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==Extensible Authentication Protocol (EAP)==


===INTRODUCTION===

Extensible Authentication Protocol(EAP), RFC 2284, is a general protocol that allows network access points to support multiple authentication methods. Each EAP-Type indicates a specific authentication mechanism.  802.1x standard authenticates wireless LAN users trying to access enterprise networks.

RADIUS attribute used for EAP is EAP-Message, 79(RFC 2869). RADIUS communicates all EAP messages by embedding them in this attribute.

====General Terminology====
; Supplicant/EAP Client
: the software on the end-user/client machine (machine with the wireless card).

; Authenticator/NAS/Access Point(AP)
: A network device providing users with a point of entry into the network.

; EAPOL
: EAP over LAN as defined in 802.1x standard.

; EAPOW
: EAP over Wireless.

   +----------+        +----------+        +----------+
   |          |  EAPOL |          | RADIUS |          |
   |  EAP     |<------>|  Access  |<------>|  RADIUS  |
   |  Client  |  EAPOW |  Point   |  (EAP) |  Server  |
   |          |        |          |        |          |
   +----------+        +----------+        +----------+

The sequence of events, for EAP-MD5, runs as follows:
# The end-user associates with the Access Point(AP).
# The supplicant specifies AP to use EAP by sending EAP-Start.
# AP requests the supplicant to Identify itself (EAP-Identity).
# Supplicant then sends its Identity (username) to the AP.
# AP forwards this EAP-response AS-IS to the RADIUS server.  (The supplicant and the RADIUS server mutually authenticate via AP.  AP just acts as a passthru till authentication is finished.)
# The server sends a challenge to the supplicant.
# The supplicant carries out a hash on the password and sends this hashed password to the RADIUS server as its response.
# The RADIUS server performs a hash on the password for that supplicant in its user database and compares the two hashed values and authenticates the client if the two values match(EAP-Success/EAP-Failure)
# AP now opens a port to accept data from the end-user.

Currently, EAP is widely used in wireless networks than in wired networks.  In 802.11/wireless based networking, following sequence of events happen in addition to the above EAP events.

# RADIUS server and the supplicant agree to a specific WEP key.
# The supplicant loads the key ready for logging on.
# The RADIUS server sends the key for this session (Session key) to the AP.
# The AP encrypts its Broadcast key with the Session key
# The AP sends the encypted key to the supplicant
# The supplicant decrypts the Broadcast key with the Session key and the session continues using the Broadcast and Session keys until the session ends.

===References===
The Implementation of EAP over RADIUS is based on the following RFCs
* RFC 2869 -- RADIUS Extensions
* RFC 2284 -- PPP Extensible Authentication Protocol (EAP)
* RFC 2716 -- PPP EAP TLS Authentication Protocol

Following links help to understand HOW EAP works
* http://www.ieee802.org/1/files/public/docs2000/ieee_plenary.PDF

===EAP CODE ORGANIZATION===

EAP is implemented as a module in freeradius and the code is placed in src/modules/rlm_eap.  All EAP-Types are organized as subdirectories in rlm_eap/types/.  Currently Freeradius supports only 2 EAP-Types (EAP-MD5, EAP-TLS).

Each EAP-Type, like types/rlm_eap_md5, contains a chunk of code that knows how to deal with a particular kind of authentication mechanism.

To add a new EAP-Type then a new directory should be created as rlm_eap/types/rlm_eap_XXXX, where XXXX is EAP-Type name ie for EAP-Type like ONE TIME PASSWORD (OTP) it would be rlm_eap_otp

{| class="wikitable"
| src/modules/rlm_eap
| contains the basic EAP and generalized interfaces to all the EAP-Types.
|-
| rlm_eap/types
| contains all the supported EAP-Types
|-
| rlm_eap/types/rlm_eap_md5
| EAP-MD5 authentication.
|-
| rlm_eap/types/rlm_eap_tls
| EAP-TLS based authentication.
|-
| rlm_eap/types/rlm_eap_leap
| Cisco LEAP authentication.
|-
| rlm_eap/types/rlm_eap_sim
| EAP-SIM (GSM) based authentication
|-
|}

===CONFIGURATION===
Add the eap configuration stanza to the modules section in [[radiusd.conf]] to load and control rlm_eap and all the supported EAP-Types:

For example:
 modules {
 		...
 		eap {
 			default_eap_type = md5
 
 			md5 {
 			}
 		    ...
 		}
 		...
 	}

NOTE: You cannot have empty eap stanza. At least one EAP-Type sub-stanza  should be defined as above, otherwise the server will not know what type of eap authentication mechanism to be used and the server will exit with error.

