Re: [TLS] HelloRetryRequest question (was Re: TLS 1.3 Problem?)

Benjamin Kaduk <bkaduk@akamai.com> Wed, 30 September 2020 21:34 UTC

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Date: Wed, 30 Sep 2020 14:34:06 -0700
From: Benjamin Kaduk <bkaduk@akamai.com>
To: Michael D'Errico <mike-list@pobox.com>
Cc: tls@ietf.org
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Subject: Re: [TLS] HelloRetryRequest question (was Re: TLS 1.3 Problem?)
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On Wed, Sep 30, 2020 at 05:24:21PM -0400, Michael D'Errico wrote:
> I wrote:
> 
> > Also the server can't be actually stateless since
> > it needs to know the HelloRetryRequest message
> > for the transcript hash, right?
> 
> How can you even implement stateless HRR with a
> pseudo-session-ticket in the "cookie"?  The server
> needs to know the full HRR message to calculate the
> transcript hash, but this can't be part of the ticket
> since the ticket is included within the HRR, thus
> changing it....

The HRR is presumed to be a deterministic function of the
initial ClientHello, and as I discussed in my earlier message,
the server can reconstruct the initial ClientHello from the
second ClientHello and verify it against the hash in the cookie.

-Ben