doc/HACKING - nest-hello/510950009/libgcrypt - Git at Google

 # HACKING                                                       -*- org -*-
 #+TITLE: Hacking notes for Libgcrypt
 #+STARTUP: showall

 * How to contribute

   The following stuff explains some basic procedures you need to
   follow if you want to contribute code or documentation.

 ** No more ChangeLog files

   Do not modify any of the ChangeLog files in Libgcrypt.  Starting on
   December 1st, 2011 we put change information only in the GIT commit
   log, and generate a top-level ChangeLog file from logs at "make
   dist" time.  As such, there are strict requirements on the form of
   the commit log messages.  The old ChangeLog files have all be
   renamed to ChangeLog-2011

 ** Commit log requirements

   Your commit log should always start with a one-line summary, the
   second line should be blank, and the remaining lines are usually
   ChangeLog-style entries for all affected files.  However, it's fine
   -- even recommended -- to write a few lines of prose describing the
   change, when the summary and ChangeLog entries don't give enough of
   the big picture.  Omit the leading TABs that you're used to seeing
   in a "real" ChangeLog file, but keep the maximum line length at 72
   or smaller, so that the generated ChangeLog lines, each with its
   leading TAB, will not exceed 80 columns.

 ** License policy

   Libgcrypt is currently licensed under the LGPLv2+ with tools and the
   manual being under the GPLv2+.  We may eventually update to a newer
   version of the licenses or a combination of them.  It is thus
   important, that all contributed code allows for an update of the
   license; for example we can't accept code under the LGPLv2(only).

   Libgcrypt used to have a strict policy of requiring copyright
   assignments to the FSF.  To avoid this major organizational overhead
   and to allow inclusion of code, not copyrighted by the FSF, this
   policy has been relaxed.  It is now also possible to contribute code
   by asserting that the contribution is in accordance to the
   "Libgcrypt Developer's Certificate of Origin" as found in the file
   "DCO".  (Except for a slight wording change, this DCO is identical
   to the one used by the Linux kernel.)

   If your want to contribute code or documentation to Libgcrypt and
   you didn't signed a copyright assignment with the FSF in the past,
   you need to take these simple steps:

   - Decide which mail address you want to use.  Please have your real
     name in the address and not a pseudonym.  Anonymous contributions
     can only be done if you find a proxy who certifies for you.

   - If your employer or school might claim ownership of code written
     by you; you need to talk to them to make sure that you have the
     right to contribute under the DCO.

   - Send an OpenPGP signed mail to the gcrypt-devel@gnupg.org mailing
     list from your mail address.  Include a copy of the DCO as found
     in the official master branch.  Insert your name and email address
     into the DCO in the same way you want to use it later.  Example:

       Signed-off-by: Joe R. Hacker <joe@example.org>

     (If you really need it, you may perform simple transformations of
     the mail address: Replacing "@" by " at " or "." by " dot ".)

   - That's it.  From now on you only need to add a "Signed-off-by:"
     line with your name and mail address to the commit message.  It is
     recommended to send the patches using a PGP/MIME signed mail.

 ** Coding standards

   Please follow the GNU coding standards.  If you are in doubt consult
   the existing code as an example.  Do no re-indent code without a
   need.  If you really need to do it, use a separate commit for such a
   change.


 * Porting hints
 ** Taking optimized MPI code out of GMP:

   I generated the pentium4/* files by glueing the existing assembler
   prologues to the GMP 4.2.1 assembler files generated with the m4
   tool in GMP's build process, for example:

     $ m4 -DHAVE_CONFIG_H -D__GMP_WITHIN_GMP -DOPERATION_rshift -DPIC \
       rshift.asm >tmp-rshift.s

   Then tmp-rshift will contain the assembler instructions for the
   configured platform.  Unfortunately, this way the comments are lost.
   For most files I re-inserted some of the comments, but this is
   tedious work.


 * Debug hints

 ** Debugging math stuff:

   While debugging the ECC code in libgcrypt, I was in need for some
   computer algebra system which would allow me to verify the numbers
   in the debugging easily.  I found that PARI (pari-gp package in
   Debian) has support for elliptic curves.  The below commands shows
   how they are set up and used with an example.

