menu:
* Available hash algorithms:: List of hash algorithms supported by the library.
* Working with hash algorithms:: List of functions related to hashing.

File: gcrypt.info, Node: Available hash algorithms, Next: Working with hash algorithms, Up: Hashing
7.1 Available hash algorithms
=============================
`GCRY_MD_NONE'
This is not a real algorithm but used by some functions as an error
return value. This constant is guaranteed to have the value `0'.
`GCRY_MD_SHA1'
This is the SHA-1 algorithm which yields a message digest of 20
bytes. Note that SHA-1 begins to show some weaknesses and it is
suggested to fade out its use if strong cryptographic properties
are required.
`GCRY_MD_RMD160'
This is the 160 bit version of the RIPE message digest
(RIPE-MD-160). Like SHA-1 it also yields a digest of 20 bytes.
This algorithm share a lot of design properties with SHA-1 and
thus it is advisable not to use it for new protocols.
`GCRY_MD_MD5'
This is the well known MD5 algorithm, which yields a message
digest of 16 bytes. Note that the MD5 algorithm has severe
weaknesses, for example it is easy to compute two messages
yielding the same hash (collision attack). The use of this
algorithm is only justified for non-cryptographic application.
`GCRY_MD_MD4'
This is the MD4 algorithm, which yields a message digest of 16
bytes. This algorithm has severe weaknesses and should not be
used.
`GCRY_MD_MD2'
This is an reserved identifier for MD-2; there is no
implementation yet. This algorithm has severe weaknesses and
should not be used.
`GCRY_MD_TIGER'
This is the TIGER/192 algorithm which yields a message digest of 24
bytes. Actually this is a variant of TIGER with a different output
print order as used by GnuPG up to version 1.3.2.
`GCRY_MD_TIGER1'
This is the TIGER variant as used by the NESSIE project. It uses
the most commonly used output print order.
`GCRY_MD_TIGER2'
This is another variant of TIGER with a different padding scheme.
`GCRY_MD_HAVAL'
This is an reserved value for the HAVAL algorithm with 5 passes
and 160 bit. It yields a message digest of 20 bytes. Note that
there is no implementation yet available.
`GCRY_MD_SHA224'
This is the SHA-224 algorithm which yields a message digest of 28
bytes. See Change Notice 1 for FIPS 180-2 for the specification.
`GCRY_MD_SHA256'
This is the SHA-256 algorithm which yields a message digest of 32
bytes. See FIPS 180-2 for the specification.
`GCRY_MD_SHA384'
This is the SHA-384 algorithm which yields a message digest of 48
bytes. See FIPS 180-2 for the specification.
`GCRY_MD_SHA512'
This is the SHA-384 algorithm which yields a message digest of 64
bytes. See FIPS 180-2 for the specification.
`GCRY_MD_CRC32'
This is the ISO 3309 and ITU-T V.42 cyclic redundancy check. It
yields an output of 4 bytes. Note that this is not a hash
algorithm in the cryptographic sense.
`GCRY_MD_CRC32_RFC1510'
This is the above cyclic redundancy check function, as modified by
RFC 1510. It yields an output of 4 bytes. Note that this is not
a hash algorithm in the cryptographic sense.
`GCRY_MD_CRC24_RFC2440'
This is the OpenPGP cyclic redundancy check function. It yields an
output of 3 bytes. Note that this is not a hash algorithm in the
cryptographic sense.
`GCRY_MD_WHIRLPOOL'
This is the Whirlpool algorithm which yields a message digest of 64
bytes.
`GCRY_MD_GOSTR3411_94'
This is the hash algorithm described in GOST R 34.11-94 which
yields a message digest of 32 bytes.
`GCRY_MD_STRIBOG256'
This is the 256-bit version of hash algorithm described in GOST R
34.11-2012 which yields a message digest of 32 bytes.
`GCRY_MD_STRIBOG512'
This is the 512-bit version of hash algorithm described in GOST R
34.11-2012 which yields a message digest of 64 bytes.

File: gcrypt.info, Node: Working with hash algorithms, Prev: Available hash algorithms, Up: Hashing
7.2 Working with hash algorithms
================================
To use most of these function it is necessary to create a context; this
is done using:
-- Function: gcry_error_t gcry_md_open (gcry_md_hd_t *HD, int ALGO,
unsigned int FLAGS)
Create a message digest object for algorithm ALGO. FLAGS may be
given as an bitwise OR of constants described below. ALGO may be
given as `0' if the algorithms to use are later set using
`gcry_md_enable'. HD is guaranteed to either receive a valid
handle or NULL.
For a list of supported algorithms, see *Note Available hash
algorithms::.
The flags allowed for MODE are:
`GCRY_MD_FLAG_SECURE'
Allocate all buffers and the resulting digest in "secure
memory". Use this is the hashed data is highly confidential.
`GCRY_MD_FLAG_HMAC'
Turn the algorithm into a HMAC message authentication
algorithm. This only works if just one algorithm is enabled
for the handle. Note that the function `gcry_md_setkey' must
be used to set the MAC key. The size of the MAC is equal to
the message digest of the underlying hash algorithm. If you
want CBC message authentication codes based on a cipher, see
*Note Working with cipher handles::.
`GCRY_MD_FLAG_BUGEMU1'
Versions of Libgcrypt before 1.6.0 had a bug in the Whirlpool
code which led to a wrong result for certain input sizes and
write patterns. Using this flag emulates that bug. This may
for example be useful for applications which use Whirlpool as
part of their key generation. It is strongly suggested to
use this flag only if really needed and if possible to the
data should be re-processed using the regular Whirlpool
algorithm.
Note that this flag works for the entire hash context. If
needed arises it may be used to enable bug emulation for
other hash algorithms. Thus you should not use this flag for
a multi-algorithm hash context.
You may use the function `gcry_md_is_enabled' to later check
whether an algorithm has been enabled.
If you want to calculate several hash algorithms at the same time,
you have to use the following function right after the `gcry_md_open':
-- Function: gcry_error_t gcry_md_enable (gcry_md_hd_t H, int ALGO)
Add the message digest algorithm ALGO to the digest object
described by handle H. Duplicated enabling of algorithms is
detected and ignored.
If the flag `GCRY_MD_FLAG_HMAC' was used, the key for the MAC must
be set using the function:
-- Function: gcry_error_t gcry_md_setkey (gcry_md_hd_t H, const void
*KEY, size_t KEYLEN)
For use with the HMAC feature, set the MAC key to the value of KEY
of length KEYLEN bytes. There is no restriction on the length of
the key.
After you are done with the hash calculation, you should release the
resources by using:
-- Function: void gcry_md_close (gcry_md_hd_t H)
Release all resources of hash context H. H should not be used
after a call to this function. A `NULL' passed as H is ignored.
The function also zeroises all sensitive information associated
with this handle.
Often you have to do several hash operations using the same
algorithm. To avoid the overhead of creating and releasing context, a
reset function is provided:
-- Function: void gcry_md_reset (gcry_md_hd_t H)
Reset the current context to its initial state. This is
effectively identical to a close followed by an open and enabling
all currently active algorithms.
Often it is necessary to start hashing some data and then continue to
hash different data. To avoid hashing the same data several times
(which might not even be possible if the data is received from a pipe),
a snapshot of the current hash context can be taken and turned into a
new context:
-- Function: gcry_error_t gcry_md_copy (gcry_md_hd_t *HANDLE_DST,
gcry_md_hd_t HANDLE_SRC)
Create a new digest object as an exact copy of the object
described by handle HANDLE_SRC and store it in HANDLE_DST. The
context is not reset and you can continue to hash data using this
context and independently using the original context.
Now that we have prepared everything to calculate hashes, it is time
to see how it is actually done. There are two ways for this, one to
update the hash with a block of memory and one macro to update the hash
by just one character. Both methods can be used on the same hash
context.
-- Function: void gcry_md_write (gcry_md_hd_t H, const void *BUFFER,
size_t LENGTH)
Pass LENGTH bytes of the data in BUFFER to the digest object with
handle H to update the digest values. This function should be used
for large blocks of data.
-- Function: void gcry_md_putc (gcry_md_hd_t H, int C)
Pass the byte in C to the digest object with handle H to update
the digest value. This is an efficient function, implemented as a
macro to buffer the data before an actual update.
The semantics of the hash functions do not provide for reading out
intermediate message digests because the calculation must be finalized
first. This finalization may for example include the number of bytes
hashed in the message digest or some padding.
-- Function: void gcry_md_final (gcry_md_hd_t H)
Finalize the message digest calculation. This is not really needed
because `gcry_md_read' does this implicitly. After this has been
done no further updates (by means of `gcry_md_write' or
`gcry_md_putc' are allowed. Only the first call to this function
has an effect. It is implemented as a macro.
The way to read out the calculated message digest is by using the
function:
-- Function: unsigned char * gcry_md_read (gcry_md_hd_t H, int ALGO)
`gcry_md_read' returns the message digest after finalizing the
calculation. This function may be used as often as required but
it will always return the same value for one handle. The returned
message digest is allocated within the message context and
therefore valid until the handle is released or reseted (using
`gcry_md_close' or `gcry_md_reset'. ALGO may be given as 0 to
return the only enabled message digest or it may specify one of
the enabled algorithms. The function does return `NULL' if the
requested algorithm has not been enabled.
Because it is often necessary to get the message digest of blocks of
memory, two fast convenience function are available for this task:
-- Function: gpg_err_code_t gcry_md_hash_buffers ( int ALGO,
unsigned int FLAGS, void *DIGEST, const gcry_buffer_t *IOV,
int IOVCNT )
`gcry_md_hash_buffers' is a shortcut function to calculate a
message digest from several buffers. This function does not
require a context and immediately returns the message digest of of
the data described by IOV and IOVCNT. DIGEST must be allocated by
the caller, large enough to hold the message digest yielded by the
the specified algorithm ALGO. This required size may be obtained
by using the function `gcry_md_get_algo_dlen'.
IOV is an array of buffer descriptions with IOVCNT items. The
caller should zero out the structures in this array and for each
array item set the fields `.data' to the address of the data to be
hashed, `.len' to number of bytes to be hashed. If .OFF is also
set, the data is taken starting at .OFF bytes from the begin of
the buffer. The field `.size' is not used.
The only supported flag value for FLAGS is GCRY_MD_FLAG_HMAC which
turns this function into a HMAC function; the first item in IOV is
then used as the key.
On success the function returns 0 and stores the resulting hash or
MAC at DIGEST.
-- Function: void gcry_md_hash_buffer (int ALGO, void *DIGEST, const
void *BUFFER, size_t LENGTH);
`gcry_md_hash_buffer' is a shortcut function to calculate a message
digest of a buffer. This function does not require a context and
immediately returns the message digest of the LENGTH bytes at
BUFFER. DIGEST must be allocated by the caller, large enough to
hold the message digest yielded by the the specified algorithm
ALGO. This required size may be obtained by using the function
`gcry_md_get_algo_dlen'.
Note that in contrast to `gcry_md_hash_buffers' this function will
abort the process if an unavailable algorithm is used.
Hash algorithms are identified by internal algorithm numbers (see
`gcry_md_open' for a list). However, in most applications they are
used by names, so two functions are available to map between string
representations and hash algorithm identifiers.
-- Function: const char * gcry_md_algo_name (int ALGO)
Map the digest algorithm id ALGO to a string representation of the
algorithm name. For unknown algorithms this function returns the
string `"?"'. This function should not be used to test for the
availability of an algorithm.
-- Function: int gcry_md_map_name (const char *NAME)
Map the algorithm with NAME to a digest algorithm identifier.
Returns 0 if the algorithm name is not known. Names representing
ASN.1 object identifiers are recognized if the IETF dotted format
is used and the OID is prefixed with either "`oid.'" or "`OID.'".
For a list of supported OIDs, see the source code at
`cipher/md.c'. This function should not be used to test for the
availability of an algorithm.
-- Function: gcry_error_t gcry_md_get_asnoid (int ALGO, void *BUFFER,
size_t *LENGTH)
Return an DER encoded ASN.1 OID for the algorithm ALGO in the user
allocated BUFFER. LENGTH must point to variable with the available
size of BUFFER and receives after return the actual size of the
returned OID. The returned error code may be `GPG_ERR_TOO_SHORT'
if the provided buffer is to short to receive the OID; it is
possible to call the function with `NULL' for BUFFER to have it
only return the required size. The function returns 0 on success.
To test whether an algorithm is actually available for use, the
following macro should be used:
-- Function: gcry_error_t gcry_md_test_algo (int ALGO)
The macro returns 0 if the algorithm ALGO is available for use.
If the length of a message digest is not known, it can be retrieved
using the following function:
-- Function: unsigned int gcry_md_get_algo_dlen (int ALGO)
Retrieve the length in bytes of the digest yielded by algorithm
ALGO. This is often used prior to `gcry_md_read' to allocate
sufficient memory for the digest.
In some situations it might be hard to remember the algorithm used
for the ongoing hashing. The following function might be used to get
that information:
-- Function: int gcry_md_get_algo (gcry_md_hd_t H)
Retrieve the algorithm used with the handle H. Note that this
does not work reliable if more than one algorithm is enabled in H.
The following macro might also be useful:
-- Function: int gcry_md_is_secure (gcry_md_hd_t H)
This function returns true when the digest object H is allocated
in "secure memory"; i.e. H was created with the
`GCRY_MD_FLAG_SECURE'.
-- Function: int gcry_md_is_enabled (gcry_md_hd_t H, int ALGO)
This function returns true when the algorithm ALGO has been
enabled for the digest object H.
Tracking bugs related to hashing is often a cumbersome task which
requires to add a lot of printf statements into the code. Libgcrypt
provides an easy way to avoid this. The actual data hashed can be
written to files on request.
-- Function: void gcry_md_debug (gcry_md_hd_t H, const char *SUFFIX)
Enable debugging for the digest object with handle H. This
creates create files named `dbgmd-<n>.<string>' while doing the
actual hashing. SUFFIX is the string part in the filename. The
number is a counter incremented for each new hashing. The data in
the file is the raw data as passed to `gcry_md_write' or
`gcry_md_putc'. If `NULL' is used for SUFFIX, the debugging is
stopped and the file closed. This is only rarely required because
`gcry_md_close' implicitly stops debugging.

