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Re: [TLS] Call for consensus: Removing 0-RTT client auth

Benjamin Kaduk <bkaduk@akamai.com> Thu, 31 March 2016 17:08 UTC

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To: Bill Cox <waywardgeek@google.com>
References: <AABACDA8-6A12-4023-A971-1254CED4893F@sn3rd.com> <56FD154D.1030300@gmx.net> <CAH9QtQGBrvbPp4V8SMwK1WuUQpJKMo-1z8bs6rCO_d-w0JJE8A@mail.gmail.com>
From: Benjamin Kaduk <bkaduk@akamai.com>
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Date: Thu, 31 Mar 2016 12:08:08 -0500
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Cc: "<tls@ietf.org>" <tls@ietf.org>
Subject: Re: [TLS] Call for consensus: Removing 0-RTT client auth
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On 03/31/2016 12:02 PM, Bill Cox wrote:
> On Thu, Mar 31, 2016 at 5:17 AM, Hannes Tschofenig
> <hannes.tschofenig@gmx.net <mailto:hannes.tschofenig@gmx.net>> wrote:
>
>     Hi Sean,
>
>     we at ARM would find it somewhat unfortunate to remove the client
>     authentication feature from the 0-RTT exchange since this is one
>     of the
>     features that could speed up the exchange quite significantly and
>     would
>     make a big difference compared to TLS 1.2.
>
>
> Client certs can still be used with PSK 0-RTT, but only on the initial
> 1-RTT handshake.  it is up to the client to ensure that the security
> of the resumption master secret (RMS) is solid enough to warrant doing
> 0-RTT session resumption without re-verification of the client cert. 

That seems to rule out most corporate uses of client certs [for 0-RTT
client authentication], since I doubt anyone will be interested in
trusting that the client does so properly.

-Ben

> The simplest way to explain how the server should work in this case is
> to just say you need to emulate a session cache.
>

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