All the various options and their associated default values for each EAP-Type are documented in the sample radiusd.conf that is provided with the distribution.

Since the EAP requests may not contain a requested EAP type, the 'default_eap_type' configuration options is used by the EAP module to determine which EAP type to choose for authentication.

NOTE: EAP cannot authorize a user. It can only authenticate. Other Freeradius modules authorize the user and lets EAP to authenticate.

NOTE: There can only be one instance of the EAP module.

See the [[eap.conf]] as included in FreeRADIUS.

===EAP SIM server===

To configure EAP-SIM authentication, the following attributes must be set in the server. This can be done in the users file, but in many cases will be taken from a database server, via one of the SQL interface.

If one has SIM cards that one controls (i.e. whose share secret you know),   one should be able to write a module to generate these attributes (the triplets) in the server. 

If one has access to the SS7 based settlement network, then a module to fetch appropriate triplets could be written. This module would act as an authorization only module.

The attributes are:
 	EAP-Sim-Rand1 		16 bytes
 	EAP-Sim-SRES1 		 4 bytes
 	EAP-Sim-KC1 		 8 bytes
 	EAP-Sim-Rand2 		16 bytes
 	EAP-Sim-SRES2 		 4 bytes
 	EAP-Sim-KC2 		 8 bytes
 	EAP-Sim-Rand3 		16 bytes
 	EAP-Sim-SRES3 		 4 bytes
 	EAP-Sim-KC3 		 8 bytes

EAP-SIM will send WEP attributes to the resquestor.

===EAP CLIENTS===

See [[EAP Clients]]

===TESTING===

You will find several test cases in src/tests/ for the EAP-SIM code.

{{Default in the server source|src/tests/}}

===HOW DO I USE IT (FAQ/Examples)===

==== How can I enable EAP-MD5 authentication? ====

In the module configuration (radiusd.conf or modules/eap)

        modules {
                ...
                eap {
                        default_eap_type = md5
                        md5 {
                        }
                        ...
                }
                ...
        }

In the server configuration (radiusd.conf or sites-available/default)

        # eap sets the authenticate type as EAP
        authorize {
                ...
                eap
        }

        # eap authentication takes place.
        authenticate {
                eap
        }

        # If you are proxying EAP-LEAP requests
        # This is required to make LEAP work.
        post-proxy {
                eap
        }

==== My Userbase is in LDAP and I want to use EAP-MD5 authentication ====

In the module configuration (radiusd.conf or modules/eap)

        modules {
                ...
                eap {
                        default_eap_type = md5
                        md5 {
                        }
                        ...
                }
                ...
        }
 
In the server configuration (radiusd.conf or sites-available/default)

        # ldap gets the Configured password.
        # eap sets the authenticate type as EAP
        authorize {
                ldap
                eap
        }

        # eap authentication takes place.
        authenticate {
                eap
        }

==== How can I Proxy EAP messages, with/without User-Name attribute in the Access-Request packets ====

With User-Name attribute in Access-Request packet,
EAP-proxying is just same as RADIUS-proxying.

If User-Name attribute is not present in Access-Request packet,
Freeradius can proxy the request with the following 
in the server configuration (radiusd.conf or sites-available/default):

   # eap module should be configured as the First module in 
   # the authorize stanza

        authorize {
                eap
                ...  other modules.
        }

With this configuration, eap_authorize creates User-Name attribute
from EAP-Identity response, if it is not present.
Once User-Name attribute is created, RADIUS proxying takes care
of EAP proxying.

==== How Freeradius can handle EAP-START messages? ====

In most of the cases this is handled by the Authenticator.

Only if it is required then, in the server configuration
(radiusd.conf or sites-available/default)

        authorize {
                eap
                ...  other modules.
        }

With the above configuration, RADIUS server immediately responds with
EAP-Identity request.
	
NOTE: EAP doesnot check for any Identity or maintains any state in case
of EAP-START. It blindly responds with EAP-Identity request.
Proxying is handled only after EAP-Identity response is received.