File: gcrypt.info, Node: Message Authentication Codes, Next: Key Derivation, Prev: Hashing, Up: Top
8 Message Authentication Codes
******************************
Libgcrypt provides an easy and consistent to use interface for
generating Message Authentication Codes (MAC). MAC generation is
buffered and interface similar to the one used with hash algorithms.
The programming model follows an open/process/close paradigm and is in
that similar to other building blocks provided by Libgcrypt.
* Menu:
* Available MAC algorithms:: List of MAC algorithms supported by the library.
* Working with MAC algorithms:: List of functions related to MAC algorithms.

File: gcrypt.info, Node: Available MAC algorithms, Next: Working with MAC algorithms, Up: Message Authentication Codes
8.1 Available MAC algorithms
============================
`GCRY_MAC_NONE'
This is not a real algorithm but used by some functions as an error
return value. This constant is guaranteed to have the value `0'.
`GCRY_MAC_HMAC_SHA256'
This is keyed-hash message authentication code (HMAC) message
authentication algorithm based on the SHA-256 hash algorithm.
`GCRY_MAC_HMAC_SHA224'
This is HMAC message authentication algorithm based on the SHA-224
hash algorithm.
`GCRY_MAC_HMAC_SHA512'
This is HMAC message authentication algorithm based on the SHA-512
hash algorithm.
`GCRY_MAC_HMAC_SHA384'
This is HMAC message authentication algorithm based on the SHA-384
hash algorithm.
`GCRY_MAC_HMAC_SHA1'
This is HMAC message authentication algorithm based on the SHA-1
hash algorithm.
`GCRY_MAC_HMAC_MD5'
This is HMAC message authentication algorithm based on the MD5 hash
algorithm.
`GCRY_MAC_HMAC_MD4'
This is HMAC message authentication algorithm based on the MD4 hash
algorithm.
`GCRY_MAC_HMAC_RMD160'
This is HMAC message authentication algorithm based on the
RIPE-MD-160 hash algorithm.
`GCRY_MAC_HMAC_WHIRLPOOL'
This is HMAC message authentication algorithm based on the
WHIRLPOOL hash algorithm.
`GCRY_MAC_HMAC_GOSTR3411_94'
This is HMAC message authentication algorithm based on the GOST R
34.11-94 hash algorithm.
`GCRY_MAC_HMAC_STRIBOG256'
This is HMAC message authentication algorithm based on the 256-bit
hash algorithm described in GOST R 34.11-2012.
`GCRY_MAC_HMAC_STRIBOG512'
This is HMAC message authentication algorithm based on the 512-bit
hash algorithm described in GOST R 34.11-2012.
`GCRY_MAC_CMAC_AES'
This is CMAC (Cipher-based MAC) message authentication algorithm
based on the AES block cipher algorithm.
`GCRY_MAC_CMAC_3DES'
This is CMAC message authentication algorithm based on the
three-key EDE Triple-DES block cipher algorithm.
`GCRY_MAC_CMAC_CAMELLIA'
This is CMAC message authentication algorithm based on the
Camellia block cipher algorithm.
`GCRY_MAC_CMAC_CAST5'
This is CMAC message authentication algorithm based on the
CAST128-5 block cipher algorithm.
`GCRY_MAC_CMAC_BLOWFISH'
This is CMAC message authentication algorithm based on the Blowfish
block cipher algorithm.
`GCRY_MAC_CMAC_TWOFISH'
This is CMAC message authentication algorithm based on the Twofish
block cipher algorithm.
`GCRY_MAC_CMAC_SERPENT'
This is CMAC message authentication algorithm based on the Serpent
block cipher algorithm.
`GCRY_MAC_CMAC_SEED'
This is CMAC message authentication algorithm based on the SEED
block cipher algorithm.
`GCRY_MAC_CMAC_RFC2268'
This is CMAC message authentication algorithm based on the Ron's
Cipher 2 block cipher algorithm.
`GCRY_MAC_CMAC_IDEA'
This is CMAC message authentication algorithm based on the IDEA
block cipher algorithm.
`GCRY_MAC_CMAC_GOST28147'
This is CMAC message authentication algorithm based on the GOST
28147-89 block cipher algorithm.
`GCRY_MAC_GMAC_AES'
This is GMAC (GCM mode based MAC) message authentication algorithm
based on the AES block cipher algorithm.
`GCRY_MAC_GMAC_CAMELLIA'
This is GMAC message authentication algorithm based on the Camellia
block cipher algorithm.
`GCRY_MAC_GMAC_TWOFISH'
This is GMAC message authentication algorithm based on the Twofish
block cipher algorithm.
`GCRY_MAC_GMAC_SERPENT'
This is GMAC message authentication algorithm based on the Serpent
block cipher algorithm.
`GCRY_MAC_GMAC_SEED'
This is GMAC message authentication algorithm based on the SEED
block cipher algorithm.

File: gcrypt.info, Node: Working with MAC algorithms, Prev: Available MAC algorithms, Up: Message Authentication Codes
8.2 Working with MAC algorithms
===============================
To use most of these function it is necessary to create a context; this
is done using:
-- Function: gcry_error_t gcry_mac_open (gcry_mac_hd_t *HD, int ALGO,
unsigned int FLAGS, gcry_ctx_t CTX)
Create a MAC object for algorithm ALGO. FLAGS may be given as an
bitwise OR of constants described below. HD is guaranteed to either
receive a valid handle or NULL. CTX is context object to associate
MAC object with. CTX maybe set to NULL.
For a list of supported algorithms, see *Note Available MAC
algorithms::.
The flags allowed for MODE are:
`GCRY_MAC_FLAG_SECURE'
Allocate all buffers and the resulting MAC in "secure
memory". Use this if the MAC data is highly confidential.
In order to use a handle for performing MAC algorithm operations, a
`key' has to be set first:
-- Function: gcry_error_t gcry_mac_setkey (gcry_mac_hd_t H, const void
*KEY, size_t KEYLEN)
Set the MAC key to the value of KEY of length KEYLEN bytes. With
HMAC algorithms, there is no restriction on the length of the key.
With CMAC algorithms, the length of the key is restricted to those
supported by the underlying block cipher.
GMAC algorithms need initialization vector to be set, which can be
performed with function:
-- Function: gcry_error_t gcry_mac_setiv (gcry_mac_hd_t H, const void
*IV, size_t IVLEN)
Set the IV to the value of IV of length IVLEN bytes.
After you are done with the MAC calculation, you should release the
resources by using:
-- Function: void gcry_mac_close (gcry_mac_hd_t H)
Release all resources of MAC context H. H should not be used
after a call to this function. A `NULL' passed as H is ignored.
The function also clears all sensitive information associated with
this handle.
Often you have to do several MAC operations using the same algorithm.
To avoid the overhead of creating and releasing context, a reset
function is provided:
-- Function: gcry_error_t gcry_mac_reset (gcry_mac_hd_t H)
Reset the current context to its initial state. This is
effectively identical to a close followed by an open and setting
same key.
Note that gcry_mac_reset is implemented as a macro.
Now that we have prepared everything to calculate MAC, it is time to
see how it is actually done.
-- Function: gcry_error_t gcry_mac_write (gcry_mac_hd_t H, const void
*BUFFER, size_t LENGTH)
Pass LENGTH bytes of the data in BUFFER to the MAC object with
handle H to update the MAC values.
The way to read out the calculated MAC is by using the function:
-- Function: gcry_error_t gcry_mac_read (gcry_mac_hd_t H, void
*BUFFER, size_t *LENGTH)
`gcry_mac_read' returns the MAC after finalizing the calculation.
Function copies the resulting MAC value to BUFFER of the length
LENGTH. If LENGTH is larger than length of resulting MAC value,
then length of MAC is returned through LENGTH.
To compare existing MAC value with recalculated MAC, one is to use
the function:
-- Function: gcry_error_t gcry_mac_verify (gcry_mac_hd_t H, void
*BUFFER, size_t LENGTH)
`gcry_mac_verify' finalizes MAC calculation and compares result
with LENGTH bytes of data in BUFFER. Error code `GPG_ERR_CHECKSUM'
is returned if the MAC value in the buffer BUFFER does not match
the MAC calculated in object H.
MAC algorithms are identified by internal algorithm numbers (see
`gcry_mac_open' for a list). However, in most applications they are
used by names, so two functions are available to map between string
representations and MAC algorithm identifiers.
-- Function: const char * gcry_mac_algo_name (int ALGO)
Map the MAC algorithm id ALGO to a string representation of the
algorithm name. For unknown algorithms this function returns the
string `"?"'. This function should not be used to test for the
availability of an algorithm.
-- Function: int gcry_mac_map_name (const char *NAME)
Map the algorithm with NAME to a MAC algorithm identifier.
Returns 0 if the algorithm name is not known. This function should
not be used to test for the availability of an algorithm.
To test whether an algorithm is actually available for use, the
following macro should be used:
-- Function: gcry_error_t gcry_mac_test_algo (int ALGO)
The macro returns 0 if the MAC algorithm ALGO is available for use.
If the length of a message digest is not known, it can be retrieved
using the following function:
-- Function: unsigned int gcry_mac_get_algo_maclen (int ALGO)
Retrieve the length in bytes of the MAC yielded by algorithm ALGO.
This is often used prior to `gcry_mac_read' to allocate sufficient
memory for the MAC value. On error `0' is returned.
-- Function: unsigned int gcry_mac_get_algo_keylen (ALGO)
This function returns length of the key for MAC algorithm ALGO. If
the algorithm supports multiple key lengths, the default supported
key length is returned. On error `0' is returned. The key length
is returned as number of octets.

File: gcrypt.info, Node: Key Derivation, Next: Random Numbers, Prev: Message Authentication Codes, Up: Top
9 Key Derivation
****************
Libgcypt provides a general purpose function to derive keys from
strings.
-- Function: gpg_error_t gcry_kdf_derive ( const void *PASSPHRASE,
size_t PASSPHRASELEN, int ALGO, int SUBALGO,
const void *SALT, size_t SALTLEN, unsigned long ITERATIONS,
size_t KEYSIZE, void *KEYBUFFER )
Derive a key from a passphrase. KEYSIZE gives the requested size
of the keys in octets. KEYBUFFER is a caller provided buffer
filled on success with the derived key. The input passphrase is
taken from PASSPHRASE which is an arbitrary memory buffer of
PASSPHRASELEN octets. ALGO specifies the KDF algorithm to use;
see below. SUBALGO specifies an algorithm used internally by the
KDF algorithms; this is usually a hash algorithm but certain KDF
algorithms may use it differently. SALT is a salt of length
SALTLEN octets, as needed by most KDF algorithms. ITERATIONS is a
positive integer parameter to most KDFs.
On success 0 is returned; on failure an error code.
Currently supported KDFs (parameter ALGO):
`GCRY_KDF_SIMPLE_S2K'
The OpenPGP simple S2K algorithm (cf. RFC4880). Its use is
strongly deprecated. SALT and ITERATIONS are not needed and
may be passed as `NULL'/`0'.
`GCRY_KDF_SALTED_S2K'
The OpenPGP salted S2K algorithm (cf. RFC4880). Usually not
used. ITERATIONS is not needed and may be passed as `0'.
SALTLEN must be given as 8.
`GCRY_KDF_ITERSALTED_S2K'
The OpenPGP iterated+salted S2K algorithm (cf. RFC4880).
This is the default for most OpenPGP applications. SALTLEN
must be given as 8. Note that OpenPGP defines a special
encoding of the ITERATIONS; however this function takes the
plain decoded iteration count.
`GCRY_KDF_PBKDF2'
The PKCS#5 Passphrase Based Key Derivation Function number 2.
`GCRY_KDF_SCRYPT'
The SCRYPT Key Derivation Function. The subalgorithm is used
to specify the CPU/memory cost parameter N, and the number of
iterations is used for the parallelization parameter p. The
block size is fixed at 8 in the current implementation.

File: gcrypt.info, Node: Random Numbers, Next: S-expressions, Prev: Key Derivation, Up: Top
10 Random Numbers
*****************
* Menu:
* Quality of random numbers:: Libgcrypt uses different quality levels.
* Retrieving random numbers:: How to retrieve random numbers.

File: gcrypt.info, Node: Quality of random numbers, Next: Retrieving random numbers, Up: Random Numbers
10.1 Quality of random numbers
==============================
Libgcypt offers random numbers of different quality levels:
-- Data type: gcry_random_level_t
The constants for the random quality levels are of this enum type.
`GCRY_WEAK_RANDOM'
For all functions, except for `gcry_mpi_randomize', this level maps
to GCRY_STRONG_RANDOM. If you do not want this, consider using
`gcry_create_nonce'.
`GCRY_STRONG_RANDOM'
Use this level for session keys and similar purposes.
`GCRY_VERY_STRONG_RANDOM'
Use this level for long term key material.

File: gcrypt.info, Node: Retrieving random numbers, Prev: Quality of random numbers, Up: Random Numbers
10.2 Retrieving random numbers
==============================
-- Function: void gcry_randomize (unsigned char *BUFFER, size_t
LENGTH, enum gcry_random_level LEVEL)
Fill BUFFER with LENGTH random bytes using a random quality as
defined by LEVEL.
-- Function: void * gcry_random_bytes (size_t NBYTES, enum
gcry_random_level LEVEL)
Convenience function to allocate a memory block consisting of
NBYTES fresh random bytes using a random quality as defined by
LEVEL.
-- Function: void * gcry_random_bytes_secure (size_t NBYTES, enum
gcry_random_level LEVEL)
Convenience function to allocate a memory block consisting of
NBYTES fresh random bytes using a random quality as defined by
LEVEL. This function differs from `gcry_random_bytes' in that the
returned buffer is allocated in a "secure" area of the memory.
-- Function: void gcry_create_nonce (unsigned char *BUFFER, size_t
LENGTH)
Fill BUFFER with LENGTH unpredictable bytes. This is commonly
called a nonce and may also be used for initialization vectors and
padding. This is an extra function nearly independent of the
other random function for 3 reasons: It better protects the
regular random generator's internal state, provides better
performance and does not drain the precious entropy pool.

