Re: [TLS] Don't Split HelloRetryRequest

Christopher Patton <cpatton@cloudflare.com> Thu, 01 April 2021 18:14 UTC

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From: Christopher Patton <cpatton@cloudflare.com>
Date: Thu, 1 Apr 2021 11:13:56 -0700
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To: Stephen Farrell <stephen.farrell@cs.tcd.ie>
Cc: Martin Thomson <mt@lowentropy.net>, "<tls@ietf.org>" <tls@ietf.org>
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Subject: Re: [TLS] Don't Split HelloRetryRequest
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> But let me ask a question meanwhile - how often does HRR
> actually happen and could we not just let ECH fail in a
> bunch of situations that would otherwise require all this
> new complexity?
>

One way HRR is used is in case the client's and server's cipher suite
preferences don't intersect. This feature is an essential part of TLS, as
there's no a priori reason why the client and server will initially
advertise overlapping preferences. (They usually do, hence the claim that
HRR is rare.) I don't think aborting the handshake instead of HRR is an
acceptable solution, as this would mean there are deployments with which
TLS couldn't be used.

Chris P.