Re: [TLS] Collisions (Re: Nico's suggestions - Re: Consensus Call:

Nicolas Williams <Nicolas.Williams@oracle.com> Tue, 11 May 2010 17:02 UTC

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Date: Tue, 11 May 2010 12:01:52 -0500
From: Nicolas Williams <Nicolas.Williams@oracle.com>
To: Martin Rex <mrex@sap.com>
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Cc: paul.hoffman@vpnc.org, tls@ietf.org
Subject: Re: [TLS] Collisions (Re: Nico's suggestions - Re: Consensus Call:
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On Tue, May 11, 2010 at 06:40:52PM +0200, Martin Rex wrote:
> Nicolas Williams wrote:
> > I don't see how to recover from collisions, transparently to apps,
> > without either adding round-trips, which is supposed to be a big no-no,
> > or making handshakes retriable (I'm assuming they aren't).
> 
> A theoretical possibility would be some kind of "epoch" counter by
> the server (or more general "peer", when caching is later extended
> to apply to client-side handshake data as well).  The server would
> have to bump that counter whenever it knows (or can not rule out)
> that the cachable data has changed.

That only helps when colliding objects all come from the same server.

> > > It normally requires closure of the existing connection and opening
> > > of a new connection because it is completely unspecified how to
> > > recover from a TLS handshake failure on a connection (and how to
> > > clear the network pipe from unprocessed data from the previous handshake).
> > 
> > It's easy to clear the "pipe" since the records have lengths.
> 
> There is *NO* guarantee that there are _only_ valid and complete TLS records
> left in the pipe.

Yeah, TLS handshakes are just not retriable.  You could have an
extension that makes them retriable, but if the TLS-GSS extension
foundered on state machine issues resulting from adding round-trips,
then so would an extension that makes handshakes retriable.

Nico
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