File: gcrypt.info, Node: S-expressions, Next: MPI library, Prev: Random Numbers, Up: Top
11 S-expressions
****************
S-expressions are used by the public key functions to pass complex data
structures around. These LISP like objects are used by some
cryptographic protocols (cf. RFC-2692) and Libgcrypt provides functions
to parse and construct them. For detailed information, see `Ron
Rivest, code and description of S-expressions,
`http://theory.lcs.mit.edu/~rivest/sexp.html''.
* Menu:
* Data types for S-expressions:: Data types related with S-expressions.
* Working with S-expressions:: How to work with S-expressions.

File: gcrypt.info, Node: Data types for S-expressions, Next: Working with S-expressions, Up: S-expressions
11.1 Data types for S-expressions
=================================
-- Data type: gcry_sexp_t
The `gcry_sexp_t' type describes an object with the Libgcrypt
internal representation of an S-expression.

File: gcrypt.info, Node: Working with S-expressions, Prev: Data types for S-expressions, Up: S-expressions
11.2 Working with S-expressions
===============================
There are several functions to create an Libgcrypt S-expression object
from its external representation or from a string template. There is
also a function to convert the internal representation back into one of
the external formats:
-- Function: gcry_error_t gcry_sexp_new (gcry_sexp_t *R_SEXP,
const void *BUFFER, size_t LENGTH, int AUTODETECT)
This is the generic function to create an new S-expression object
from its external representation in BUFFER of LENGTH bytes. On
success the result is stored at the address given by R_SEXP. With
AUTODETECT set to 0, the data in BUFFER is expected to be in
canonized format, with AUTODETECT set to 1 the parses any of the
defined external formats. If BUFFER does not hold a valid
S-expression an error code is returned and R_SEXP set to `NULL'.
Note that the caller is responsible for releasing the newly
allocated S-expression using `gcry_sexp_release'.
-- Function: gcry_error_t gcry_sexp_create (gcry_sexp_t *R_SEXP,
void *BUFFER, size_t LENGTH, int AUTODETECT,
void (*FREEFNC)(void*))
This function is identical to `gcry_sexp_new' but has an extra
argument FREEFNC, which, when not set to `NULL', is expected to be
a function to release the BUFFER; most likely the standard `free'
function is used for this argument. This has the effect of
transferring the ownership of BUFFER to the created object in
R_SEXP. The advantage of using this function is that Libgcrypt
might decide to directly use the provided buffer and thus avoid
extra copying.
-- Function: gcry_error_t gcry_sexp_sscan (gcry_sexp_t *R_SEXP,
size_t *ERROFF, const char *BUFFER, size_t LENGTH)
This is another variant of the above functions. It behaves nearly
identical but provides an ERROFF argument which will receive the
offset into the buffer where the parsing stopped on error.
-- Function: gcry_error_t gcry_sexp_build (gcry_sexp_t *R_SEXP,
size_t *ERROFF, const char *FORMAT, ...)
This function creates an internal S-expression from the string
template FORMAT and stores it at the address of R_SEXP. If there
is a parsing error, the function returns an appropriate error code
and stores the offset into FORMAT where the parsing stopped in
ERROFF. The function supports a couple of printf-like formatting
characters and expects arguments for some of these escape
sequences right after FORMAT. The following format characters are
defined:
`%m'
The next argument is expected to be of type `gcry_mpi_t' and
a copy of its value is inserted into the resulting
S-expression. The MPI is stored as a signed integer.
`%M'
The next argument is expected to be of type `gcry_mpi_t' and
a copy of its value is inserted into the resulting
S-expression. The MPI is stored as an unsigned integer.
`%s'
The next argument is expected to be of type `char *' and that
string is inserted into the resulting S-expression.
`%d'
The next argument is expected to be of type `int' and its
value is inserted into the resulting S-expression.
`%u'
The next argument is expected to be of type `unsigned int' and
its value is inserted into the resulting S-expression.
`%b'
The next argument is expected to be of type `int' directly
followed by an argument of type `char *'. This represents a
buffer of given length to be inserted into the resulting
S-expression.
`%S'
The next argument is expected to be of type `gcry_sexp_t' and
a copy of that S-expression is embedded in the resulting
S-expression. The argument needs to be a regular
S-expression, starting with a parenthesis.
No other format characters are defined and would return an error.
Note that the format character `%%' does not exists, because a
percent sign is not a valid character in an S-expression.
-- Function: void gcry_sexp_release (gcry_sexp_t SEXP)
Release the S-expression object SEXP. If the S-expression is
stored in secure memory it explicitly zeroises that memory; note
that this is done in addition to the zeroisation always done when
freeing secure memory.
The next 2 functions are used to convert the internal representation
back into a regular external S-expression format and to show the
structure for debugging.
-- Function: size_t gcry_sexp_sprint (gcry_sexp_t SEXP, int MODE,
char *BUFFER, size_t MAXLENGTH)
Copies the S-expression object SEXP into BUFFER using the format
specified in MODE. MAXLENGTH must be set to the allocated length
of BUFFER. The function returns the actual length of valid bytes
put into BUFFER or 0 if the provided buffer is too short. Passing
`NULL' for BUFFER returns the required length for BUFFER. For
convenience reasons an extra byte with value 0 is appended to the
buffer.
The following formats are supported:
`GCRYSEXP_FMT_DEFAULT'
Returns a convenient external S-expression representation.
`GCRYSEXP_FMT_CANON'
Return the S-expression in canonical format.
`GCRYSEXP_FMT_BASE64'
Not currently supported.
`GCRYSEXP_FMT_ADVANCED'
Returns the S-expression in advanced format.
-- Function: void gcry_sexp_dump (gcry_sexp_t SEXP)
Dumps SEXP in a format suitable for debugging to Libgcrypt's
logging stream.
Often canonical encoding is used in the external representation. The
following function can be used to check for valid encoding and to learn
the length of the S-expression"
-- Function: size_t gcry_sexp_canon_len (const unsigned char *BUFFER,
size_t LENGTH, size_t *ERROFF, int *ERRCODE)
Scan the canonical encoded BUFFER with implicit length values and
return the actual length this S-expression uses. For a valid
S-expression it should never return 0. If LENGTH is not 0, the
maximum length to scan is given; this can be used for syntax
checks of data passed from outside. ERRCODE and ERROFF may both be
passed as `NULL'.
There are functions to parse S-expressions and retrieve elements:
-- Function: gcry_sexp_t gcry_sexp_find_token (const gcry_sexp_t LIST,
const char *TOKEN, size_t TOKLEN)
Scan the S-expression for a sublist with a type (the car of the
list) matching the string TOKEN. If TOKLEN is not 0, the token is
assumed to be raw memory of this length. The function returns a
newly allocated S-expression consisting of the found sublist or
`NULL' when not found.
-- Function: int gcry_sexp_length (const gcry_sexp_t LIST)
Return the length of the LIST. For a valid S-expression this
should be at least 1.
-- Function: gcry_sexp_t gcry_sexp_nth (const gcry_sexp_t LIST,
int NUMBER)
Create and return a new S-expression from the element with index
NUMBER in LIST. Note that the first element has the index 0. If
there is no such element, `NULL' is returned.
-- Function: gcry_sexp_t gcry_sexp_car (const gcry_sexp_t LIST)
Create and return a new S-expression from the first element in
LIST; this is called the "type" and should always exist per
S-expression specification and in general be a string. `NULL' is
returned in case of a problem.
-- Function: gcry_sexp_t gcry_sexp_cdr (const gcry_sexp_t LIST)
Create and return a new list form all elements except for the
first one. Note that this function may return an invalid
S-expression because it is not guaranteed, that the type exists
and is a string. However, for parsing a complex S-expression it
might be useful for intermediate lists. Returns `NULL' on error.
-- Function: const char * gcry_sexp_nth_data (const gcry_sexp_t LIST,
int NUMBER, size_t *DATALEN)
This function is used to get data from a LIST. A pointer to the
actual data with index NUMBER is returned and the length of this
data will be stored to DATALEN. If there is no data at the given
index or the index represents another list, `NULL' is returned.
*Caution:* The returned pointer is valid as long as LIST is not
modified or released.
Here is an example on how to extract and print the surname (Meier)
from the S-expression `(Name Otto Meier (address Burgplatz 3))':
size_t len;
const char *name;
name = gcry_sexp_nth_data (list, 2, &len);
printf ("my name is %.*s\n", (int)len, name);
-- Function: void * gcry_sexp_nth_buffer (const gcry_sexp_t LIST,
int NUMBER, size_t *RLENGTH)
This function is used to get data from a LIST. A malloced buffer
with the actual data at list index NUMBER is returned and the
length of this buffer will be stored to RLENGTH. If there is no
data at the given index or the index represents another list,
`NULL' is returned. The caller must release the result using
`gcry_free'.
Here is an example on how to extract and print the CRC value from
the S-expression `(hash crc32 #23ed00d7)':
size_t len;
char *value;
value = gcry_sexp_nth_buffer (list, 2, &len);
if (value)
fwrite (value, len, 1, stdout);
gcry_free (value);
-- Function: char * gcry_sexp_nth_string (gcry_sexp_t LIST, int NUMBER)
This function is used to get and convert data from a LIST. The
data is assumed to be a Nul terminated string. The caller must
release this returned value using `gcry_free'. If there is no
data at the given index, the index represents a list or the value
can't be converted to a string, `NULL' is returned.
-- Function: gcry_mpi_t gcry_sexp_nth_mpi (gcry_sexp_t LIST,
int NUMBER, int MPIFMT)
This function is used to get and convert data from a LIST. This
data is assumed to be an MPI stored in the format described by
MPIFMT and returned as a standard Libgcrypt MPI. The caller must
release this returned value using `gcry_mpi_release'. If there is
no data at the given index, the index represents a list or the
value can't be converted to an MPI, `NULL' is returned. If you use
this function to parse results of a public key function, you most
likely want to use `GCRYMPI_FMT_USG'.
-- Function: gpg_error_t gcry_sexp_extract_param ( gcry_sexp_t SEXP,
const char *PATH, const char *LIST, ...)
Extract parameters from an S-expression using a list of parameter
names. The names of these parameters are specified in LIST. White
space between the parameter names are ignored. Some special
characters may be given to control the conversion:
`+'
Switch to unsigned integer format (GCRYMPI_FMT_USG). This is
the default mode.
`-'
Switch to standard signed format (GCRYMPI_FMT_STD).
`/'
Switch to opaque MPI format. The resulting MPIs may not be
used for computations; see `gcry_mpi_get_opaque' for details.
`&'
Switch to buffer descriptor mode. See below for details.
`?'
If immediately following a parameter letter (no white space
allowed), that parameter is considered optional.
In general parameter names are single letters. To use a string
for a parameter name, enclose the name in single quotes.
Unless in buffer descriptor mode for each parameter name a pointer
to an `gcry_mpi_t' variable is expected finally followed by a
`NULL'. For example
_gcry_sexp_extract_param (key, NULL, "n/x+e d-'foo'",
&mpi_n, &mpi_x, &mpi_e, &mpi_foo, NULL)
stores the parameter 'n' from KEY as an unsigned MPI into MPI_N,
the parameter 'x' as an opaque MPI into MPI_X, the parameter 'e'
again as an unsigned MPI into MPI_E, and the parameter 'foo' as a
signed MPI.
PATH is an optional string used to locate a token. The
exclamation mark separated tokens are used via
`gcry_sexp_find_token' to find a start point inside the
S-expression.
In buffer descriptor mode a pointer to a `gcry_buffer_t'
descriptor is expected instead of a pointer to an MPI. The caller
may use two different operation modes here: If the DATA field of
the provided descriptor is `NULL', the function allocates a new
buffer and stores it at DATA; the other fields are set accordingly
with OFF set to 0. If DATA is not `NULL', the function assumes
that the DATA, SIZE, and OFF fields specify a buffer where to but
the value of the respective parameter; on return the LEN field
receives the number of bytes copied to that buffer; in case the
buffer is too small, the function immediately returns with an
error code (and LEN is set to 0).
The function returns NULL on success. On error an error code is
returned and the passed MPIs are either unchanged or set to NULL.

File: gcrypt.info, Node: MPI library, Next: Prime numbers, Prev: S-expressions, Up: Top
12 MPI library
**************
* Menu:
* Data types:: MPI related data types.
* Basic functions:: First steps with MPI numbers.
* MPI formats:: External representation of MPIs.
* Calculations:: Performing MPI calculations.
* Comparisons:: How to compare MPI values.
* Bit manipulations:: How to access single bits of MPI values.
* EC functions:: Elliptic curve related functions.
* Miscellaneous:: Miscellaneous MPI functions.
Public key cryptography is based on mathematics with large numbers.
To implement the public key functions, a library for handling these
large numbers is required. Because of the general usefulness of such a
library, its interface is exposed by Libgcrypt. In the context of
Libgcrypt and in most other applications, these large numbers are
called MPIs (multi-precision-integers).

File: gcrypt.info, Node: Data types, Next: Basic functions, Up: MPI library
12.1 Data types
===============
-- Data type: gcry_mpi_t
This type represents an object to hold an MPI.
-- Data type: gcry_mpi_point_t
This type represents an object to hold a point for elliptic curve
math.

