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\page eap_peer_module EAP peer implementation
Extensible Authentication Protocol (EAP) is an authentication framework
defined in RFC 3748. %wpa_supplicant uses a separate code module for EAP
peer implementation. This module was designed to use only a minimal set
of direct function calls (mainly, to debug/event functions) in order for
it to be usable in other programs. The design of the EAP
implementation is based loosely on RFC 4137. The state machine is
defined in this RFC and so is the interface between the peer state
machine and methods. As such, this RFC provides useful information for
understanding the EAP peer implementation in %wpa_supplicant.
Some of the terminology used in EAP state machine is referring to
EAPOL (IEEE 802.1X), but there is no strict requirement on the lower
layer being IEEE 802.1X if EAP module is built for other programs than
%wpa_supplicant. These terms should be understood to refer to the
lower layer as defined in RFC 4137.
\section adding_eap_methods Adding EAP methods
Each EAP method is implemented as a separate module, usually as one C
file named eap_<name of the method>.c, e.g., eap_md5.c. All EAP
methods use the same interface between the peer state machine and
method specific functions. This allows new EAP methods to be added
without modifying the core EAP state machine implementation.
New EAP methods need to be registered by adding them into the build
(Makefile) and the EAP method registration list in the
eap_peer_register_methods() function of eap_methods.c. Each EAP
method should use a build-time configuration option, e.g., EAP_TLS, in
order to make it possible to select which of the methods are included
in the build.
EAP methods must implement the interface defined in eap_i.h. struct
eap_method defines the needed function pointers that each EAP method
must provide. In addition, the EAP type and name are registered using
this structure. This interface is based on section 4.4 of RFC 4137.
It is recommended that the EAP methods would use generic helper
functions, eap_msg_alloc() and eap_hdr_validate() when processing
messages. This allows code sharing and can avoid missing some of the
needed validation steps for received packets. In addition, these
functions make it easier to change between expanded and legacy EAP
header, if needed.
When adding an EAP method that uses a vendor specific EAP type
(Expanded Type as defined in RFC 3748, Chapter 5.7), the new method
must be registered by passing vendor id instead of EAP_VENDOR_IETF to
eap_peer_method_alloc(). These methods must not try to emulate
expanded types by registering a legacy EAP method for type 254. See
eap_vendor_test.c for an example of an EAP method implementation that
is implemented as an expanded type.
\section used_eap_library Using EAP implementation as a library
The Git repository has an eap_example directory that contains an
example showing how EAP peer and server code from %wpa_supplicant and
hostapd can be used as a library. The example program initializes both
an EAP server and an EAP peer entities and then runs through an
EAP-PEAP/MSCHAPv2 authentication.
eap_example_peer.c shows the initialization and glue code needed to
control the EAP peer implementation. eap_example_server.c does the
same for EAP server. eap_example.c is an example that ties in both the
EAP server and client parts to allow an EAP authentication to be
In this example, the EAP messages are passed between the server and
the peer are passed by direct function calls within the same process.
In practice, server and peer functionalities would likely reside in
separate devices and the EAP messages would be transmitted between the
devices based on an external protocol. For example, in IEEE 802.11
uses IEEE 802.1X EAPOL state machines to control the transmission of
EAP messages and WiMax supports optional PMK EAP authentication
mechanism that transmits EAP messages as defined in IEEE 802.16e.
The EAP library links in number of helper functions from src/utils and
src/crypto directories. Most of these are suitable as-is, but it may
be desirable to replace the debug output code in src/utils/wpa_debug.c
by dropping this file from the library and re-implementing the
functions there in a way that better fits in with the main