Re: [TLS] Last Call: <draft-ietf-tls-downgrade-scsv-03.txt> (TLS Fallback Signaling Cipher Suite Value (SCSV) for Preventing Protocol Downgrade Attacks) to Proposed Standard

Nikos Mavrogiannopoulos <> Mon, 12 January 2015 09:16 UTC

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From: Nikos Mavrogiannopoulos <>
To: Stephen Farrell <>
Date: Mon, 12 Jan 2015 10:15:56 +0100
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Subject: Re: [TLS] Last Call: <draft-ietf-tls-downgrade-scsv-03.txt> (TLS Fallback Signaling Cipher Suite Value (SCSV) for Preventing Protocol Downgrade Attacks) to Proposed Standard
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On Sun, 2015-01-11 at 00:48 +0000, Stephen Farrell wrote:
> Hi Nikos,
> >> The IESG plans to make a decision in the next few weeks, and solicits
> >> final comments on this action. Please send substantive comments to the
> >> mailing lists by 2015-01-23. Exceptionally, comments may be
> >> sent to instead. In either case, please retain the
> >> beginning of the Subject line to allow automated sorting.
> >>    This document defines a Signaling Cipher Suite Value (SCSV) that
> >>    prevents protocol downgrade attacks on the Transport Layer Security
> >>    (TLS) protocol.  It updates RFC 2246, RFC 4346, and RFC 5246.
> > The "TLS Fallback Signaling Cipher Suite" fix cannot be a proposed standard. 
> > The mechanism it fixes (the browser's special downgrade of TLS) is not an IETF
> > protocol, nor related to the TLS WG. Making this a proposed standard, would 
> > imply that the flawed technique is into standards track. 
> I don't believe that that last conclusion follows. AFIAK there is
> nothing to prevent the IETF standardising a fix for someone else's
> or even our own past mistakes(*) even when those mistakes are not
> on the standards track. And if in fact stardardising the "fix"
> improves the Internet, then we should do that as the set of folks
> responsible for this technology. (If doing so has IETF consensus.)

It's not up to me to say whether there was consensus for this draft or
not. I voiced my opinion against that draft. However, if you think that
this has to be on standards track, please provide at least some
argumentation for it. 

As far as I understand, this fix exists because Microsoft, Google and
Mozilla cannot coordinate and drop their insecure negotiation of TLS.