File: gcrypt.info, Node: Basic functions, Next: MPI formats, Prev: Data types, Up: MPI library
12.2 Basic functions
====================
To work with MPIs, storage must be allocated and released for the
numbers. This can be done with one of these functions:
-- Function: gcry_mpi_t gcry_mpi_new (unsigned int NBITS)
Allocate a new MPI object, initialize it to 0 and initially
allocate enough memory for a number of at least NBITS. This
pre-allocation is only a small performance issue and not actually
necessary because Libgcrypt automatically re-allocates the
required memory.
-- Function: gcry_mpi_t gcry_mpi_snew (unsigned int NBITS)
This is identical to `gcry_mpi_new' but allocates the MPI in the so
called "secure memory" which in turn will take care that all
derived values will also be stored in this "secure memory". Use
this for highly confidential data like private key parameters.
-- Function: gcry_mpi_t gcry_mpi_copy (const gcry_mpi_t A)
Create a new MPI as the exact copy of A but with the constant and
immutable flags cleared.
-- Function: void gcry_mpi_release (gcry_mpi_t A)
Release the MPI A and free all associated resources. Passing
`NULL' is allowed and ignored. When a MPI stored in the "secure
memory" is released, that memory gets wiped out immediately.
The simplest operations are used to assign a new value to an MPI:
-- Function: gcry_mpi_t gcry_mpi_set (gcry_mpi_t W, const gcry_mpi_t U)
Assign the value of U to W and return W. If `NULL' is passed for
W, a new MPI is allocated, set to the value of U and returned.
-- Function: gcry_mpi_t gcry_mpi_set_ui (gcry_mpi_t W, unsigned long U)
Assign the value of U to W and return W. If `NULL' is passed for
W, a new MPI is allocated, set to the value of U and returned.
This function takes an `unsigned int' as type for U and thus it is
only possible to set W to small values (usually up to the word
size of the CPU).
-- Function: void gcry_mpi_swap (gcry_mpi_t A, gcry_mpi_t B)
Swap the values of A and B.
-- Function: void gcry_mpi_snatch (gcry_mpi_t W, const gcry_mpi_t U)
Set U into W and release U. If W is `NULL' only U will be
released.
-- Function: void gcry_mpi_neg (gcry_mpi_t W, gcry_mpi_t U)
Set the sign of W to the negative of U.
-- Function: void gcry_mpi_abs (gcry_mpi_t W)
Clear the sign of W.

File: gcrypt.info, Node: MPI formats, Next: Calculations, Prev: Basic functions, Up: MPI library
12.3 MPI formats
================
The following functions are used to convert between an external
representation of an MPI and the internal one of Libgcrypt.
-- Function: gcry_error_t gcry_mpi_scan (gcry_mpi_t *R_MPI,
enum gcry_mpi_format FORMAT, const unsigned char *BUFFER,
size_t BUFLEN, size_t *NSCANNED)
Convert the external representation of an integer stored in BUFFER
with a length of BUFLEN into a newly created MPI returned which
will be stored at the address of R_MPI. For certain formats the
length argument is not required and should be passed as `0'.
After a successful operation the variable NSCANNED receives the
number of bytes actually scanned unless NSCANNED was given as
`NULL'. FORMAT describes the format of the MPI as stored in BUFFER:
`GCRYMPI_FMT_STD'
2-complement stored without a length header. Note that
`gcry_mpi_print' stores a `0' as a string of zero length.
`GCRYMPI_FMT_PGP'
As used by OpenPGP (only defined as unsigned). This is
basically `GCRYMPI_FMT_STD' with a 2 byte big endian length
header.
`GCRYMPI_FMT_SSH'
As used in the Secure Shell protocol. This is
`GCRYMPI_FMT_STD' with a 4 byte big endian header.
`GCRYMPI_FMT_HEX'
Stored as a string with each byte of the MPI encoded as 2 hex
digits. Negative numbers are prefix with a minus sign and in
addition the high bit is always zero to make clear that an
explicit sign ist used. When using this format, BUFLEN must
be zero.
`GCRYMPI_FMT_USG'
Simple unsigned integer.
Note that all of the above formats store the integer in big-endian
format (MSB first).
-- Function: gcry_error_t gcry_mpi_print (enum gcry_mpi_format FORMAT,
unsigned char *BUFFER, size_t BUFLEN, size_t *NWRITTEN,
const gcry_mpi_t A)
Convert the MPI A into an external representation described by
FORMAT (see above) and store it in the provided BUFFER which has a
usable length of at least the BUFLEN bytes. If NWRITTEN is not
NULL, it will receive the number of bytes actually stored in
BUFFER after a successful operation.
-- Function: gcry_error_t gcry_mpi_aprint
(enum gcry_mpi_format FORMAT, unsigned char **BUFFER,
size_t *NBYTES, const gcry_mpi_t A)
Convert the MPI A into an external representation described by
FORMAT (see above) and store it in a newly allocated buffer which
address will be stored in the variable BUFFER points to. The
number of bytes stored in this buffer will be stored in the
variable NBYTES points to, unless NBYTES is `NULL'.
Even if NBYTES is zero, the function allocates at least one byte
and store a zero there. Thus with formats `GCRYMPI_FMT_STD' and
`GCRYMPI_FMT_USG' the caller may safely set a returned length of 0
to 1 to represent a zero as a 1 byte string.
-- Function: void gcry_mpi_dump (const gcry_mpi_t A)
Dump the value of A in a format suitable for debugging to
Libgcrypt's logging stream. Note that one leading space but no
trailing space or linefeed will be printed. It is okay to pass
`NULL' for A.

File: gcrypt.info, Node: Calculations, Next: Comparisons, Prev: MPI formats, Up: MPI library
12.4 Calculations
=================
Basic arithmetic operations:
-- Function: void gcry_mpi_add (gcry_mpi_t W, gcry_mpi_t U,
gcry_mpi_t V)
W = U + V.
-- Function: void gcry_mpi_add_ui (gcry_mpi_t W, gcry_mpi_t U,
unsigned long V)
W = U + V. Note that V is an unsigned integer.
-- Function: void gcry_mpi_addm (gcry_mpi_t W, gcry_mpi_t U,
gcry_mpi_t V, gcry_mpi_t M)
W = U + V \bmod M.
-- Function: void gcry_mpi_sub (gcry_mpi_t W, gcry_mpi_t U,
gcry_mpi_t V)
W = U - V.
-- Function: void gcry_mpi_sub_ui (gcry_mpi_t W, gcry_mpi_t U,
unsigned long V)
W = U - V. V is an unsigned integer.
-- Function: void gcry_mpi_subm (gcry_mpi_t W, gcry_mpi_t U,
gcry_mpi_t V, gcry_mpi_t M)
W = U - V \bmod M.
-- Function: void gcry_mpi_mul (gcry_mpi_t W, gcry_mpi_t U,
gcry_mpi_t V)
W = U * V.
-- Function: void gcry_mpi_mul_ui (gcry_mpi_t W, gcry_mpi_t U,
unsigned long V)
W = U * V. V is an unsigned integer.
-- Function: void gcry_mpi_mulm (gcry_mpi_t W, gcry_mpi_t U,
gcry_mpi_t V, gcry_mpi_t M)
W = U * V \bmod M.
-- Function: void gcry_mpi_mul_2exp (gcry_mpi_t W, gcry_mpi_t U,
unsigned long E)
W = U * 2^e.
-- Function: void gcry_mpi_div (gcry_mpi_t Q, gcry_mpi_t R,
gcry_mpi_t DIVIDEND, gcry_mpi_t DIVISOR, int ROUND)
Q = DIVIDEND / DIVISOR, R = DIVIDEND \bmod DIVISOR. Q and R may
be passed as `NULL'. ROUND should be negative or 0.
-- Function: void gcry_mpi_mod (gcry_mpi_t R, gcry_mpi_t DIVIDEND,
gcry_mpi_t DIVISOR)
R = DIVIDEND \bmod DIVISOR.
-- Function: void gcry_mpi_powm (gcry_mpi_t W, const gcry_mpi_t B,
const gcry_mpi_t E, const gcry_mpi_t M)
W = B^e \bmod M.
-- Function: int gcry_mpi_gcd (gcry_mpi_t G, gcry_mpi_t A,
gcry_mpi_t B)
Set G to the greatest common divisor of A and B. Return true if
the G is 1.
-- Function: int gcry_mpi_invm (gcry_mpi_t X, gcry_mpi_t A,
gcry_mpi_t M)
Set X to the multiplicative inverse of A \bmod M. Return true if
the inverse exists.

File: gcrypt.info, Node: Comparisons, Next: Bit manipulations, Prev: Calculations, Up: MPI library
12.5 Comparisons
================
The next 2 functions are used to compare MPIs:
-- Function: int gcry_mpi_cmp (const gcry_mpi_t U, const gcry_mpi_t V)
Compare the multi-precision-integers number U and V returning 0
for equality, a positive value for U > V and a negative for U < V.
If both numbers are opaque values (cf, gcry_mpi_set_opaque) the
comparison is done by checking the bit sizes using memcmp. If
only one number is an opaque value, the opaque value is less than
the other number.
-- Function: int gcry_mpi_cmp_ui (const gcry_mpi_t U, unsigned long V)
Compare the multi-precision-integers number U with the unsigned
integer V returning 0 for equality, a positive value for U > V and
a negative for U < V.
-- Function: int gcry_mpi_is_neg (const gcry_mpi_t A)
Return 1 if A is less than zero; return 0 if zero or positive.

File: gcrypt.info, Node: Bit manipulations, Next: EC functions, Prev: Comparisons, Up: MPI library
12.6 Bit manipulations
======================
There are a couple of functions to get information on arbitrary bits in
an MPI and to set or clear them:
-- Function: unsigned int gcry_mpi_get_nbits (gcry_mpi_t A)
Return the number of bits required to represent A.
-- Function: int gcry_mpi_test_bit (gcry_mpi_t A, unsigned int N)
Return true if bit number N (counting from 0) is set in A.
-- Function: void gcry_mpi_set_bit (gcry_mpi_t A, unsigned int N)
Set bit number N in A.
-- Function: void gcry_mpi_clear_bit (gcry_mpi_t A, unsigned int N)
Clear bit number N in A.
-- Function: void gcry_mpi_set_highbit (gcry_mpi_t A, unsigned int N)
Set bit number N in A and clear all bits greater than N.
-- Function: void gcry_mpi_clear_highbit (gcry_mpi_t A, unsigned int N)
Clear bit number N in A and all bits greater than N.
-- Function: void gcry_mpi_rshift (gcry_mpi_t X, gcry_mpi_t A,
unsigned int N)
Shift the value of A by N bits to the right and store the result
in X.
-- Function: void gcry_mpi_lshift (gcry_mpi_t X, gcry_mpi_t A,
unsigned int N)
Shift the value of A by N bits to the left and store the result in
X.

File: gcrypt.info, Node: EC functions, Next: Miscellaneous, Prev: Bit manipulations, Up: MPI library
12.7 EC functions
=================
Libgcrypt provides an API to access low level functions used by its
elliptic curve implementation. These functions allow to implement
elliptic curve methods for which no explicit support is available.
-- Function: gcry_mpi_point_t gcry_mpi_point_new (unsigned int NBITS)
Allocate a new point object, initialize it to 0, and allocate
enough memory for a points of at least NBITS. This pre-allocation
yields only a small performance win and is not really necessary
because Libgcrypt automatically re-allocates the required memory.
Using 0 for NBITS is usually the right thing to do.
-- Function: void gcry_mpi_point_release (gcry_mpi_point_t POINT)
Release POINT and free all associated resources. Passing `NULL'
is allowed and ignored.
-- Function: void gcry_mpi_point_get (gcry_mpi_t X, gcry_mpi_t Y,
gcry_mpi_t Z, gcry_mpi_point_t POINT)
Store the projective coordinates from POINT into the MPIs X, Y,
and Z. If a coordinate is not required, `NULL' may be used for X,
Y, or Z.
-- Function: void gcry_mpi_point_snatch_get (gcry_mpi_t X,
gcry_mpi_t Y, gcry_mpi_t Z, gcry_mpi_point_t POINT)
Store the projective coordinates from POINT into the MPIs X, Y,
and Z. If a coordinate is not required, `NULL' may be used for X,
Y, or Z. The object POINT is then released. Using this function
instead of `gcry_mpi_point_get' and `gcry_mpi_point_release' has
the advantage of avoiding some extra memory allocations and copies.
-- Function: gcry_mpi_point_t gcry_mpi_point_set (
gcry_mpi_point_t POINT, gcry_mpi_t X, gcry_mpi_t Y,
gcry_mpi_t Z)
Store the projective coordinates from X, Y, and Z into POINT. If
a coordinate is given as `NULL', the value 0 is used. If `NULL'
is used for POINT a new point object is allocated and returned.
Returns POINT or the newly allocated point object.
-- Function: gcry_mpi_point_t gcry_mpi_point_snatch_set (
gcry_mpi_point_t POINT, gcry_mpi_t X, gcry_mpi_t Y,
gcry_mpi_t Z)
Store the projective coordinates from X, Y, and Z into POINT. If
a coordinate is given as `NULL', the value 0 is used. If `NULL'
is used for POINT a new point object is allocated and returned.
The MPIs X, Y, and Z are released. Using this function instead of
`gcry_mpi_point_set' and 3 calls to `gcry_mpi_release' has the
advantage of avoiding some extra memory allocations and copies.
Returns POINT or the newly allocated point object.
-- Function: gpg_error_t gcry_mpi_ec_p_new (gpg_ctx_t *R_CTX,
gcry_sexp_t KEYPARAM, const char *CURVENAME)
Allocate a new context for elliptic curve operations. If KEYPARAM
is given it specifies the parameters of the curve (*note
ecc_keyparam::). If CURVENAME is given in addition to KEYPARAM
and the key parameters do not include a named curve reference, the
string CURVENAME is used to fill in missing parameters. If only
CURVENAME is given, the context is initialized for this named
curve.
If a parameter specifying a point (e.g. `g' or `q') is not found,
the parser looks for a non-encoded point by appending `.x', `.y',
and `.z' to the parameter name and looking them all up to create a
point. A parameter with the suffix `.z' is optional and defaults
to 1.
On success the function returns 0 and stores the new context
object at R_CTX; this object eventually needs to be released
(*note gcry_ctx_release::). On error the function stores `NULL' at
R_CTX and returns an error code.
-- Function: gcry_mpi_t gcry_mpi_ec_get_mpi ( const char *NAME,
gcry_ctx_t CTX, int COPY)
Return the MPI with NAME from the context CTX. If not found
`NULL' is returned. If the returned MPI may later be modified, it
is suggested to pass `1' to COPY, so that the function guarantees
that a modifiable copy of the MPI is returned. If `0' is used for
COPY, this function may return a constant flagged MPI. In any
case `gcry_mpi_release' needs to be called to release the result.
For valid names *note ecc_keyparam::. If the public key `q' is
requested but only the private key `d' is available, `q' will be
recomputed on the fly. If a point parameter is requested it is
returned as an uncompressed encoded point unless these special
names are used:
Q@EDDSA
Return an EdDSA style compressed point. This is only
supported for Twisted Edwards curves.
-- Function: gcry_mpi_point_t gcry_mpi_ec_get_point (
const char *NAME, gcry_ctx_t CTX, int COPY)
Return the point with NAME from the context CTX. If not found
`NULL' is returned. If the returned MPI may later be modified, it
is suggested to pass `1' to COPY, so that the function guarantees
that a modifiable copy of the MPI is returned. If `0' is used for
COPY, this function may return a constant flagged point. In any
case `gcry_mpi_point_release' needs to be called to release the
result. If the public key `q' is requested but only the private
key `d' is available, `q' will be recomputed on the fly.
-- Function: gpg_error_t gcry_mpi_ec_set_mpi ( const char *NAME,
gcry_mpi_t NEWVALUE, gcry_ctx_t CTX)
Store the MPI NEWVALUE at NAME into the context CTX. On success
`0' is returned; on error an error code. Valid names are the MPI
parameters of an elliptic curve (*note ecc_keyparam::).
-- Function: gpg_error_t gcry_mpi_ec_set_point ( const char *NAME,
gcry_mpi_point_t NEWVALUE, gcry_ctx_t CTX)
Store the point NEWVALUE at NAME into the context CTX. On success
`0' is returned; on error an error code. Valid names are the
point parameters of an elliptic curve (*note ecc_keyparam::).
-- Function: int gcry_mpi_ec_get_affine ( gcry_mpi_t X, gcry_mpi_t Y,
gcry_mpi_point_t POINT, gcry_ctx_t CTX)
Compute the affine coordinates from the projective coordinates in
POINT and store them into X and Y. If one coordinate is not
required, `NULL' may be passed to X or Y. CTX is the context
object which has been created using `gcry_mpi_ec_new'. Returns 0
on success or not 0 if POINT is at infinity.
Note that you can use `gcry_mpi_ec_set_point' with the value
`GCRYMPI_CONST_ONE' for Z to convert affine coordinates back into
projective coordinates.
-- Function: void gcry_mpi_ec_dup ( gcry_mpi_point_t W,
gcry_mpi_point_t U, gcry_ctx_t CTX)
Double the point U of the elliptic curve described by CTX and
store the result into W.
-- Function: void gcry_mpi_ec_add ( gcry_mpi_point_t W,
gcry_mpi_point_t U, gcry_mpi_point_t V, gcry_ctx_t CTX)
Add the points U and V of the elliptic curve described by CTX and
store the result into W.
-- Function: void gcry_mpi_ec_mul ( gcry_mpi_point_t W, gcry_mpi_t N,
gcry_mpi_point_t U, gcry_ctx_t CTX)
Multiply the point U of the elliptic curve described by CTX by N
and store the result into W.
-- Function: int gcry_mpi_ec_curve_point ( gcry_mpi_point_t POINT,
gcry_ctx_t CTX)
Return true if POINT is on the elliptic curve described by CTX.