   ===8<========
   hextodec(s)=local(v=Vec(s),a=10,b=11,c=12,d=13,e=14,f=15,A=10,B=11,C=12,D=13,E=14,F=15,h);if(#setunion(Set(v),Vec("0123456789ABCDEFabcdef"))>22,error);for(i=1,#v,h=shift(h,4)+eval(v[i]));h

   p = hextodec("01FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF")
   a = hextodec("01FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFC")
   b = hextodec("51953EB9618E1C9A1F929A21A0B68540EEA2DA725B99B315F3B8B489918EF109E156193951EC7E937B1652C0BD3BB1BF073573DF883D2C34F1EF451FD46B503F00")

   /* Set up y^2 = x^3 + ax + b mod (p).  */
   e = ellinit(Mod(1,p)*[0,0,0,a,b]);

   gx = hextodec ("00C6858E06B70404E9CD9E3ECB662395B4429C648139053FB521F828AF606B4D3DBAA14B5E77EFE75928FE1DC127A2FFA8DE3348B3C1856A429BF97E7E31C2E5BD66")
   gy = hextodec ("011839296A789A3BC0045C8A5FB42C7D1BD998F54449579B446817AFBD17273E662C97EE72995EF42640C550B9013FAD0761353C7086A272C24088BE94769FD16650")
   g = Mod(1,p)*[gx,gy]

   n = hextodec ("01FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFA51868783BF2F966B7FCC0148F709A5D03BB5C9B8899C47AEBB6FB71E91386409")

   /* Verify that G is on the curve, and that n is the order.  */
   ellisoncurve (e,g)
   isprime (n)
   ellpow (e,g,n)

   d = hextodec ("018F9573F25059571BDF614529953DE2540497CEDABD04F3AF78813BED7BB163A2FD919EECF822848FCA39EF55E500F8CE861C7D53D371857F7774B79428E887F81B")

   qx = hextodec ("00316AAAD3E905875938F588BD9E8A4785EF9BDB76D62A83A5340F82CB8E800B25619F5C3EA02B7A4FA43D7497C7702F7DFBEAC8E8F92C3CAABD9F84182FDA391B3B")
   /* Note: WRONG! (It is apparent that this is the same as X shifted by
      8 bit).  */
   qy = hextodec ("0000316AAAD3E905875938F588BD9E8A4785EF9BDB76D62A83A5340F82CB8E800B25619F5C3EA02B7A4FA43D7497C7702F7DFBEAC8E8F92C3CAABD9F84182FDA391B")
   q = Mod(1,p)*[qx,qy]

   /* Calculate what Q should be given d.  */
   ellpow (e,g,d)

   /* This is not 0 and thus shows that libgcrypt gave Q and d that do
   not match.  */
   ellpow (e,g,d) - q
   ====8<=====================
	# HACKING -- org --
	#+TITLE: Hacking notes for Libgcrypt
	#+STARTUP: showall

	* How to contribute

	The following stuff explains some basic procedures you need to
	follow if you want to contribute code or documentation.

	** No more ChangeLog files

	Do not modify any of the ChangeLog files in Libgcrypt. Starting on
	December 1st, 2011 we put change information only in the GIT commit
	log, and generate a top-level ChangeLog file from logs at "make
	dist" time. As such, there are strict requirements on the form of
	the commit log messages. The old ChangeLog files have all be
	renamed to ChangeLog-2011

	** Commit log requirements

	Your commit log should always start with a one-line summary, the
	second line should be blank, and the remaining lines are usually
	ChangeLog-style entries for all affected files. However, it's fine
	-- even recommended -- to write a few lines of prose describing the
	change, when the summary and ChangeLog entries don't give enough of
	the big picture. Omit the leading TABs that you're used to seeing
	in a "real" ChangeLog file, but keep the maximum line length at 72
	or smaller, so that the generated ChangeLog lines, each with its
	leading TAB, will not exceed 80 columns.

	** License policy

	Libgcrypt is currently licensed under the LGPLv2+ with tools and the
	manual being under the GPLv2+. We may eventually update to a newer
	version of the licenses or a combination of them. It is thus
	important, that all contributed code allows for an update of the
	license; for example we can't accept code under the LGPLv2(only).

	Libgcrypt used to have a strict policy of requiring copyright
	assignments to the FSF. To avoid this major organizational overhead
	and to allow inclusion of code, not copyrighted by the FSF, this
	policy has been relaxed. It is now also possible to contribute code
	by asserting that the contribution is in accordance to the
	"Libgcrypt Developer's Certificate of Origin" as found in the file
	"DCO". (Except for a slight wording change, this DCO is identical
	to the one used by the Linux kernel.)

	If your want to contribute code or documentation to Libgcrypt and
	you didn't signed a copyright assignment with the FSF in the past,
	you need to take these simple steps:

	- Decide which mail address you want to use. Please have your real
	name in the address and not a pseudonym. Anonymous contributions
	can only be done if you find a proxy who certifies for you.

