Re: [TLS] Deprecating TLS 1.0, 1.1 and SHA1 signature algorithms
mrex@sap.com (Martin Rex) Tue, 12 January 2016 13:24 UTC
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To: Tony Arcieri <bascule@gmail.com>
Date: Tue, 12 Jan 2016 14:24:31 +0100
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From: mrex@sap.com
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Subject: Re: [TLS] Deprecating TLS 1.0, 1.1 and SHA1 signature algorithms
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Tony Arcieri wrote: [ Charset UTF-8 unsupported, converting... ] > Peter Gutmann <pgut001@cs.auckland.ac.nz> wrote: > >> The vulnerabilities shown in the SLOTH paper were based on the fact that >> implementations still allow MD5 for authentication/integrity protection, >> even if (for example) it's explicitly disabled in the config. >> So the problem wasn't a fault in the protocol, it's buggy implementations >> (as it was for ones that allowed 512-bit keys, non-prime primes, >> and so on). Throwing out TLS 1.1 based on this seems rather premature. Actually no, the TLSv1.2 made a few terribly braindead design choices - newly introduce raw md5RSA digital signatures into TLSv1.2 in 2008 where all prior TLS protocol versions, including SSLv3 had been using the concatenation SHA-1||MD5 - making the sha1RSA rather than sha256RSA digital signature algorithm the default and mandatory-to-implement algorithm for use with TLSv1.2(!!) although it was well-known weaker than the algorithm (SHA-1||MD5) in all earlier TLS protocol versions, including SSLv3, and in spite of SHA-1 already being officially scheduled for end-of-life 2 years later (NIST, SP800-57 pt.1 rev2) This is ridiculous considering that SHA-256 is mandatory-to-use in the TLSv1.2 PRF. - failing to adjust the truncation of the HMAC output in the TLSv1.2 Finished handshake message to be at least half the size of the underlying hash function (SHA-256), see RFC 2104 Section 5: https://tools.ietf.org/html/rfc2104#section-5 > > My understanding is TLS 1.2 specifically was amended to allow MD5 > signatures even though this was not the case in previous TLS versions, or > at least that was the claim of the miTLS presenters on SLOTH at > RealWorldCrypto 2016. > > If this is the case, this seems like a big regression in TLS 1.2. And a fairly well-known & discussed regression, e.g. http://www.ietf.org/mail-archive/web/tls/current/msg10664.html that was subsequently removed in OpenSSL 1.0.1f in January 2014, i.e. 2 years before the SLOTH paper. I'm also wondering whether it might be misleading to lump the (in)significance of the currently known collisions for HMAC-SHA1 and HMAC-MD5 together with the (in)significance for (general, low-frequent) digital signatures and together with PKCS#10 & Certificate-issuance design flaw that enables a mere collision attack to achieve what would normally require a successful 2nd preimage attack. Compare the Security Considerations of rfc2104 for the (in)significance of current collision attacks for HMAC. https://tools.ietf.org/html/rfc2104#section-6 -Martin
- Re: [TLS] Deprecating TLS 1.0, 1.1 and SHA1 signa… David Benjamin
- [TLS] Deprecating TLS 1.0, 1.1 and SHA1 signature… Kurt Roeckx
- Re: [TLS] Deprecating TLS 1.0, 1.1 and SHA1 signa… Peter Gutmann
- Re: [TLS] Deprecating TLS 1.0, 1.1 and SHA1 signa… Tony Arcieri
- Re: [TLS] Deprecating TLS 1.0, 1.1 and SHA1 signa… David Benjamin
- Re: [TLS] Deprecating TLS 1.0, 1.1 and SHA1 signa… Peter Gutmann
- Re: [TLS] Deprecating TLS 1.0, 1.1 and SHA1 signa… Yuhong Bao
- Re: [TLS] Deprecating TLS 1.0, 1.1 and SHA1 signa… Andrei Popov
- Re: [TLS] Deprecating TLS 1.0, 1.1 and SHA1 signa… Viktor Dukhovni
- Re: [TLS] Deprecating TLS 1.0, 1.1 and SHA1 signa… Andrei Popov
- Re: [TLS] Deprecating TLS 1.0, 1.1 and SHA1 signa… Watson Ladd
- Re: [TLS] Deprecating TLS 1.0, 1.1 and SHA1 signa… Martin Thomson
- Re: [TLS] Deprecating TLS 1.0, 1.1 and SHA1 signa… Andrei Popov
- Re: [TLS] Deprecating TLS 1.0, 1.1 and SHA1 signa… Bill Frantz
- Re: [TLS] Deprecating TLS 1.0, 1.1 and SHA1 signa… Samuel Neves
- Re: [TLS] Deprecating TLS 1.0, 1.1 and SHA1 signa… Peter Gutmann
- Re: [TLS] Deprecating TLS 1.0, 1.1 and SHA1 signa… Watson Ladd
- Re: [TLS] Deprecating TLS 1.0, 1.1 and SHA1 signa… Peter Gutmann
- [TLS] MD5 diediedie (was Re: Deprecating TLS 1.0,… Dave Garrett
- Re: [TLS] MD5 diediedie (was Re: Deprecating TLS … Yuhong Bao
- Re: [TLS] MD5 diediedie (was Re: Deprecating TLS … Loganaden Velvindron
- Re: [TLS] MD5 diediedie (was Re: Deprecating TLS … Viktor Dukhovni
- Re: [TLS] MD5 diediedie (was Re: Deprecating TLS … Dave Garrett
- Re: [TLS] MD5 diediedie (was Re: Deprecating TLS … Tony Arcieri
- Re: [TLS] Deprecating TLS 1.0, 1.1 and SHA1 signa… Karthikeyan Bhargavan
- Re: [TLS] MD5 diediedie (was Re: Deprecating TLS … Stephen Farrell
- Re: [TLS] Deprecating TLS 1.0, 1.1 and SHA1 signa… Martin Rex
- Re: [TLS] MD5 diediedie (was Re: Deprecating TLS … Hubert Kario
- Re: [TLS] Deprecating TLS 1.0, 1.1 and SHA1 signa… Karthikeyan Bhargavan
- Re: [TLS] Deprecating TLS 1.0, 1.1 and SHA1 signa… Hubert Kario
- Re: [TLS] Deprecating TLS 1.0, 1.1 and SHA1 signa… Peter Gutmann
- Re: [TLS] Deprecating TLS 1.0, 1.1 and SHA1 signa… Hubert Kario
- Re: [TLS] MD5 diediedie (was Re: Deprecating TLS … Dave Garrett