File: gcrypt.info, Node: Miscellaneous, Prev: EC functions, Up: MPI library
12.8 Miscellaneous
==================
An MPI data type is allowed to be "misused" to store an arbitrary
value. Two functions implement this kludge:
-- Function: gcry_mpi_t gcry_mpi_set_opaque (gcry_mpi_t A, void *P,
unsigned int NBITS)
Store NBITS of the value P points to in A and mark A as an opaque
value (i.e. an value that can't be used for any math calculation
and is only used to store an arbitrary bit pattern in A).
Ownership of P is taken by this function and thus the user may not
use dereference the passed value anymore. It is required that
them memory referenced by P has been allocated in a way that
`gcry_free' is able to release it.
WARNING: Never use an opaque MPI for actual math operations. The
only valid functions are gcry_mpi_get_opaque and gcry_mpi_release.
Use gcry_mpi_scan to convert a string of arbitrary bytes into an
MPI.
-- Function: gcry_mpi_t gcry_mpi_set_opaque_copy (gcry_mpi_t A,
const void *P, unsigned int NBITS)
Same as `gcry_mpi_set_opaque' but ownership of P is not taken
instead a copy of P is used.
-- Function: void * gcry_mpi_get_opaque (gcry_mpi_t A,
unsigned int *NBITS)
Return a pointer to an opaque value stored in A and return its
size in NBITS. Note that the returned pointer is still owned by A
and that the function should never be used for an non-opaque MPI.
Each MPI has an associated set of flags for special purposes. The
currently defined flags are:
`GCRYMPI_FLAG_SECURE'
Setting this flag converts A into an MPI stored in "secure
memory". Clearing this flag is not allowed.
`GCRYMPI_FLAG_OPAQUE'
This is an interanl flag, indicating the an opaque valuue and not
an integer is stored. This is an read-only flag; it may not be
set or cleared.
`GCRYMPI_FLAG_IMMUTABLE'
If this flag is set, the MPI is marked as immutable. Setting or
changing the value of that MPI is ignored and an error message is
logged. The flag is sometimes useful for debugging.
`GCRYMPI_FLAG_CONST'
If this flag is set, the MPI is marked as a constant and as
immutable Setting or changing the value of that MPI is ignored and
an error message is logged. Such an MPI will never be deallocated
and may thus be used without copying. Note that using
gcry_mpi_copy will return a copy of that constant with this and
the immutable flag cleared. A few commonly used constants are
pre-defined and accessible using the macros `GCRYMPI_CONST_ONE',
`GCRYMPI_CONST_TWO', `GCRYMPI_CONST_THREE', `GCRYMPI_CONST_FOUR',
and `GCRYMPI_CONST_EIGHT'.
`GCRYMPI_FLAG_USER1'
`GCRYMPI_FLAG_USER2'
`GCRYMPI_FLAG_USER3'
`GCRYMPI_FLAG_USER4'
These flags are reserved for use by the application.
-- Function: void gcry_mpi_set_flag (gcry_mpi_t A,
enum gcry_mpi_flag FLAG)
Set the FLAG for the MPI A. The only allowed flags are
`GCRYMPI_FLAG_SECURE', `GCRYMPI_FLAG_IMMUTABLE', and
`GCRYMPI_FLAG_CONST'.
-- Function: void gcry_mpi_clear_flag (gcry_mpi_t A,
enum gcry_mpi_flag FLAG)
Clear FLAG for the multi-precision-integers A. The only allowed
flag is `GCRYMPI_FLAG_IMMUTABLE' but only if `GCRYMPI_FLAG_CONST'
is not set. If `GCRYMPI_FLAG_CONST' is set, clearing
`GCRYMPI_FLAG_IMMUTABLE' will simply be ignored.
o
-- Function: int gcry_mpi_get_flag (gcry_mpi_t A,
enum gcry_mpi_flag FLAG)
Return true if FLAG is set for A.
To put a random value into an MPI, the following convenience function
may be used:
-- Function: void gcry_mpi_randomize (gcry_mpi_t W,
unsigned int NBITS, enum gcry_random_level LEVEL)
Set the multi-precision-integers W to a random non-negative number
of NBITS, using random data quality of level LEVEL. In case NBITS
is not a multiple of a byte, NBITS is rounded up to the next byte
boundary. When using a LEVEL of `GCRY_WEAK_RANDOM' this function
makes use of `gcry_create_nonce'.

File: gcrypt.info, Node: Prime numbers, Next: Utilities, Prev: MPI library, Up: Top
13 Prime numbers
****************
* Menu:
* Generation:: Generation of new prime numbers.
* Checking:: Checking if a given number is prime.

File: gcrypt.info, Node: Generation, Next: Checking, Up: Prime numbers
13.1 Generation
===============
-- Function: gcry_error_t gcry_prime_generate (gcry_mpi_t
*PRIME,unsigned int PRIME_BITS, unsigned int FACTOR_BITS,
gcry_mpi_t **FACTORS, gcry_prime_check_func_t CB_FUNC, void
*CB_ARG, gcry_random_level_t RANDOM_LEVEL, unsigned int FLAGS)
Generate a new prime number of PRIME_BITS bits and store it in
PRIME. If FACTOR_BITS is non-zero, one of the prime factors of
(PRIME - 1) / 2 must be FACTOR_BITS bits long. If FACTORS is
non-zero, allocate a new, `NULL'-terminated array holding the
prime factors and store it in FACTORS. FLAGS might be used to
influence the prime number generation process.
-- Function: gcry_error_t gcry_prime_group_generator (gcry_mpi_t *R_G,
gcry_mpi_t PRIME, gcry_mpi_t *FACTORS, gcry_mpi_t START_G)
Find a generator for PRIME where the factorization of (PRIME-1) is
in the `NULL' terminated array FACTORS. Return the generator as a
newly allocated MPI in R_G. If START_G is not NULL, use this as
the start for the search.
-- Function: void gcry_prime_release_factors (gcry_mpi_t *FACTORS)
Convenience function to release the FACTORS array.

File: gcrypt.info, Node: Checking, Prev: Generation, Up: Prime numbers
13.2 Checking
=============
-- Function: gcry_error_t gcry_prime_check (gcry_mpi_t P, unsigned int
FLAGS)
Check whether the number P is prime. Returns zero in case P is
indeed a prime, returns `GPG_ERR_NO_PRIME' in case P is not a
prime and a different error code in case something went horribly
wrong.

File: gcrypt.info, Node: Utilities, Next: Tools, Prev: Prime numbers, Up: Top
14 Utilities
************
* Menu:
* Memory allocation:: Functions related with memory allocation.
* Context management:: Functions related with context management.
* Buffer description:: A data type to describe buffers.

File: gcrypt.info, Node: Memory allocation, Next: Context management, Up: Utilities
14.1 Memory allocation
======================
-- Function: void * gcry_malloc (size_t N)
This function tries to allocate N bytes of memory. On success it
returns a pointer to the memory area, in an out-of-core condition,
it returns NULL.
-- Function: void * gcry_malloc_secure (size_t N)
Like `gcry_malloc', but uses secure memory.
-- Function: void * gcry_calloc (size_t N, size_t M)
This function allocates a cleared block of memory (i.e.
initialized with zero bytes) long enough to contain a vector of N
elements, each of size M bytes. On success it returns a pointer
to the memory block; in an out-of-core condition, it returns NULL.
-- Function: void * gcry_calloc_secure (size_t N, size_t M)
Like `gcry_calloc', but uses secure memory.
-- Function: void * gcry_realloc (void *P, size_t N)
This function tries to resize the memory area pointed to by P to N
bytes. On success it returns a pointer to the new memory area, in
an out-of-core condition, it returns NULL. Depending on whether
the memory pointed to by P is secure memory or not, gcry_realloc
tries to use secure memory as well.
-- Function: void gcry_free (void *P)
Release the memory area pointed to by P.

File: gcrypt.info, Node: Context management, Next: Buffer description, Prev: Memory allocation, Up: Utilities
14.2 Context management
=======================
Some function make use of a context object. As of now there are only a
few math functions. However, future versions of Libgcrypt may make more
use of this context object.
-- Data type: gcry_ctx_t
This type is used to refer to the general purpose context object.
-- Function: void gcry_ctx_release (gcry_ctx_t CTX)
Release the context object CTX and all associated resources. A
`NULL' passed as CTX is ignored.

File: gcrypt.info, Node: Buffer description, Prev: Context management, Up: Utilities
14.3 Buffer description
=======================
To help hashing non-contiguous areas of memory a general purpose data
type is defined:
-- Data type: gcry_buffer_t
This type is a structure to describe a buffer. The user should
make sure that this structure is initialized to zero. The
available fields of this structure are:
`.size'
This is either 0 for no information available or indicates the
allocated length of the buffer.
`.off'
This is the offset into the buffer.
`.len'
This is the valid length of the buffer starting at `.off'.
`.data'
This is the address of the buffer.

File: gcrypt.info, Node: Tools, Next: Architecture, Prev: Utilities, Up: Top
15 Tools
********
* Menu:
* hmac256:: A standalone HMAC-SHA-256 implementation

File: gcrypt.info, Node: hmac256, Up: Tools
15.1 A HMAC-SHA-256 tool
========================
This is a standalone HMAC-SHA-256 implementation used to compute an
HMAC-SHA-256 message authentication code. The tool has originally been
developed as a second implementation for Libgcrypt to allow comparing
against the primary implementation and to be used for internal
consistency checks. It should not be used for sensitive data because
no mechanisms to clear the stack etc are used.
The code has been written in a highly portable manner and requires
only a few standard definitions to be provided in a config.h file.
`hmac256' is commonly invoked as
hmac256 "This is my key" foo.txt
This compute the MAC on the file `foo.txt' using the key given on the
command line.
`hmac256' understands these options:
`--binary'
Print the MAC as a binary string. The default is to print the MAC
encoded has lower case hex digits.
`--version'
Print version of the program and exit.

File: gcrypt.info, Node: Architecture, Next: Self-Tests, Prev: Tools, Up: Top
16 Architecture
***************
This chapter describes the internal architecture of Libgcrypt.
Libgcrypt is a function library written in ISO C-90. Any compliant
compiler should be able to build Libgcrypt as long as the target is
either a POSIX platform or compatible to the API used by Windows NT.
Provisions have been take so that the library can be directly used from
C++ applications; however building with a C++ compiler is not supported.
Building Libgcrypt is done by using the common `./configure && make'
approach. The configure command is included in the source distribution
and as a portable shell script it works on any Unix-alike system. The
result of running the configure script are a C header file
(`config.h'), customized Makefiles, the setup of symbolic links and a
few other things. After that the make tool builds and optionally
installs the library and the documentation. See the files `INSTALL'
and `README' in the source distribution on how to do this.
Libgcrypt is developed using a Subversion(1) repository. Although
all released versions are tagged in this repository, they should not be
used to build production versions of Libgcrypt. Instead released
tarballs should be used. These tarballs are available from several
places with the master copy at <ftp://ftp.gnupg.org/gcrypt/libgcrypt/>.
Announcements of new releases are posted to the
<gnupg-announce@gnupg.org> mailing list(2).
�[image src="libgcrypt-modules.png" alt="Libgcrypt subsystems"�]
Figure 16.1: Libgcrypt subsystems
Libgcrypt consists of several subsystems (*note Figure 16.1:
fig:subsystems.) and all these subsystems provide a public API; this
includes the helper subsystems like the one for S-expressions. The API
style depends on the subsystem; in general an open-use-close approach
is implemented. The open returns a handle to a context used for all
further operations on this handle, several functions may then be used
on this handle and a final close function releases all resources
associated with the handle.
* Menu:
* Public-Key Subsystem Architecture:: About public keys.
* Symmetric Encryption Subsystem Architecture:: About standard ciphers.
* Hashing and MACing Subsystem Architecture:: About hashing.
* Multi-Precision-Integer Subsystem Architecture:: About big integers.
* Prime-Number-Generator Subsystem Architecture:: About prime numbers.
* Random-Number Subsystem Architecture:: About random stuff.
---------- Footnotes ----------
(1) A version control system available for many platforms
(2) See `http://www.gnupg.org/documentation/mailing-lists.en.html'
for details.

