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RE: 802.1x and PEAP
From: shankarnarayan.d () netsol co in
Date: Wed, 3 Mar 2004 11:45:24 +0530

The Lines below have been pulled straight from the PEAP working draft. This
clearly defines that the initial negotiation of the PEAP is as in the TLS -
thus providing the necessary security.
Hope this answers your question OR have I got it wrong - If you believe this
is not the information that you were looking for request you to please
rephrase your question

Shankar

Protected EAP (PEAP) Version 2 is comprised of a two-part
   conversation:

[1]  In Part 1, a TLS session is negotiated, with server authenticating
     to the client and optionally the client to the server.  The
     negotiated key is then used to encrypt the rest of the
     conversation.

[2]  In Part 2, within the TLS session, zero or more EAP methods are
     carried out.  Part 2 completes with a success/failure indication
     protected by the TLS session or a protected error (TLS alert).

The PEAP conversation typically begins with an optional identity
   exchange. The initial identity exchange is used primarily to route the
EAP
   conversation to the EAP server.  Since the initial identity exchange
   is in the clear, the peer MAY decide to place a routing realm instead
   of its real name in the EAP-Response/Identity.

In short, the first exchange is based on TLS where certificates are used
much in the same way as that used in the EAP-TLS. The remaining information
of identity etc is then pumped through the TLS tunnel. Hence, EAP-TLS may be
one of the methods (actually the most common method) used to establish the
tunnel (using certificates)

Shankar

-----Original Message-----
From: Camillo Bucciarelli [mailto:camillobucciarelli () yahoo it] 
Sent: Tuesday, March 02, 2004 3:46 PM
To: security-basics () securityfocus com
Subject: 802.1x and PEAP

Good morning,
  I'm looking for detailed information about the
Protected EAP. I can't understand what the supplicant
and Access Server use to establish the TLS tunnel.
Here's an example:
 
Authenticating Peer     Authenticator
-------------------     -------------
                        <- EAP-Request/
                        Identity
EAP-Response/
Identity (MyID) ->
                        <- EAP-Request/
                        EAP-Type=PEAP, V=0
                        (PEAP Start, S bit set)
 
EAP-Response/
EAP-Type=PEAP, V=0
(TLS client_hello)->
                        <- EAP-Request/
                        EAP-Type=PEAP, V=0
                        (TLS server_hello,
                         TLS certificate,
                 [TLS server_key_exchange,]
                 [TLS certificate_request,]
                     TLS server_hello_done)
EAP-Response/
EAP-Type=PEAP, V=0
([TLS certificate,]
 TLS client_key_exchange,
[TLS certificate_verify,]
 TLS change_cipher_spec,
 TLS finished) ->
                        <- EAP-Request/
                        EAP-Type=PEAP, V=0
                        (TLS change_cipher_spec,
                         TLS finished)
EAP-Response/
EAP-Type=PEAP ->
 
TLS channel established
(messages sent within the TLS channel)
 
They exchange a server_key_exchange and a
client_key_exchange used to derive the session key. 


It seems to me that the key exchange between the
client and the server is done in clear text, but this
means that I can actually sniff this exchange. Now,
this seems not logical to me.  Anyone here has any
idea about "where" I am wrong ? Do the two elements
hash in some way the keys ?  Or, another possibility,
do we actually have the client key encrypted with the
public key that belongs to the server - that is of
course available - and we have the server key *only*
that is transmitted in clear text ?  In the TLS
protocol of course the two key are encrypted with the
ublic key of the "other end".  But in PEAP ?

Thanks in advance,
Camillo

=====
Camillo Bucciarelli
 



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