On Tuesday 12 January 2016 14:24:31 Martin Rex wrote: > Tony Arcieri wrote: > [ Charset UTF-8 unsupported, converting... ] > > > Peter Gutmann <pgut...@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
the problem stems from the fact that the same field is used for announcing support for signatures in ServerKeyExchange *and* for certificates provided by server. while SKE signatures could have easily been made mandatory to SHA-256 at least, the depreciation of SHA-1 signatures for certificates certainly wasn't possible at the time - only now we are closing on migration from them so, it was a _bad_ decision, but calling it a "braindead" one is a bit over the top, sorry -- Regards, Hubert Kario Senior Quality Engineer, QE BaseOS Security team Web: www.cz.redhat.com Red Hat Czech s.r.o., Purkyňova 99/71, 612 45, Brno, Czech Republic
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