File: gcrypt.info, Node: Public-Key Subsystem Architecture, Next: Symmetric Encryption Subsystem Architecture, Up: Architecture
16.1 Public-Key Architecture
============================
Because public key cryptography is almost always used to process small
amounts of data (hash values or session keys), the interface is not
implemented using the open-use-close paradigm, but with single
self-contained functions. Due to the wide variety of parameters
required by different algorithms S-expressions, as flexible way to
convey these parameters, are used. There is a set of helper functions
to work with these S-expressions.
Aside of functions to register new algorithms, map algorithms names
to algorithms identifiers and to lookup properties of a key, the
following main functions are available:
`gcry_pk_encrypt'
Encrypt data using a public key.
`gcry_pk_decrypt'
Decrypt data using a private key.
`gcry_pk_sign'
Sign data using a private key.
`gcry_pk_verify'
Verify that a signature matches the data.
`gcry_pk_testkey'
Perform a consistency over a public or private key.
`gcry_pk_genkey'
Create a new public/private key pair.
All these functions lookup the module implementing the algorithm and
pass the actual work to that module. The parsing of the S-expression
input and the construction of S-expression for the return values is
done by the high level code (`cipher/pubkey.c'). Thus the internal
interface between the algorithm modules and the high level functions
passes data in a custom format.
By default Libgcrypt uses a blinding technique for RSA decryption to
mitigate real world timing attacks over a network: Instead of using the
RSA decryption directly, a blinded value y = x r^e \bmod n is decrypted
and the unblinded value x' = y' r^-1 \bmod n returned. The blinding
value r is a random value with the size of the modulus n and generated
with `GCRY_WEAK_RANDOM' random level.
The algorithm used for RSA and DSA key generation depends on whether
Libgcrypt is operated in standard or in FIPS mode. In standard mode an
algorithm based on the Lim-Lee prime number generator is used. In FIPS
mode RSA keys are generated as specified in ANSI X9.31 (1998) and DSA
keys as specified in FIPS 186-2.

File: gcrypt.info, Node: Symmetric Encryption Subsystem Architecture, Next: Hashing and MACing Subsystem Architecture, Prev: Public-Key Subsystem Architecture, Up: Architecture
16.2 Symmetric Encryption Subsystem Architecture
================================================
The interface to work with symmetric encryption algorithms is made up
of functions from the `gcry_cipher_' name space. The implementation
follows the open-use-close paradigm and uses registered algorithm
modules for the actual work. Unless a module implements optimized
cipher mode implementations, the high level code (`cipher/cipher.c')
implements the modes and calls the core algorithm functions to process
each block.
The most important functions are:
`gcry_cipher_open'
Create a new instance to encrypt or decrypt using a specified
algorithm and mode.
`gcry_cipher_close'
Release an instance.
`gcry_cipher_setkey'
Set a key to be used for encryption or decryption.
`gcry_cipher_setiv'
Set an initialization vector to be used for encryption or
decryption.
`gcry_cipher_encrypt'
`gcry_cipher_decrypt'
Encrypt or decrypt data. These functions may be called with
arbitrary amounts of data and as often as needed to encrypt or
decrypt all data.
There are also functions to query properties of algorithms or
context, like block length, key length, map names or to enable features
like padding methods.

File: gcrypt.info, Node: Hashing and MACing Subsystem Architecture, Next: Multi-Precision-Integer Subsystem Architecture, Prev: Symmetric Encryption Subsystem Architecture, Up: Architecture
16.3 Hashing and MACing Subsystem Architecture
==============================================
The interface to work with message digests and CRC algorithms is made
up of functions from the `gcry_md_' name space. The implementation
follows the open-use-close paradigm and uses registered algorithm
modules for the actual work. Although CRC algorithms are not
considered cryptographic hash algorithms, they share enough properties
so that it makes sense to handle them in the same way. It is possible
to use several algorithms at once with one context and thus compute
them all on the same data.
The most important functions are:
`gcry_md_open'
Create a new message digest instance and optionally enable one
algorithm. A flag may be used to turn the message digest algorithm
into a HMAC algorithm.
`gcry_md_enable'
Enable an additional algorithm for the instance.
`gcry_md_setkey'
Set the key for the MAC.
`gcry_md_write'
Pass more data for computing the message digest to an instance.
`gcry_md_putc'
Buffered version of `gcry_md_write' implemented as a macro.
`gcry_md_read'
Finalize the computation of the message digest or HMAC and return
the result.
`gcry_md_close'
Release an instance
`gcry_md_hash_buffer'
Convenience function to directly compute a message digest over a
memory buffer without the need to create an instance first.
There are also functions to query properties of algorithms or the
instance, like enabled algorithms, digest length, map algorithm names.
it is also possible to reset an instance or to copy the current state
of an instance at any time. Debug functions to write the hashed data
to files are available as well.

File: gcrypt.info, Node: Multi-Precision-Integer Subsystem Architecture, Next: Prime-Number-Generator Subsystem Architecture, Prev: Hashing and MACing Subsystem Architecture, Up: Architecture
16.4 Multi-Precision-Integer Subsystem Architecture
===================================================
The implementation of Libgcrypt's big integer computation code is based
on an old release of GNU Multi-Precision Library (GMP). The decision
not to use the GMP library directly was due to stalled development at
that time and due to security requirements which could not be provided
by the code in GMP. As GMP does, Libgcrypt provides high performance
assembler implementations of low level code for several CPUS to gain
much better performance than with a generic C implementation.
Major features of Libgcrypt's multi-precision-integer code compared to
GMP are:
* Avoidance of stack based allocations to allow protection against
swapping out of sensitive data and for easy zeroing of sensitive
intermediate results.
* Optional use of secure memory and tracking of its use so that
results are also put into secure memory.
* MPIs are identified by a handle (implemented as a pointer) to give
better control over allocations and to augment them with extra
properties like opaque data.
* Removal of unnecessary code to reduce complexity.
* Functions specialized for public key cryptography.

File: gcrypt.info, Node: Prime-Number-Generator Subsystem Architecture, Next: Random-Number Subsystem Architecture, Prev: Multi-Precision-Integer Subsystem Architecture, Up: Architecture
16.5 Prime-Number-Generator Subsystem Architecture
==================================================
Libgcrypt provides an interface to its prime number generator. These
functions make use of the internal prime number generator which is
required for the generation for public key key pairs. The plain prime
checking function is exported as well.
The generation of random prime numbers is based on the Lim and Lee
algorithm to create practically save primes.(1) This algorithm creates
a pool of smaller primes, select a few of them to create candidate
primes of the form 2 * p_0 * p_1 * ... * p_n + 1, tests the candidate
for primality and permutates the pool until a prime has been found. It
is possible to clamp one of the small primes to a certain size to help
DSA style algorithms. Because most of the small primes in the pool are
not used for the resulting prime number, they are saved for later use
(see `save_pool_prime' and `get_pool_prime' in `cipher/primegen.c').
The prime generator optionally supports the finding of an appropriate
generator.
The primality test works in three steps:
1. The standard sieve algorithm using the primes up to 4999 is used
as a quick first check.
2. A Fermat test filters out almost all non-primes.
3. A 5 round Rabin-Miller test is finally used. The first round uses
a witness of 2, whereas the next rounds use a random witness.
To support the generation of RSA and DSA keys in FIPS mode according
to X9.31 and FIPS 186-2, Libgcrypt implements two additional prime
generation functions: `_gcry_derive_x931_prime' and
`_gcry_generate_fips186_2_prime'. These functions are internal and not
available through the public API.
---------- Footnotes ----------
(1) Chae Hoon Lim and Pil Joong Lee. A key recovery attack on
discrete log-based schemes using a prime order subgroup. In Burton S.
Kaliski Jr., editor, Advances in Cryptology: Crypto '97, pages
249­-263, Berlin / Heidelberg / New York, 1997. Springer-Verlag.
Described on page 260.

File: gcrypt.info, Node: Random-Number Subsystem Architecture, Prev: Prime-Number-Generator Subsystem Architecture, Up: Architecture
16.6 Random-Number Subsystem Architecture
=========================================
Libgcrypt provides 3 levels or random quality: The level
`GCRY_VERY_STRONG_RANDOM' usually used for key generation, the level
`GCRY_STRONG_RANDOM' for all other strong random requirements and the
function `gcry_create_nonce' which is used for weaker usages like
nonces. There is also a level `GCRY_WEAK_RANDOM' which in general maps
to `GCRY_STRONG_RANDOM' except when used with the function
`gcry_mpi_randomize', where it randomizes an multi-precision-integer
using the `gcry_create_nonce' function.
There are two distinct random generators available:
* The Continuously Seeded Pseudo Random Number Generator (CSPRNG),
which is based on the classic GnuPG derived big pool
implementation. Implemented in `random/random-csprng.c' and used
by default.
* A FIPS approved ANSI X9.31 PRNG using AES with a 128 bit key.
Implemented in `random/random-fips.c' and used if Libgcrypt is in
FIPS mode.
Both generators make use of so-called entropy gathering modules:
rndlinux
Uses the operating system provided `/dev/random' and
`/dev/urandom' devices.
rndunix
Runs several operating system commands to collect entropy from
sources like virtual machine and process statistics. It is a kind
of poor-man's `/dev/random' implementation. It is not available in
FIPS mode.
rndegd
Uses the operating system provided Entropy Gathering Daemon (EGD).
The EGD basically uses the same algorithms as rndunix does.
However as a system daemon it keeps on running and thus can serve
several processes requiring entropy input and does not waste
collected entropy if the application does not need all the
collected entropy. It is not available in FIPS mode.
rndw32
Targeted for the Microsoft Windows OS. It uses certain properties
of that system and is the only gathering module available for that
OS.
rndhw
Extra module to collect additional entropy by utilizing a hardware
random number generator. As of now the only supported hardware
RNG is the Padlock engine of VIA (Centaur) CPUs. It is not
available in FIPS mode.
* Menu:
* CSPRNG Description:: Description of the CSPRNG.
* FIPS PRNG Description:: Description of the FIPS X9.31 PRNG.

File: gcrypt.info, Node: CSPRNG Description, Next: FIPS PRNG Description, Up: Random-Number Subsystem Architecture
16.6.1 Description of the CSPRNG
--------------------------------
This random number generator is loosely modelled after the one
described in Peter Gutmann's paper: "Software Generation of Practically
Strong Random Numbers".(1)
A pool of 600 bytes is used and mixed using the core RIPE-MD160 hash
transform function. Several extra features are used to make the robust
against a wide variety of attacks and to protect against failures of
subsystems. The state of the generator may be saved to a file and
initially seed form a file.
Depending on how Libgcrypt was build the generator is able to select
the best working entropy gathering module. It makes use of the slow
and fast collection methods and requires the pool to initially seeded
form the slow gatherer or a seed file. An entropy estimation is used
to mix in enough data from the gather modules before returning the
actual random output. Process fork detection and protection is
implemented.
The implementation of the nonce generator (for `gcry_create_nonce')
is a straightforward repeated hash design: A 28 byte buffer is
initially seeded with the PID and the time in seconds in the first 20
bytes and with 8 bytes of random taken from the `GCRY_STRONG_RANDOM'
generator. Random numbers are then created by hashing all the 28 bytes
with SHA-1 and saving that again in the first 20 bytes. The hash is
also returned as result.
---------- Footnotes ----------
(1) Also described in chapter 6 of his book "Cryptographic Security
Architecture", New York, 2004, ISBN 0-387-95387-6.

File: gcrypt.info, Node: FIPS PRNG Description, Prev: CSPRNG Description, Up: Random-Number Subsystem Architecture
16.6.2 Description of the FIPS X9.31 PRNG
-----------------------------------------
The core of this deterministic random number generator is implemented
according to the document "NIST-Recommended Random Number Generator
Based on ANSI X9.31 Appendix A.2.4 Using the 3-Key Triple DES and AES
Algorithms", dated 2005-01-31. This implementation uses the AES
variant.
The generator is based on contexts to utilize the same core functions
for all random levels as required by the high-level interface. All
random generators return their data in 128 bit blocks. If the caller
requests less bits, the extra bits are not used. The key for each
generator is only set once at the first time a generator context is
used. The seed value is set along with the key and again after 1000
output blocks.
On Unix like systems the `GCRY_VERY_STRONG_RANDOM' and
`GCRY_STRONG_RANDOM' generators are keyed and seeded using the rndlinux
module with the `/dev/random' device. Thus these generators may block
until the OS kernel has collected enough entropy. When used with
Microsoft Windows the rndw32 module is used instead.
The generator used for `gcry_create_nonce' is keyed and seeded from
the `GCRY_STRONG_RANDOM' generator. Thus is may also block if the
`GCRY_STRONG_RANDOM' generator has not yet been used before and thus
gets initialized on the first use by `gcry_create_nonce'. This special
treatment is justified by the weaker requirements for a nonce generator
and to save precious kernel entropy for use by the "real" random
generators.
A self-test facility uses a separate context to check the
functionality of the core X9.31 functions using a known answers test.
During runtime each output block is compared to the previous one to
detect a stuck generator.
The DT value for the generator is made up of the current time down to
microseconds (if available) and a free running 64 bit counter. When
used with the test context the DT value is taken from the context and
incremented on each use.

