Re: [CHANNEL-BINDING] Updates to draft-altman-tls-channel-bindings (PLEASE REVIEW)

Nicolas Williams <Nicolas.Williams@sun.com> Fri, 19 March 2010 23:30 UTC

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Date: Fri, 19 Mar 2010 18:30:05 -0500
From: Nicolas Williams <Nicolas.Williams@sun.com>
To: Simon Josefsson <simon@josefsson.org>
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References: <20100317231522.GA18167@Sun.COM> <87zl243czl.fsf@mocca.josefsson.org>
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Cc: channel-binding@ietf.org, tls@ietf.org, sasl@ietf.org
Subject: Re: [CHANNEL-BINDING] Updates to draft-altman-tls-channel-bindings (PLEASE REVIEW)
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On Fri, Mar 19, 2010 at 09:57:34AM +0100, Simon Josefsson wrote:
> Nicolas Williams <Nicolas.Williams@sun.com> writes:
> 
> > +   Description: The first TLS Finished message sent (note: the Finished
> > +   struct) in the most recent TLS handshake of the TLS connection being
> > +   bound to (note: TLS connection, not session, so that the channel
> > +   binding is specific to each connection regardless of whether session
> > +   resumption is used).  If TLS re-negotiation takes place before the
> > +   channel binding operation, then the first TLS Finished message sent
> > +   of the latest/inner-most TLS connection is used.  Note that for full
> > +   TLS handshakes the first Finished message is sent by the client,
> > +   while for abbreviated TLS handshakes the first Finished message is
> > +   sent by the server.
> 
> I don't follow this fully -- IF you use the latest TLS finished message,
> the channel binding data WILL be specific the each TLS session, and it
> will depend on whether the session is resumed or not, which is contrary
> to this assertion:

No, the _first_ finished message of the _latest_ handshake.  That's what
Larry says MSFT implemented.  I still don't know if that's just for
HTTP/Negotiate or what.

> > +   bound to (note: TLS connection, not session, so that the channel
> > +   binding is specific to each connection regardless of whether session
> > +   resumption is used).  If TLS re-negotiation takes place before the
> 
> I wonder what happens if a TLS re-negotiation happens after the client
> started its authentication attempt (for GS2-KRB5: sent the AP-REQ) but
> before the server has responded (for GS2-KRB5: sent the AP-REP)?  Then
> authentication will fail, it seems, because the client and server will
> have different ideas of what the channel binding data should be.

Good question.  That's one reason to use the first handshake.