==== I want to enable multiple EAP-Types, how can I configure? ====
  
In the module configuration (radiusd.conf or modules/eap)

        modules {
                ...
                eap {
                        default_eap_type = tls
                        md5 {
                        }
                        tls {
                                ...
                        }
                        ...
                }
                ...
        }

The above configuration will let the server load all the EAP-Types,
but the server can have only one default EAP-Type, as above.

Once EAP-Identity response is received by the server, based on the
default_eap_type, the server will send a new request (MD5-Challenge 
request incase of md5, TLS-START request incase of tls) to the supplicant.
If the supplicant is RFC 2284 compliant and doesnot support the
EAP-Type sent by the server then it sends EAP-Acknowledge with the
supported EAP-Type. If this EAP-Type is supported by the server then it 
will send the respective EAP-request.
  
Example: If the supplicant supports only EAP-MD5 but the server
default_eap_type is configured as EAP-TLS, as above, then the server
will send TLS-START after EAP-Identity is received. Supplicant will
respond with EAP-Acknowledge(EAP-MD5). Server now responds with
MD5-Challenge.

===INSTALLATION===
EAP, EAP-MD5, and Cisco LEAP do not require any additional packages.  [[FreeRADIUS]] contains all the required packages.

For EAP-TLS, [http://www.openssl.org/ OPENSSL] is required to be installed.  Any version from 0.9.7, should fairly work with this module.

EAP-SIM should not require any additional packages.

===CAVEATS===
It probably still has bugs.  Most notably, there is a small memory leak somewhere in the eap_tls code.  I suspect it's because of my misuse of OPENSSL libraries, but I have no proof yet.

===IMPLEMENTATION (For Developers)===

The rlm_eap module only deals with EAP specific authentication mechanism and the generic interface to interact with all the EAP-Types.

Currently, these are the existing interfaces,
        int        attach(CONF_SECTION *conf, void **type_arg);
        int        initiate(void *type_arg, EAP_HANDLER *handler);
        int        authenticate(void *type_arg, EAP_HANDLER *handler);
        int        detach(void **type_arg);

attach() and detach() functions allocate and deallocate all the required resources.

initiate() function begins the conversation when EAP-Identity response is received. Incase of EAP-MD5, initiate() function sends the challenge.

authenticate() function uses specific EAP-Type authentication mechanism to authenticate the user. During authentication many EAP-Requests and EAP-Responses takes place for each authentication. Hence authenticate() function may be called many times. EAP_HANDLER contains the complete state information required.

===HOW EAP WORKS===
as posted to the list, by John Lindsay <jlindsay@internode.com.au>

To make it clear for everyone, the supplicant is the software on the client (machine with the wireless card).

The EAP process doesn't start until the client has associated with the Access Point using Open authentication.  If this process isn't crystal clear you need to go away and gain understanding.

Once the association is made the AP blocks all traffic that is not 802.1x so although associated the connection only has value for EAP.  Any EAP traffic is passed to the radius server and any radius traffic is passed back to the client.

So, after the client has associated to the Access Point, the supplicant starts the process for using EAP over LAN by asking the user for their logon and password.

Using 802.1x and EAP the supplicant sends the username and a one-way hash of the password to the AP.

The AP encapsulates the request and sends it to the RADIUS server.

The radius server needs a plaintext password so that it can perform the same one-way hash to determine that the password is correct.  If it is, the radius server issues an access challenge which goes back via to the AP to the client. (my study guide says client but my brain says 'supplicant')

The client sends the EAP response to the challenge via the AP to the RADIUS server.

If the response is valid the RADIUS server sends a success message and the session WEP key (EAP over wireless) to the client via the AP.  The same session WEP key is also sent to the AP in the success packet.

The client and the AP then begin using session WEP keys. The WEP key used for multicasts is then sent from the AP to the client.  It is encrypted using the session WEP key.

===ACKNOWLEDGEMENTS===
Primary author - Raghu <raghud@mail.com>

EAP-SIM	 - Michael Richardson <mcr@sandelman.ottawa.on.ca>

The development of the EAP/SIM support was funded by [http://www.nic.at/ipa Internet Foundation Austria].

==See also==
* [[EAP module changes]]
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