Subject: [eap] channel binding

From: Charles Clancy <[email-masked]>
Date: Mon, 29 Aug 2005 12:57:38 -0400 (EDT)

Channel binding transmits channel parameters between the EAP client and 
EAP server in some protected way.  When done by methods, it seems the 
general approach is to encrypt it (PSK, TTLS, etc), guaranteeing 
authenticity.  Is there any reason why it a MAC over the blob would be 
insufficient?  Is confidentiality required for some reason?

I'm working on defining a protected channel in EAP-PAX for communicating 
channel binding info, and I'd like to avoid defining a symmetric-key 
encryption ciphersuite, as PAX is based on MACs.

[ t. charles clancy ]--[ [email-masked] ]--[ www.cs.umd.edu/~clancy ]
[ computer science ]-----[ university of maryland | college park ]

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From: Yoshihiro Ohba <[email-masked]>
Date: Mon, 29 Aug 2005 14:05:58 -0400

> insufficient?  Is confidentiality required for some reason?

This is an interesting issue.  

I am not sure whether confidentiality is required for channel
parameters or not for existing lower layers.  But a solution that does
not necessarily require exposing channel parameters when exchanged
between peer and authenticator is certainly preferable, as I don't
think we can determine at this moment whether all lower layers
(including existing and future ones) do not require confidentiality.

Regarding carrying a MAC of a blob instead of a blob itself, I think
we need more analysis.  If a blob is mixture of confidential and
non-confidential parameters, can't the non-confidential parameters and
the MAC becomes a hint to find out the confidential ones?

Yoshihiro Ohba