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Re: [TLS] checking on an scsv point

Martin Thomson <martin.thomson@gmail.com> Wed, 18 February 2015 00:55 UTC

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Date: Wed, 18 Feb 2015 11:55:07 +1100
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From: Martin Thomson <martin.thomson@gmail.com>
To: "mrex@sap.com" <mrex@sap.com>
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Subject: Re: [TLS] checking on an scsv point
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On 18 February 2015 at 11:48, Martin Rex <mrex@sap.com> wrote:
> But isn't that signal _already_ there: the request for the FALLBACK_SCSV.

Well, we were talking about the legacy case, where the request to
include the SCSV doesn't implicitly include permission to negotiate
version.max + 1.  TLS stacks that care about backward compatibility as
deeply as NSS does will want another signal to avoid the overload of
semantics.

> How does the App signal that the FALLBACK_SCSV should be included?

In the APIs I've seen (NSS + OpenSSL), the app configures the stack
with a reduced range of versions and they explicitly turn on the SCSV
with a separate option.

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