Re: [TLS] draft-ietf-tls-cached-info-02 / New "Fast-Track" draft posted

Nikos Mavrogiannopoulos <nmav@gnutls.org> Tue, 02 February 2010 15:39 UTC

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Date: Tue, 02 Feb 2010 16:32:07 +0100
From: Nikos Mavrogiannopoulos <nmav@gnutls.org>
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Subject: Re: [TLS] draft-ietf-tls-cached-info-02 / New "Fast-Track" draft posted
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Adam Langley wrote:
[...]
> Given a client-speaks-first protocol like HTTP (which I happen to be
> mostly concerned with), this could cut the full handshake from two to
> one round trips.
> 
> However, there's a much easier way of doing this: cut through mode. In
> this scheme the client starts sending application data records without
> waiting for the server's Finished message so long as the ciphersuite
> is sufficiently strong. Android already does this.

What if I modify the server's messages, so you negotiate to a
ciphersuite I can break, or I can derive information from (say the
length of the plaintext data you send- as with rc4). You will not detect
my attack until you receive the server's finished message, wouldn't you?

I think this mode is walking on the edge.

regards,
Nikos