Re: [TLS] Cipher suite values to indicate TLS capability

Geoffrey Keating <geoffk@geoffk.org> Wed, 06 June 2012 00:06 UTC

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To: Adam Langley <agl@google.com>
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From: Geoffrey Keating <geoffk@geoffk.org>
Date: Tue, 05 Jun 2012 17:06:56 -0700
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Cc: tls@ietf.org
Subject: Re: [TLS] Cipher suite values to indicate TLS capability
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Adam Langley <agl@google.com> writes:

> On Tue, Jun 5, 2012 at 7:41 PM, Geoffrey Keating <geoffk@geoffk.org> wrote:
> > Why would you need to send the extensions?  (The RFC says they're
> > optional.)
> 
> Well, we could cross our fingers and hope that the server picks
> something acceptable I guess (or simply define the set of acceptable
> values for SSLv3). But extending SSLv3 to support ECDHE seems rather
> specific:

I think I'll go out on a limb and say that there are not any
SSLv3-only servers which actually support ECDHE, so if you fall back
to SSLv3 and yet ECDHE gets picked, you're under a downgrade attack
and the appropriate thing is to close that connection (and fall back
up, or whatever).  It doesn't matter what the server picks for the
parameters, you'd never want to use them.

Likewise there are probably not any SSLv3-only clients which support
ECDHE, so if you're a server and you get such a request, you can
probably close that connection too.

Re: [TLS] Cipher suite values to indicate TLS cap… Geoffrey Keating
[TLS] Cipher suite values to indicate TLS capabil… Adam Langley
Re: [TLS] Cipher suite values to indicate TLS cap… Adam Langley
Re: [TLS] Cipher suite values to indicate TLS cap… Geoffrey Keating
Re: [TLS] Cipher suite values to indicate TLS cap… Adam Langley
Re: [TLS] Cipher suite values to indicate TLS cap… Adam Langley
Re: [TLS] Cipher suite values to indicate TLS cap… Geoffrey Keating
Re: [TLS] Cipher suite values to indicate TLS cap… Adam Langley
Re: [TLS] Cipher suite values to indicate TLS cap… Chris Richardson
Re: [TLS] Cipher suite values to indicate TLS cap… Wan-Teh Chang
Re: [TLS] Cipher suite values to indicate TLS cap… Yoav Nir
Re: [TLS] Cipher suite values to indicate TLS cap… Yoav Nir
Re: [TLS] Cipher suite values to indicate TLS cap… Nikos Mavrogiannopoulos
Re: [TLS] Cipher suite values to indicate TLS cap… Geoffrey Keating
Re: [TLS] Cipher suite values to indicate TLS cap… Chris Richardson
Re: [TLS] Cipher suite values to indicate TLS cap… Tom Ritter
Re: [TLS] Cipher suite values to indicate TLS cap… Nikos Mavrogiannopoulos
Re: [TLS] Cipher suite values to indicate TLS cap… Adam Langley
Re: [TLS] Cipher suite values to indicate TLS cap… Nikos Mavrogiannopoulos
Re: [TLS] Cipher suite values to indicate TLS cap… Adam Langley
Re: [TLS] Cipher suite values to indicate TLS cap… Martin Rex