File: gcrypt.info, Node: Self-Tests, Next: FIPS Mode, Prev: Architecture, Up: Top
Appendix A Description of the Self-Tests
****************************************
In addition to the build time regression test suite, Libgcrypt
implements self-tests to be performed at runtime. Which self-tests are
actually used depends on the mode Libgcrypt is used in. In standard
mode a limited set of self-tests is run at the time an algorithm is
first used. Note that not all algorithms feature a self-test in
standard mode. The `GCRYCTL_SELFTEST' control command may be used to
run all implemented self-tests at any time; this will even run more
tests than those run in FIPS mode.
If any of the self-tests fails, the library immediately returns an
error code to the caller. If Libgcrypt is in FIPS mode the self-tests
will be performed within the "Self-Test" state and any failure puts the
library into the "Error" state.
A.1 Power-Up Tests
==================
Power-up tests are only performed if Libgcrypt is in FIPS mode.
A.1.1 Symmetric Cipher Algorithm Power-Up Tests
-----------------------------------------------
The following symmetric encryption algorithm tests are run during
power-up:
3DES
To test the 3DES 3-key EDE encryption in ECB mode these tests are
run:
1. A known answer test is run on a 64 bit test vector processed
by 64 rounds of Single-DES block encryption and decryption
using a key changed with each round.
2. A known answer test is run on a 64 bit test vector processed
by 16 rounds of 2-key and 3-key Triple-DES block encryption
and decryptions using a key changed with each round.
3. 10 known answer tests using 3-key Triple-DES EDE encryption,
comparing the ciphertext to the known value, then running a
decryption and comparing it to the initial plaintext.
(`cipher/des.c:selftest')
AES-128
A known answer tests is run using one test vector and one test key
with AES in ECB mode. (`cipher/rijndael.c:selftest_basic_128')
AES-192
A known answer tests is run using one test vector and one test key
with AES in ECB mode. (`cipher/rijndael.c:selftest_basic_192')
AES-256
A known answer tests is run using one test vector and one test key
with AES in ECB mode. (`cipher/rijndael.c:selftest_basic_256')
A.1.2 Hash Algorithm Power-Up Tests
-----------------------------------
The following hash algorithm tests are run during power-up:
SHA-1
A known answer test using the string `"abc"' is run.
(`cipher/sha1.c:selftests_sha1')
SHA-224
A known answer test using the string `"abc"' is run.
(`cipher/sha256.c:selftests_sha224')
SHA-256
A known answer test using the string `"abc"' is run.
(`cipher/sha256.c:selftests_sha256')
SHA-384
A known answer test using the string `"abc"' is run.
(`cipher/sha512.c:selftests_sha384')
SHA-512
A known answer test using the string `"abc"' is run.
(`cipher/sha512.c:selftests_sha512')
A.1.3 MAC Algorithm Power-Up Tests
----------------------------------
The following MAC algorithm tests are run during power-up:
HMAC SHA-1
A known answer test using 9 byte of data and a 64 byte key is run.
(`cipher/hmac-tests.c:selftests_sha1')
HMAC SHA-224
A known answer test using 28 byte of data and a 4 byte key is run.
(`cipher/hmac-tests.c:selftests_sha224')
HMAC SHA-256
A known answer test using 28 byte of data and a 4 byte key is run.
(`cipher/hmac-tests.c:selftests_sha256')
HMAC SHA-384
A known answer test using 28 byte of data and a 4 byte key is run.
(`cipher/hmac-tests.c:selftests_sha384')
HMAC SHA-512
A known answer test using 28 byte of data and a 4 byte key is run.
(`cipher/hmac-tests.c:selftests_sha512')
A.1.4 Random Number Power-Up Test
---------------------------------
The DRNG is tested during power-up this way:
1. Requesting one block of random using the public interface to check
general working and the duplicated block detection.
2. 3 know answer tests using pre-defined keys, seed and initial DT
values. For each test 3 blocks of 16 bytes are requested and
compared to the expected result. The DT value is incremented for
each block.
A.1.5 Public Key Algorithm Power-Up Tests
-----------------------------------------
The public key algorithms are tested during power-up:
RSA
A pre-defined 1024 bit RSA key is used and these tests are run in
turn:
1. Conversion of S-expression to internal format.
(`cipher/rsa.c:selftests_rsa')
2. Private key consistency check. (`cipher/rsa.c:selftests_rsa')
3. A pre-defined 20 byte value is signed with PKCS#1 padding for
SHA-1. The result is verified using the public key against
the original data and against modified data.
(`cipher/rsa.c:selftest_sign_1024')
4. A 1000 bit random value is encrypted and checked that it does
not match the original random value. The encrypted result is
then decrypted and checked that it matches the original
random value. (`cipher/rsa.c:selftest_encr_1024')
DSA
A pre-defined 1024 bit DSA key is used and these tests are run in
turn:
1. Conversion of S-expression to internal format.
(`cipher/dsa.c:selftests_dsa')
2. Private key consistency check. (`cipher/dsa.c:selftests_dsa')
3. A pre-defined 20 byte value is signed with PKCS#1 padding for
SHA-1. The result is verified using the public key against
the original data and against modified data.
(`cipher/dsa.c:selftest_sign_1024')
A.1.6 Integrity Power-Up Tests
------------------------------
The integrity of the Libgcrypt is tested during power-up but only if
checking has been enabled at build time. The check works by computing
a HMAC SHA-256 checksum over the file used to load Libgcrypt into
memory. That checksum is compared against a checksum stored in a file
of the same name but with a single dot as a prefix and a suffix of
`.hmac'.
A.1.7 Critical Functions Power-Up Tests
---------------------------------------
The 3DES weak key detection is tested during power-up by calling the
detection function with keys taken from a table listening all weak
keys. The table itself is protected using a SHA-1 hash.
(`cipher/des.c:selftest')
A.2 Conditional Tests
=====================
The conditional tests are performed if a certain condition is met.
This may occur at any time; the library does not necessary enter the
"Self-Test" state to run these tests but will transit to the "Error"
state if a test failed.
A.2.1 Key-Pair Generation Tests
-------------------------------
After an asymmetric key-pair has been generated, Libgcrypt runs a
pair-wise consistency tests on the generated key. On failure the
generated key is not used, an error code is returned and, if in FIPS
mode, the library is put into the "Error" state.
RSA
The test uses a random number 64 bits less the size of the modulus
as plaintext and runs an encryption and decryption operation in
turn. The encrypted value is checked to not match the plaintext
and the result of the decryption is checked to match the plaintext.
A new random number of the same size is generated, signed and
verified to test the correctness of the signing operation. As a
second signing test, the signature is modified by incrementing its
value and then verified with the expected result that the
verification fails. (`cipher/rsa.c:test_keys')
DSA
The test uses a random number of the size of the Q parameter to
create a signature and then checks that the signature verifies.
As a second signing test, the data is modified by incrementing its
value and then verified against the signature with the expected
result that the verification fails. (`cipher/dsa.c:test_keys')
A.2.2 Software Load Tests
-------------------------
No code is loaded at runtime.
A.2.3 Manual Key Entry Tests
----------------------------
A manual key entry feature is not implemented in Libgcrypt.
A.2.4 Continuous RNG Tests
--------------------------
The continuous random number test is only used in FIPS mode. The RNG
generates blocks of 128 bit size; the first block generated per context
is saved in the context and another block is generated to be returned
to the caller. Each block is compared against the saved block and then
stored in the context. If a duplicated block is detected an error is
signaled and the library is put into the "Fatal-Error" state.
(`random/random-fips.c:x931_aes_driver')
A.3 Application Requested Tests
===============================
The application may requests tests at any time by means of the
`GCRYCTL_SELFTEST' control command. Note that using these tests is not
FIPS conform: Although Libgcrypt rejects all application requests for
services while running self-tests, it does not ensure that no other
operations of Libgcrypt are still being executed. Thus, in FIPS mode
an application requesting self-tests needs to power-cycle Libgcrypt
instead.
When self-tests are requested, Libgcrypt runs all the tests it does
during power-up as well as a few extra checks as described below.
A.3.1 Symmetric Cipher Algorithm Tests
--------------------------------------
The following symmetric encryption algorithm tests are run in addition
to the power-up tests:
AES-128
A known answer tests with test vectors taken from NIST SP800-38a
and using the high level functions is run for block modes CFB and
OFB.
A.3.2 Hash Algorithm Tests
--------------------------
The following hash algorithm tests are run in addition to the power-up
tests:
SHA-1
SHA-224
SHA-256
1. A known answer test using a 56 byte string is run.
2. A known answer test using a string of one million letters "a"
is run.
(`cipher/sha1.c:selftests_sha1',
`cipher/sha256.c:selftests_sha224',
`cipher/sha256.c:selftests_sha256')
SHA-384
SHA-512
1. A known answer test using a 112 byte string is run.
2. A known answer test using a string of one million letters "a"
is run.
(`cipher/sha512.c:selftests_sha384',
`cipher/sha512.c:selftests_sha512')
A.3.3 MAC Algorithm Tests
-------------------------
The following MAC algorithm tests are run in addition to the power-up
tests:
HMAC SHA-1
1. A known answer test using 9 byte of data and a 20 byte key is
run.
2. A known answer test using 9 byte of data and a 100 byte key
is run.
3. A known answer test using 9 byte of data and a 49 byte key is
run.
(`cipher/hmac-tests.c:selftests_sha1')
HMAC SHA-224
HMAC SHA-256
HMAC SHA-384
HMAC SHA-512
1. A known answer test using 9 byte of data and a 20 byte key is
run.
2. A known answer test using 50 byte of data and a 20 byte key
is run.
3. A known answer test using 50 byte of data and a 26 byte key
is run.
4. A known answer test using 54 byte of data and a 131 byte key
is run.
5. A known answer test using 152 byte of data and a 131 byte key
is run.
(`cipher/hmac-tests.c:selftests_sha224',
`cipher/hmac-tests.c:selftests_sha256',
`cipher/hmac-tests.c:selftests_sha384',
`cipher/hmac-tests.c:selftests_sha512')

