[TLS] Client attacks on stateless HRR? (was Re: Is stateless HelloRetryRequest worthwhile?)

Michael D'Errico <mike-list@pobox.com> Fri, 02 October 2020 18:47 UTC

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Date: Fri, 02 Oct 2020 14:46:55 -0400
From: "Michael D'Errico" <mike-list@pobox.com>
To: tls@ietf.org
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Archived-At: <https://mailarchive.ietf.org/arch/msg/tls/Ht6f2cvwGQHENaRDbupVgb8V-7g>
Subject: [TLS] =?utf-8?q?Client_attacks_on_stateless_HRR=3F_=28was_Re=3A_?= =?utf-8?q?_Is_stateless_HelloRetryRequest_worthwhile=3F=29?=
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> If the client is trying to perform 
> some sort of attack on the server by re-sending an old cookie, I assume 
> that a prerequisite for this attack is that the TLS handshake succeeds.

Maybe you don't need the handshake to succeed?  As a non-cryptographer
I can't say what the implications might be (as I said to Watson in private
email) but some of you are crypto people.  If you can create N parallel
sessions using the same cookie (send the same ClientHello1 with the
same Random value (?), or maybe trick a poorly-written server by sending
an initial ClientHello1 containing a cookie extension, or use DTLS (?)), what
could you do as a malicious client?  I don't know the answer, I'm asking.

Mike