Re: [TLS] More clarity on resumption and session hash

Nico Williams <nico@cryptonector.com> Wed, 27 May 2015 17:23 UTC

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Date: Wed, 27 May 2015 12:23:30 -0500
From: Nico Williams <nico@cryptonector.com>
To: Eric Rescorla <ekr@rtfm.com>
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Subject: Re: [TLS] More clarity on resumption and session hash
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On Mon, May 25, 2015 at 10:35:30AM -0700, Eric Rescorla wrote:
> This doesn't seem to distinguish between the two cases (original session
> did and did not use the extension), but they seem different, since the
> original session not using session hash is a common case (legacy) whereas
> an extension->no extension transition is an anomaly. Note that the client
> *is* required to send it, so I think there's a reasonably strong
> argument that the server should require it.
> 
> The two main options appear to be:
> 
>     1. Fall back to a full handshake.
>     2. Abort the connection
> 
> The argument for the first appears to be interop. The argument for the
> second appears to be that it's likely there is an error or a mid-flight
> reconfiguration on the client (which seems not good). My mild preference
> is for abort but I think it's important in any case that the draft be
> clear.

Is a mid-flight reconfiguration of the client while reusing an old
session cache likely?

Anyways, my preference would be to fallback, since I don't see the harm.
Correct me if I'm wrong.

Nico
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