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802.1x and PEAP
From: Camillo Bucciarelli <camillobucciarelli () yahoo it>
Date: Tue, 2 Mar 2004 11:15:55 +0100 (CET)

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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