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

Hanno Böck <> Fri, 16 January 2015 20:03 UTC

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Date: Fri, 16 Jan 2015 21:03:27 +0100
From: Hanno Böck <>
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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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Recently Mozilla has disabled the now so-called protocol dance, which
makes adding another workaround (SCSV) pretty much obsolete:

And a few days ago mozilla dev Brian Smith tweetet this:
"Fx experiment to disable non-secure TLS version fallback is going even
better than expected. Starting to feel silly for delaying it so long."

I think this adds further evidence that adding another workaround layer
(SCSV) is the wrong thing to do. Instead browsers should just stop
doing weird things with protocols that compromise security and drop
the protocol dance completely.

(By the way: Has anyone thought what happens when people implement TLS
hardware that is version intolerant to versions > 1.2 and at the same
time send SCSV in the handshake? I'm pretty sure that at some point
some hardware will appear that does exactly that. Will we need another
SCSV standard for every TLS version then?)

Hanno Böck