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Re: [TLS] Server Signature Algorithms

Nikos Mavrogiannopoulos <nmav@gnutls.org> Mon, 02 November 2009 19:10 UTC

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Sender: Nikos Mavrogiannopoulos <n.mavrogiannopoulos@gmail.com>
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Date: Mon, 02 Nov 2009 21:11:11 +0200
From: Nikos Mavrogiannopoulos <nmav@gnutls.org>
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To: Wan-Teh Chang <wtc@google.com>
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Cc: tls@ietf.org
Subject: Re: [TLS] Server Signature Algorithms
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Wan-Teh Chang wrote:

> Nikos: GnuTLS is one of the first TLS 1.2 implementations.
> How does GnuTLS deal with this issue now?  Does it compute
> hashes of all the hash algorithms it supports on the handshake
> messages, or does it buffer the handshake messages until
> the hash algorithm has been selected?

This part was only recently implemented. The current behavior is to not
buffer messages in order to keep common code base for all TLS versions
(none of the SSL, or TLS protocols so far required such buffering).
What we do is hash all the handshake messages with SHA-1 and SHA-256 and
hope that those will be among the choices of the server.

This works but it is a time bomb. Once one sets up a server that
requests some signature algorithm not in this set we do not complete
handshake.

regards,
Nikos

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