	- If your employer or school might claim ownership of code written
	by you; you need to talk to them to make sure that you have the
	right to contribute under the DCO.

	- Send an OpenPGP signed mail to the gcrypt-devel@gnupg.org mailing
	list from your mail address. Include a copy of the DCO as found
	in the official master branch. Insert your name and email address
	into the DCO in the same way you want to use it later. Example:

	Signed-off-by: Joe R. Hacker <joe@example.org>

	(If you really need it, you may perform simple transformations of
	the mail address: Replacing "@" by " at " or "." by " dot ".)

	- That's it. From now on you only need to add a "Signed-off-by:"
	line with your name and mail address to the commit message. It is
	recommended to send the patches using a PGP/MIME signed mail.

	** Coding standards

	Please follow the GNU coding standards. If you are in doubt consult
	the existing code as an example. Do no re-indent code without a
	need. If you really need to do it, use a separate commit for such a
	change.


	* Porting hints
	** Taking optimized MPI code out of GMP:

	I generated the pentium4/* files by glueing the existing assembler
	prologues to the GMP 4.2.1 assembler files generated with the m4
	tool in GMP's build process, for example:

	$ m4 -DHAVE_CONFIG_H -D__GMP_WITHIN_GMP -DOPERATION_rshift -DPIC \
	rshift.asm >tmp-rshift.s

	Then tmp-rshift will contain the assembler instructions for the
	configured platform. Unfortunately, this way the comments are lost.
	For most files I re-inserted some of the comments, but this is
	tedious work.


	* Debug hints

	** Debugging math stuff:

	While debugging the ECC code in libgcrypt, I was in need for some
	computer algebra system which would allow me to verify the numbers
	in the debugging easily. I found that PARI (pari-gp package in
	Debian) has support for elliptic curves. The below commands shows
	how they are set up and used with an example.

	===8<========
	hextodec(s)=local(v=Vec(s),a=10,b=11,c=12,d=13,e=14,f=15,A=10,B=11,C=12,D=13,E=14,F=15,h);if(#setunion(Set(v),Vec("0123456789ABCDEFabcdef"))>22,error);for(i=1,#v,h=shift(h,4)+eval(v[i]));h

	p = hextodec("01FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF")
	a = hextodec("01FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFC")
	b = hextodec("51953EB9618E1C9A1F929A21A0B68540EEA2DA725B99B315F3B8B489918EF109E156193951EC7E937B1652C0BD3BB1BF073573DF883D2C34F1EF451FD46B503F00")

	/* Set up y^2 = x^3 + ax + b mod (p). */
	e = ellinit(Mod(1,p)*[0,0,0,a,b]);

	gx = hextodec ("00C6858E06B70404E9CD9E3ECB662395B4429C648139053FB521F828AF606B4D3DBAA14B5E77EFE75928FE1DC127A2FFA8DE3348B3C1856A429BF97E7E31C2E5BD66")
	gy = hextodec ("011839296A789A3BC0045C8A5FB42C7D1BD998F54449579B446817AFBD17273E662C97EE72995EF42640C550B9013FAD0761353C7086A272C24088BE94769FD16650")
	g = Mod(1,p)*[gx,gy]

	n = hextodec ("01FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFA51868783BF2F966B7FCC0148F709A5D03BB5C9B8899C47AEBB6FB71E91386409")

	/* Verify that G is on the curve, and that n is the order. */
	ellisoncurve (e,g)
	isprime (n)
	ellpow (e,g,n)

	d = hextodec ("018F9573F25059571BDF614529953DE2540497CEDABD04F3AF78813BED7BB163A2FD919EECF822848FCA39EF55E500F8CE861C7D53D371857F7774B79428E887F81B")

	qx = hextodec ("00316AAAD3E905875938F588BD9E8A4785EF9BDB76D62A83A5340F82CB8E800B25619F5C3EA02B7A4FA43D7497C7702F7DFBEAC8E8F92C3CAABD9F84182FDA391B3B")
	/* Note: WRONG! (It is apparent that this is the same as X shifted by
	8 bit). */
	qy = hextodec ("0000316AAAD3E905875938F588BD9E8A4785EF9BDB76D62A83A5340F82CB8E800B25619F5C3EA02B7A4FA43D7497C7702F7DFBEAC8E8F92C3CAABD9F84182FDA391B")
	q = Mod(1,p)*[qx,qy]

	/* Calculate what Q should be given d. */
	ellpow (e,g,d)

	/* This is not 0 and thus shows that libgcrypt gave Q and d that do
	not match. */
	ellpow (e,g,d) - q
	====8<=====================