Re: [TLS] Wrapping up cached info

Nicolas Williams <Nicolas.Williams@oracle.com> Mon, 17 May 2010 14:58 UTC

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Date: Mon, 17 May 2010 09:57:38 -0500
From: Nicolas Williams <Nicolas.Williams@oracle.com>
To: Stefan Santesson <stefan@aaa-sec.com>
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References: <Pine.LNX.4.44.1005132018460.13071-100000@citation2.av8.net> <C8171810.ADE4%stefan@aaa-sec.com>
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Subject: Re: [TLS] Wrapping up cached info
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On Mon, May 17, 2010 at 03:58:08PM +0200, Stefan Santesson wrote:
> I don't think the discussion has shown that the security assumptions are
> wrong, I.e. That any alteration of cached data in the sense that the server
> and the client are in disagreement of what the cached data is, will lead to
> a handshake failure.

If only "any alteration of cached data" in that sense were to lead to
handshake failure, then the protocol would be secure.  The fact that
we've not shown as much means that the protocol is suspect.

We should not be concerned with DoS attacks here because DoS attacks on
handshakes can't be defended against by TLS.  We're concerned with all
other active attacks, and these matter a lot more than DoS attacks.

I believe the only obvious and simple way to prevent such attacks and,
crucially, simplify the security analysis of this protocol, is to bind
the cached objects' data into the handshake, almost as if they'd not
been cached in the first place.

Nico
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