File: gcrypt.info, Node: FIPS Mode, Next: Library Copying, Prev: Self-Tests, Up: Top
Appendix B Description of the FIPS Mode
***************************************
This appendix gives detailed information pertaining to the FIPS mode.
In particular, the changes to the standard mode and the finite state
machine are described. The self-tests required in this mode are
described in the appendix on self-tests.
B.1 Restrictions in FIPS Mode
=============================
If Libgcrypt is used in FIPS mode these restrictions are effective:
* The cryptographic algorithms are restricted to this list:
GCRY_CIPHER_3DES
3 key EDE Triple-DES symmetric encryption.
GCRY_CIPHER_AES128
AES 128 bit symmetric encryption.
GCRY_CIPHER_AES192
AES 192 bit symmetric encryption.
GCRY_CIPHER_AES256
AES 256 bit symmetric encryption.
GCRY_MD_SHA1
SHA-1 message digest.
GCRY_MD_SHA224
SHA-224 message digest.
GCRY_MD_SHA256
SHA-256 message digest.
GCRY_MD_SHA384
SHA-384 message digest.
GCRY_MD_SHA512
SHA-512 message digest.
GCRY_MD_SHA1,GCRY_MD_FLAG_HMAC
HMAC using a SHA-1 message digest.
GCRY_MD_SHA224,GCRY_MD_FLAG_HMAC
HMAC using a SHA-224 message digest.
GCRY_MD_SHA256,GCRY_MD_FLAG_HMAC
HMAC using a SHA-256 message digest.
GCRY_MD_SHA384,GCRY_MD_FLAG_HMAC
HMAC using a SHA-384 message digest.
GCRY_MD_SHA512,GCRY_MD_FLAG_HMAC
HMAC using a SHA-512 message digest.
GCRY_PK_RSA
RSA encryption and signing.
GCRY_PK_DSA
DSA signing.
Note that the CRC algorithms are not considered cryptographic
algorithms and thus are in addition available.
* RSA key generation refuses to create a key with a keysize of less
than 1024 bits.
* DSA key generation refuses to create a key with a keysize other
than 1024 bits.
* The `transient-key' flag for RSA and DSA key generation is ignored.
* Support for the VIA Padlock engine is disabled.
* FIPS mode may only be used on systems with a /dev/random device.
Switching into FIPS mode on other systems will fail at runtime.
* Saving and loading a random seed file is ignored.
* An X9.31 style random number generator is used in place of the
large-pool-CSPRNG generator.
* The command `GCRYCTL_ENABLE_QUICK_RANDOM' is ignored.
* Message digest debugging is disabled.
* All debug output related to cryptographic data is suppressed.
* On-the-fly self-tests are not performed, instead self-tests are run
before entering operational state.
* The function `gcry_set_allocation_handler' may not be used. If it
is used Libgcrypt disables FIPS mode unless Enforced FIPS mode is
enabled, in which case Libgcrypt will enter the error state.
* The digest algorithm MD5 may not be used. If it is used Libgcrypt
disables FIPS mode unless Enforced FIPS mode is enabled, in which
case Libgcrypt will enter the error state.
* In Enforced FIPS mode the command `GCRYCTL_DISABLE_SECMEM' is
ignored. In standard FIPS mode it disables FIPS mode.
* A handler set by `gcry_set_outofcore_handler' is ignored.
* A handler set by `gcry_set_fatalerror_handler' is ignored.
Note that when we speak about disabling FIPS mode, it merely means
that the function `gcry_fips_mode_active' returns false; it does not
mean that any non FIPS algorithms are allowed.
B.2 FIPS Finite State Machine
=============================
The FIPS mode of libgcrypt implements a finite state machine (FSM) using
8 states (*note tbl:fips-states::) and checks at runtime that only valid
transitions (*note tbl:fips-state-transitions::) may happen.
�[image src="fips-fsm.png" alt="FIPS FSM Diagram"�]
Figure B.1: FIPS mode state diagram
States used by the FIPS FSM:
Power-Off
Libgcrypt is not runtime linked to another application. This
usually means that the library is not loaded into main memory.
This state is documentation only.
Power-On
Libgcrypt is loaded into memory and API calls may be made.
Compiler introduced constructor functions may be run. Note that
Libgcrypt does not implement any arbitrary constructor functions
to be called by the operating system
Init
The Libgcrypt initialization functions are performed and the
library has not yet run any self-test.
Self-Test
Libgcrypt is performing self-tests.
Operational
Libgcrypt is in the operational state and all interfaces may be
used.
Error
Libgrypt is in the error state. When calling any FIPS relevant
interfaces they either return an error (`GPG_ERR_NOT_OPERATIONAL')
or put Libgcrypt into the Fatal-Error state and won't return.
Fatal-Error
Libgcrypt is in a non-recoverable error state and will
automatically transit into the Shutdown state.
Shutdown
Libgcrypt is about to be terminated and removed from the memory.
The application may at this point still running cleanup handlers.
Table B.1: FIPS mode states
The valid state transitions (*note Figure B.1: fig:fips-fsm.) are:
`1'
Power-Off to Power-On is implicitly done by the OS loading
Libgcrypt as a shared library and having it linked to an
application.
`2'
Power-On to Init is triggered by the application calling the
Libgcrypt initialization function `gcry_check_version'.
`3'
Init to Self-Test is either triggered by a dedicated API call or
implicit by invoking a libgrypt service controlled by the FSM.
`4'
Self-Test to Operational is triggered after all self-tests passed
successfully.
`5'
Operational to Shutdown is an artificial state without any direct
action in Libgcrypt. When reaching the Shutdown state the library
is deinitialized and can't return to any other state again.
`6'
Shutdown to Power-off is the process of removing Libgcrypt from the
computer's memory. For obvious reasons the Power-Off state can't
be represented within Libgcrypt and thus this transition is for
documentation only.
`7'
Operational to Error is triggered if Libgcrypt detected an
application error which can't be returned to the caller but still
allows Libgcrypt to properly run. In the Error state all FIPS
relevant interfaces return an error code.
`8'
Error to Shutdown is similar to the Operational to Shutdown
transition (5).
`9'
Error to Fatal-Error is triggered if Libgrypt detects an fatal
error while already being in Error state.
`10'
Fatal-Error to Shutdown is automatically entered by Libgcrypt
after having reported the error.
`11'
Power-On to Shutdown is an artificial state to document that
Libgcrypt has not ye been initialized but the process is about to
terminate.
`12'
Power-On to Fatal-Error will be triggered if certain Libgcrypt
functions are used without having reached the Init state.
`13'
Self-Test to Fatal-Error is triggered by severe errors in
Libgcrypt while running self-tests.
`14'
Self-Test to Error is triggered by a failed self-test.
`15'
Operational to Fatal-Error is triggered if Libcrypt encountered a
non-recoverable error.
`16'
Operational to Self-Test is triggered if the application requested
to run the self-tests again.
`17'
Error to Self-Test is triggered if the application has requested
to run self-tests to get to get back into operational state after
an error.
`18'
Init to Error is triggered by errors in the initialization code.
`19'
Init to Fatal-Error is triggered by non-recoverable errors in the
initialization code.
`20'
Error to Error is triggered by errors while already in the Error
state.
Table B.2: FIPS mode state transitions
B.3 FIPS Miscellaneous Information
==================================
Libgcrypt does not do any key management on itself; the application
needs to care about it. Keys which are passed to Libgcrypt should be
allocated in secure memory as available with the functions
`gcry_malloc_secure' and `gcry_calloc_secure'. By calling `gcry_free'
on this memory, the memory and thus the keys are overwritten with zero
bytes before releasing the memory.
For use with the random number generator, Libgcrypt generates 3
internal keys which are stored in the encryption contexts used by the
RNG. These keys are stored in secure memory for the lifetime of the
process. Application are required to use `GCRYCTL_TERM_SECMEM' before
process termination. This will zero out the entire secure memory and
thus also the encryption contexts with these keys.

File: gcrypt.info, Node: Library Copying, Next: Copying, Prev: FIPS Mode, Up: Top
GNU Lesser General Public License
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END OF TERMS AND CONDITIONS
How to Apply These Terms to Your New Libraries
==============================================
If you develop a new library, and you want it to be of the greatest
possible use to the public, we recommend making it free software that
everyone can redistribute and change. You can do so by permitting
redistribution under these terms (or, alternatively, under the terms of
the ordinary General Public License).
To apply these terms, attach the following notices to the library.
It is safest to attach them to the start of each source file to most
effectively convey the exclusion of warranty; and each file should have
at least the "copyright" line and a pointer to where the full notice is
found.
ONE LINE TO GIVE THE LIBRARY'S NAME AND AN IDEA OF WHAT IT DOES.
Copyright (C) YEAR NAME OF AUTHOR
This library is free software; you can redistribute it and/or modify it
under the terms of the GNU Lesser General Public License as published by
the Free Software Foundation; either version 2.1 of the License, or (at
your option) any later version.
This library is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with this library; if not, write to the Free Software
Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307,
USA.
Also add information on how to contact you by electronic and paper
mail.
You should also get your employer (if you work as a programmer) or
your school, if any, to sign a "copyright disclaimer" for the library,
if necessary. Here is a sample; alter the names:
Yoyodyne, Inc., hereby disclaims all copyright interest in the library
`Frob' (a library for tweaking knobs) written by James Random Hacker.
SIGNATURE OF TY COON, 1 April 1990
Ty Coon, President of Vice
That's all there is to it!

File: gcrypt.info, Node: Copying, Next: Figures and Tables, Prev: Library Copying, Up: Top
GNU General Public License
**************************
Version 2, June 1991
Copyright (C) 1989, 1991 Free Software Foundation, Inc.
59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
Everyone is permitted to copy and distribute verbatim copies
of this license document, but changing it is not allowed.
Preamble
========
The licenses for most software are designed to take away your freedom
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under any particular circumstance, the balance of the section is
intended to apply and the section as a whole is intended to apply
in other circumstances.
It is not the purpose of this section to induce you to infringe any
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implemented by public license practices. Many people have made
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certain countries either by patents or by copyrighted interfaces,
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License may add an explicit geographical distribution limitation
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NO WARRANTY
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WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE
LAW. EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT
HOLDERS AND/OR OTHER PARTIES PROVIDE THE PROGRAM "AS IS" WITHOUT
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NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
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QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU. SHOULD THE
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WRITING WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY
MODIFY AND/OR REDISTRIBUTE THE PROGRAM AS PERMITTED ABOVE, BE
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INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF
DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU
OR THIRD PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY
OTHER PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN
ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.
END OF TERMS AND CONDITIONS
How to Apply These Terms to Your New Programs
=============================================
If you develop a new program, and you want it to be of the greatest
possible use to the public, the best way to achieve this is to make it
free software which everyone can redistribute and change under these
terms.
To do so, attach the following notices to the program. It is safest
to attach them to the start of each source file to most effectively
convey the exclusion of warranty; and each file should have at least
the "copyright" line and a pointer to where the full notice is found.
ONE LINE TO GIVE THE PROGRAM'S NAME AND AN IDEA OF WHAT IT DOES.
Copyright (C) 19YY NAME OF AUTHOR
This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License along
with this program; if not, write to the Free Software Foundation, Inc.,
59 Temple Place, Suite 330, Boston, MA 02111-1307, USA.
Also add information on how to contact you by electronic and paper
mail.
If the program is interactive, make it output a short notice like
this when it starts in an interactive mode:
Gnomovision version 69, Copyright (C) 19YY NAME OF AUTHOR
Gnomovision comes with ABSOLUTELY NO WARRANTY; for details
type `show w'. This is free software, and you are welcome
to redistribute it under certain conditions; type `show c'
for details.
The hypothetical commands `show w' and `show c' should show the
appropriate parts of the General Public License. Of course, the
commands you use may be called something other than `show w' and `show
c'; they could even be mouse-clicks or menu items--whatever suits your
program.
You should also get your employer (if you work as a programmer) or
your school, if any, to sign a "copyright disclaimer" for the program,
if necessary. Here is a sample; alter the names:
Yoyodyne, Inc., hereby disclaims all copyright
interest in the program `Gnomovision'
(which makes passes at compilers) written
by James Hacker.
SIGNATURE OF TY COON, 1 April 1989
Ty Coon, President of Vice
This General Public License does not permit incorporating your
program into proprietary programs. If your program is a subroutine
library, you may consider it more useful to permit linking proprietary
applications with the library. If this is what you want to do, use the
GNU Library General Public License instead of this License.

File: gcrypt.info, Node: Figures and Tables, Next: Concept Index, Prev: Copying, Up: Top
List of Figures and Tables
**************************
* Menu:
* Figure 16.1: Libgcrypt subsystems: fig:subsystems.
* Figure B.1: FIPS mode state ...: fig:fips-fsm.
* Menu:
* Table B.1: FIPS mode states: tbl:fips-states.
* Table B.2: FIPS mode state ...: tbl:fips-state-transitions.

File: gcrypt.info, Node: Concept Index, Next: Function and Data Index, Prev: Figures and Tables, Up: Top
Concept Index
*************
�[index�]
* Menu:
* 3DES: Available ciphers. (line 14)
* Advanced Encryption Standard: Available ciphers. (line 35)
* AES: Available ciphers. (line 35)
* AES-Wrap mode: Available cipher modes.
(line 32)
* Arcfour: Available ciphers. (line 52)
* Blowfish: Available ciphers. (line 22)
* bug emulation: Working with hash algorithms.
(line 36)
* Camellia: Available ciphers. (line 77)
* CAST5: Available ciphers. (line 19)
* CBC, Cipher Block Chaining mode: Available cipher modes.
(line 20)
* CBC-MAC: Working with cipher handles.
(line 55)
* CCM, Counter with CBC-MAC mode: Available cipher modes.
(line 45)
* CFB, Cipher Feedback mode: Available cipher modes.
(line 16)
* cipher text stealing: Working with cipher handles.
(line 48)
* comp: Cryptographic Functions.
(line 13)
* CRC32: Available hash algorithms.
(line 6)
* CTR, Counter mode: Available cipher modes.
(line 29)
* DES: Available ciphers. (line 57)
* DES-EDE: Available ciphers. (line 14)
* Digital Encryption Standard: Available ciphers. (line 14)
* ECB, Electronic Codebook mode: Available cipher modes.
(line 13)
* EdDSA: Cryptographic Functions.
(line 31)
* Enforced FIPS mode: Enabling FIPS mode. (line 30)
* error codes: Error Values. (line 6)
* error codes, list of <1>: Error Codes. (line 6)
* error codes, list of: Error Sources. (line 6)
* error codes, printing of: Error Strings. (line 6)
* error sources: Error Values. (line 6)
* error sources, printing of: Error Strings. (line 6)
* error strings: Error Strings. (line 6)
* error values: Error Values. (line 6)
* error values, printing of: Error Strings. (line 6)
* FIPS 140: Enabling FIPS mode. (line 6)
* FIPS 186 <1>: Public-Key Subsystem Architecture.
(line 51)
* FIPS 186: Cryptographic Functions.
(line 64)
* FIPS 186-2: Cryptographic Functions.
(line 72)
* FIPS mode: Enabling FIPS mode. (line 6)
* GCM, Galois/Counter Mode: Available cipher modes.
(line 50)
* GOST 28147-89: Available ciphers. (line 88)
* GPL, GNU General Public License: Copying. (line 6)
* hardware features: Hardware features. (line 6)
* HAVAL: Available hash algorithms.
(line 6)
* HMAC: Working with hash algorithms.
(line 27)
* HMAC-GOSTR-3411-94: Available MAC algorithms.
(line 6)
* HMAC-MD2, HMAC-MD4, HMAC-MD5: Available MAC algorithms.
(line 6)
* HMAC-RIPE-MD-160: Available MAC algorithms.
(line 6)
* HMAC-SHA-1: Available MAC algorithms.
(line 6)
* HMAC-SHA-224, HMAC-SHA-256, HMAC-SHA-384, HMAC-SHA-512: Available MAC algorithms.
(line 6)
* HMAC-Stribog-256, HMAC-Stribog-512: Available MAC algorithms.
(line 6)
* HMAC-TIGER1: Available MAC algorithms.
(line 6)
* HMAC-Whirlpool: Available MAC algorithms.
(line 6)
* IDEA: Available ciphers. (line 11)
* LGPL, GNU Lesser General Public License: Library Copying. (line 6)
* MD2, MD4, MD5: Available hash algorithms.
(line 6)
* no-blinding: Cryptographic Functions.
(line 39)
* nocomp: Cryptographic Functions.
(line 13)
* OAEP: Cryptographic Functions.
(line 25)
* OFB, Output Feedback mode: Available cipher modes.
(line 26)
* param: Cryptographic Functions.
(line 45)
* PKCS1: Cryptographic Functions.
(line 21)
* PSS: Cryptographic Functions.
(line 28)
* RC2: Available ciphers. (line 69)
* RC4: Available ciphers. (line 52)
* rfc-2268: Available ciphers. (line 69)
* RFC6979: Cryptographic Functions.
(line 36)
* Rijndael: Available ciphers. (line 35)
* RIPE-MD-160: Available hash algorithms.
(line 6)
* Salsa20: Available ciphers. (line 81)
* Salsa20/12: Available ciphers. (line 84)
* Seed (cipher): Available ciphers. (line 72)
* Serpent: Available ciphers. (line 65)
* SHA-1: Available hash algorithms.
(line 6)
* SHA-224, SHA-256, SHA-384, SHA-512: Available hash algorithms.
(line 6)
* sync mode (OpenPGP): Working with cipher handles.
(line 43)
* TIGER, TIGER1, TIGER2: Available hash algorithms.
(line 6)
* transient-key: Cryptographic Functions.
(line 50)
* Triple-DES: Available ciphers. (line 14)
* Twofish: Available ciphers. (line 46)
* Whirlpool: Available hash algorithms.
(line 6)
* X9.31 <1>: Public-Key Subsystem Architecture.
(line 51)
* X9.31: Cryptographic Functions.
(line 57)