eap Mailing List: RE: channel binding

[Salowey, Joe (jsalowey]

> -----Original Message-----
> From: Yoshihiro Ohba [mailto:yohba [at] tari.toshiba.com] 
> Sent: Monday, August 29, 2005 11:06 AM
> To: Charles Clancy
> Cc: eap [at] frascone.com
> Subject: Re: [eap] channel binding
> 
> On Mon, Aug 29, 2005 at 12:57:38PM -0400, Charles Clancy wrote:
> > 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?
> 
> 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?
> 
[Joe] Maybe, I don't think that a MAC necessarily has the properties of
a pseudo-random function so some information may leak into the MAC
value.  I'm not sure how close to a PRF something like HMAC is. 


> Yoshihiro Ohba
> 
> > 
> > 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 ]--[ tcc [at] umd.edu ]--[ 
> www.cs.umd.edu/~clancy ] [ 
> > computer science ]-----[ university of maryland | college park ]
> > 
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