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
mrex@sap.com (Martin Rex) Mon, 19 January 2015 19:27 UTC
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To: "Salz, Rich" <rsalz@akamai.com>
Date: Mon, 19 Jan 2015 20:27:01 +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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Salz, Rich wrote: > I read your note very carefully. > It is a nice detailed list of things that could be improved. Permitting the server to continue the TLS handshake with ServerHello.server_version = (ClientHello.client_version +1) This would be an extremely small change, but a *HUGE* improvement to this proposal and make TLS handshakes _succeed_, i.e. promote interop. Should a TLS client be unsatisfied with the properties of the resulting TLS session, that client could still decide attempting a new/different handshake by proposing additional features in ClientHello (that should have never been absent from ClientHello in the first place). And this improvement is something that I could imagine implementing for our servers -- other than the currently specified knee-jerk-reaction. > > But I see no elucidation of any massive serious operational problems. > The I-D section you pointed to contains an answer. The current last call is a request to rubber-stamp the current fallback-scsv proposal, that wants to require from the server an unconditional knee-jerk-reaction and complete interop failure, onto the standards track. It is difficult to conceive a proposal that violates rfc2116 section 6 in a more serious fashion than the current fallback-scsv proposal -- and fixing this would be trivial (see above). It's not that suggestions to improvement to this proposal haven't been made. It's really disappointing to see this go _through_ the TLS WG and not seeing any improvement whatsoever, and then going straight to asking for rubber-stamping it. http://www.ietf.org/mail-archive/web/tls/current/msg11238.html http://www.ietf.org/mail-archive/web/tls/current/msg11221.html > > Many large network operators have rolled this out, and the net has > been pretty silent about any "tales of woe." If all of the parties that you care for already have this implemented, then there is no need to puslish this proposal on the standards track any more. So we don't have to find out how others implement this. I can easily remember the unfortunate outcome the last time that the TLS WG asked for anal behaviour (RSA premaster secret version check) and how much interop problems this caused in the installed base because one vendor decided to ship this unvalidated: http://www.ietf.org/mail-archive/web/tls/current/msg11226.html This particular handshake failure flaw has is known for > 3 years, and still has not been fixed on the platform that has by far the largest market share... No, I am *NOT* in favour of the IESG rubber-stamping another proposal for TLS handshake failures, when the alternative, allowing a handshake complete with better properties (such as suggested at the beginning of this message) will be trivial to achieve. Several implementers may be in the fortunate position to ignore or laugh at most end-users that see error messages or white pages in their browsers. And the firefox bug with the brittle client-side connection management that caused fallbacks to SSLv3 all by itself over several years: https://bugzilla.mozilla.org/show_bug.cgi?id=450280 is a good example of this. I'm not in such a position. We take support seriously, and we try to actually help customers overcome interoperability problems, even when such interop problems are caused by third party software or network middle-boxes. (We don't actually fix third-party software, but I do the analysis sufficiently thorough so that customers request patches for clear defects from the relevant vendors). -Martin
- [TLS] Last Call: <draft-ietf-tls-downgrade-scsv-0… The IESG
- Re: [TLS] Last Call: <draft-ietf-tls-downgrade-sc… Nikos Mavrogiannopoulos
- Re: [TLS] Last Call: <draft-ietf-tls-downgrade-sc… Salz, Rich
- Re: [TLS] Last Call: <draft-ietf-tls-downgrade-sc… Stephen Farrell
