Re: [TLS] An SCSV to stop TLS fallback.

Adam Langley <agl@google.com> Tue, 26 November 2013 17:34 UTC

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From: Adam Langley <agl@google.com>
Date: Tue, 26 Nov 2013 12:34:32 -0500
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To: mrex@sap.com
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Subject: Re: [TLS] An SCSV to stop TLS fallback.
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On Mon, Nov 25, 2013 at 9:19 PM, Martin Rex <mrex@sap.com> wrote:
> If there is a problem in negotiating what _we_want_to_do_, because the
> installed base does not like the kind of negotiation that was originally
> proposed to be used, then the pragmatic engineering approach will be
> to define an alternative negotiation of at least a useful subset
> that will be compatible with the installed base, and which will not need
> to be stripped from a "conservative fallback handshake" -- and therefore
> will be resilient to downgrade attacks, and cope with retarded middle boxes.

Backporting AES-GCM, ECDHE, etc all the way back to SSLv3 is a
possibility if it comes to it. However, it's a lot more work than the
anti-fallback mechanisms currently under consideration so I'd want to
exclude them first.

I know know of a reason to believe that they would have less
compatibility problems than an SCSV.


Cheers

AGL