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

Adam Langley <agl@google.com> Tue, 26 November 2013 17:39 UTC

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From: Adam Langley <agl@google.com>
Date: Tue, 26 Nov 2013 12:38:47 -0500
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To: Trevor Perrin <trevp@trevp.net>
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Subject: Re: [TLS] An SCSV to stop TLS fallback.
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On Mon, Nov 25, 2013 at 9:33 PM, Trevor Perrin <trevp@trevp.net> wrote:
> Are these MITM products using special root certs installed in the
> browser for MITM purposes?

Yes.

> If so, could the browser simply allow
> SSLv3 fallback only when connecting to a cert under such an installed
> root, while otherwise rejecting such a fallback?

Yes, but I don't believe that would be viable on the Internet as a
whole. There are certainly many HTTPS servers on the Internet that
need fallback in order to function. We would like not to break them
while stopping them dragging everyone's security down. So we still
need some way to identify non-broken servers. At the moment we're
doing that with an "if (is_google)", but that's just an experiment. We
would need an SCSV or the existing renego signal to deploy this
properly in any case, although a root check would fix the current
experiment.


Cheers

AGL