- Re: [TLS] Last Call: <draft-ietf-tls-downgrade-sc… Nikos Mavrogiannopoulos
- Re: [TLS] Last Call: <draft-ietf-tls-downgrade-sc… Stephen Farrell
- Re: [TLS] Last Call: <draft-ietf-tls-downgrade-sc… Bodo Moeller
- Re: [TLS] Last Call: <draft-ietf-tls-downgrade-sc… Nikos Mavrogiannopoulos
- Re: [TLS] Last Call: <draft-ietf-tls-downgrade-sc… Hanno Böck
- Re: [TLS] Last Call: <draft-ietf-tls-downgrade-sc… Yuhong Bao
- Re: [TLS] Last Call: <draft-ietf-tls-downgrade-sc… Adam Langley
- Re: [TLS] Last Call: <draft-ietf-tls-downgrade-sc… Andrei Popov
- Re: [TLS] Last Call: <draft-ietf-tls-downgrade-sc… Watson Ladd
- Re: [TLS] Last Call: <draft-ietf-tls-downgrade-sc… Bodo Moeller
- Re: [TLS] Last Call: <draft-ietf-tls-downgrade-sc… Brian Smith
- Re: [TLS] Last Call: <draft-ietf-tls-downgrade-sc… Martin Rex
- Re: [TLS] Last Call: <draft-ietf-tls-downgrade-sc… Martin Rex
- Re: [TLS] Last Call: <draft-ietf-tls-downgrade-sc… Jeffrey Walton
- Re: [TLS] Last Call: <draft-ietf-tls-downgrade-sc… Yoav Nir
- Re: [TLS] Last Call: <draft-ietf-tls-downgrade-sc… Eric Rescorla
- Re: [TLS] Last Call: <draft-ietf-tls-downgrade-sc… Salz, Rich
- Re: [TLS] Last Call: <draft-ietf-tls-downgrade-sc… Bodo Moeller
- Re: [TLS] Last Call: <draft-ietf-tls-downgrade-sc… Colm MacCárthaigh
- Re: [TLS] Last Call: <draft-ietf-tls-downgrade-sc… Yuhong Bao
- Re: [TLS] Last Call: <draft-ietf-tls-downgrade-sc… Martin Rex
- Re: [TLS] Last Call: <draft-ietf-tls-downgrade-sc… Salz, Rich
- Re: [TLS] Last Call: <draft-ietf-tls-downgrade-sc… Martin Rex
- Re: [TLS] Last Call: <draft-ietf-tls-downgrade-sc… Brian Smith
- Re: [TLS] Last Call: <draft-ietf-tls-downgrade-sc… Salz, Rich
- Re: [TLS] Last Call: <draft-ietf-tls-downgrade-sc… Martin Rex
- Re: [TLS] Last Call: <draft-ietf-tls-downgrade-sc… Martin Rex
- Re: [TLS] Last Call: <draft-ietf-tls-downgrade-sc… Xiaoyin Liu
- Re: [TLS] Last Call: <draft-ietf-tls-downgrade-sc… Yoav Nir
- Re: [TLS] Last Call: <draft-ietf-tls-downgrade-sc… Xiaoyin Liu
- Re: [TLS] Last Call: <draft-ietf-tls-downgrade-sc… Yoav Nir
- Re: [TLS] Last Call: <draft-ietf-tls-downgrade-sc… Nikos Mavrogiannopoulos
- Re: [TLS] Last Call: <draft-ietf-tls-downgrade-sc… Bodo Moeller
- Re: [TLS] Last Call: <draft-ietf-tls-downgrade-sc… Xiaoyin Liu
- Re: [TLS] Last Call: <draft-ietf-tls-downgrade-sc… Bodo Moeller
- Re: [TLS] Last Call: <draft-ietf-tls-downgrade-sc… Michael D'Errico
- Re: [TLS] Last Call: <draft-ietf-tls-downgrade-sc… Martin Rex
- Re: [TLS] Last Call: <draft-ietf-tls-downgrade-sc… Michael Clark
- Re: [TLS] Last Call: <draft-ietf-tls-downgrade-sc… Michael Clark
- Re: [TLS] Last Call: <draft-ietf-tls-downgrade-sc… Nikos Mavrogiannopoulos
- Re: [TLS] Last Call: <draft-ietf-tls-downgrade-sc… Michael Clark
- [TLS] advertizing the minimum TLS supported versi… Nikos Mavrogiannopoulos
- Re: [TLS] Last Call: <draft-ietf-tls-downgrade-sc… Jeffrey Walton
- Re: [TLS] Last Call: <draft-ietf-tls-downgrade-sc… Michael Clark
- Re: [TLS] advertizing the minimum TLS supported v… Michael Clark
- Re: [TLS] advertizing the minimum TLS supported v… Michael Clark
- Re: [TLS] Last Call: <draft-ietf-tls-downgrade-sc… Hubert Kario
- Re: [TLS] Last Call: <draft-ietf-tls-downgrade-sc… Henrik Grubbström
- Re: [TLS] Last Call: <draft-ietf-tls-downgrade-sc… Henrik Grubbström
- Re: [TLS] Last Call: <draft-ietf-tls-downgrade-sc… Bodo Moeller
- Re: [TLS] Last Call: <draft-ietf-tls-downgrade-sc… Bodo Moeller
- Re: [TLS] Last Call: <draft-ietf-tls-downgrade-sc… Dave Garrett
- Re: [TLS] Last Call: <draft-ietf-tls-downgrade-sc… Eric Rescorla
- Re: [TLS] Last Call: <draft-ietf-tls-downgrade-sc… Michael Clark
- Re: [TLS] Last Call: <draft-ietf-tls-downgrade-sc… Michael Clark
- Re: [TLS] Last Call: <draft-ietf-tls-downgrade-sc… Michael Clark
- Re: [TLS] Last Call: <draft-ietf-tls-downgrade-sc… Martin Rex
- Re: [TLS] Last Call: <draft-ietf-tls-downgrade-sc… Henrik Grubbström
- Re: [TLS] Last Call: <draft-ietf-tls-downgrade-sc… Nikos Mavrogiannopoulos
- Re: [TLS] Last Call: <draft-ietf-tls-downgrade-sc… Stephen Farrell
- Re: [TLS] Last Call: <draft-ietf-tls-downgrade-sc… Martin Rex