Re: [TLS] An SCSV to stop TLS fallback.
Daniel Kahn Gillmor <dkg@fifthhorseman.net> Fri, 06 December 2013 18:45 UTC
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Date: Fri, 06 Dec 2013 13:45:31 -0500
From: Daniel Kahn Gillmor <dkg@fifthhorseman.net>
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Subject: Re: [TLS] An SCSV to stop TLS fallback.
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On 12/06/2013 01:25 PM, Martin Rex wrote: > So the use of the TLS_FALLBACK_SCSV will either *NOT* affect the rest > of the TLS protocol not at all, or cause a fatal handshake failure. > And very few, if any at all, of the situations where the handshake fails, > will be instances of an active attack. This is probably also true of X.509 certificate validation failure as well, since there are more self-signed or expired certificates in active use than there are active MITM attackers. Are you suggesting that TLS would be better off not checking certificate validity? > And it remains extremely > questionable, when the handshake would succeed, that the attacker > will gain anything at all. What the attacker can gain presumably depends on what features the client is willing to sacrifice during fallback. Presumably, the client gives up specific features of the newer versions: e.g. AEAD, when falling back below TLS 1.2, or possibly all TLS extensions for fallback all the way to SSLv3 (to accomodate old extension-intolerant SSLv3 servers). It looks like you're saying that none of these more modern features are useful tools in defending against an active attacker. Do you really think that? --dkg
- Re: [TLS] An SCSV to stop TLS fallback. Adam Langley
- Re: [TLS] An SCSV to stop TLS fallback. Adam Langley
- [TLS] An SCSV to stop TLS fallback. Adam Langley
- Re: [TLS] An SCSV to stop TLS fallback. Watson Ladd
- Re: [TLS] An SCSV to stop TLS fallback. Adam Langley
- Re: [TLS] An SCSV to stop TLS fallback. Andy Wilson
- Re: [TLS] An SCSV to stop TLS fallback. Yngve N. Pettersen
- Re: [TLS] An SCSV to stop TLS fallback. Martin Rex
- Re: [TLS] An SCSV to stop TLS fallback. Trevor Perrin
- Re: [TLS] An SCSV to stop TLS fallback. Adam Langley
- Re: [TLS] An SCSV to stop TLS fallback. Adam Langley
- Re: [TLS] An SCSV to stop TLS fallback. Martin Rex
- Re: [TLS] An SCSV to stop TLS fallback. Trevor Perrin
- Re: [TLS] An SCSV to stop TLS fallback. Watson Ladd
- Re: [TLS] An SCSV to stop TLS fallback. Brian Smith
- Re: [TLS] An SCSV to stop TLS fallback. Bodo Moeller
- Re: [TLS] An SCSV to stop TLS fallback. Adam Langley
- Re: [TLS] An SCSV to stop TLS fallback. Adam Langley
- Re: [TLS] An SCSV to stop TLS fallback. Adam Langley
- Re: [TLS] An SCSV to stop TLS fallback. Bodo Moeller
- Re: [TLS] An SCSV to stop TLS fallback. Jack Lloyd
- Re: [TLS] An SCSV to stop TLS fallback. Manger, James H
- Re: [TLS] An SCSV to stop TLS fallback. Wan-Teh Chang
- Re: [TLS] An SCSV to stop TLS fallback. Bodo Moeller
- Re: [TLS] An SCSV to stop TLS fallback. Wan-Teh Chang
- Re: [TLS] An SCSV to stop TLS fallback. Manuel Pégourié-Gonnard
- Re: [TLS] An SCSV to stop TLS fallback. Adam Langley
- Re: [TLS] An SCSV to stop TLS fallback. Bodo Moeller
- Re: [TLS] An SCSV to stop TLS fallback. Marsh Ray
- Re: [TLS] An SCSV to stop TLS fallback. Douglas Stebila
- Re: [TLS] An SCSV to stop TLS fallback. Yngve N. Pettersen
- Re: [TLS] An SCSV to stop TLS fallback. Yngve N. Pettersen
- Re: [TLS] An SCSV to stop TLS fallback. James Cloos
- Re: [TLS] An SCSV to stop TLS fallback. Yngve N. Pettersen
- Re: [TLS] An SCSV to stop TLS fallback. Manuel Pégourié-Gonnard
- Re: [TLS] An SCSV to stop TLS fallback. Bodo Moeller
- Re: [TLS] An SCSV to stop TLS fallback. Marsh Ray
- Re: [TLS] An SCSV to stop TLS fallback. Bodo Moeller
- Re: [TLS] An SCSV to stop TLS fallback. Martin Rex
- Re: [TLS] An SCSV to stop TLS fallback. Adam Langley
- Re: [TLS] An SCSV to stop TLS fallback. Daniel Kahn Gillmor
- Re: [TLS] An SCSV to stop TLS fallback. Brian Smith
- Re: [TLS] An SCSV to stop TLS fallback. Ralf Skyper Kaiser
- Re: [TLS] An SCSV to stop TLS fallback. Martin Rex
- Re: [TLS] An SCSV to stop TLS fallback. Martin Rex
- Re: [TLS] An SCSV to stop TLS fallback. Watson Ladd
- Re: [TLS] An SCSV to stop TLS fallback. Martin Rex
- Re: [TLS] An SCSV to stop TLS fallback. Watson Ladd
- Re: [TLS] An SCSV to stop TLS fallback. Martin Rex
- Re: [TLS] An SCSV to stop TLS fallback. Yaron Sheffer
- Re: [TLS] An SCSV to stop TLS fallback. Ralf Skyper Kaiser
- Re: [TLS] An SCSV to stop TLS fallback. Yaron Sheffer
- Re: [TLS] An SCSV to stop TLS fallback. Ralf Skyper Kaiser
- Re: [TLS] An SCSV to stop TLS fallback. Manuel Pégourié-Gonnard
- Re: [TLS] An SCSV to stop TLS fallback. Ralf Skyper Kaiser
- Re: [TLS] An SCSV to stop TLS fallback. Bodo Moeller