802.1x and PEAP

From: Camillo Bucciarelli (camillobucciarelli_at_yahoo.it)
Date: 03/02/04

  • Next message: Giddens, Robert: "RE: help with exchange" 
    Date: Tue, 2 Mar 2004 11:15:55 +0100 (CET)
To: security-basics@securityfocus.com

    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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  • Next message: Giddens, Robert: "RE: help with exchange"

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