Re: [TLS] draft-ietf-tls-cached-info-02 / New "Fast-Track" draft
Marsh Ray <marsh@extendedsubset.com> Wed, 24 February 2010 21:00 UTC
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Date: Wed, 24 Feb 2010 15:02:55 -0600
From: Marsh Ray <marsh@extendedsubset.com>
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To: "Kemp, David P." <DPKemp@missi.ncsc.mil>
References: <4B8407D7.9040207@briansmith.org> <C7AB19CF.88B9%stefan@aaa-sec.com><201002241753.o1OHrxuK015491@stingray.missi.ncsc.mil> <4B856F19.6080809@extendedsubset.com> <201002241950.o1OJonSH025171@stingray.missi.ncsc.mil>
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Cc: tls@ietf.org
Subject: Re: [TLS] draft-ietf-tls-cached-info-02 / New "Fast-Track" draft
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Kemp, David P. wrote: > Marsh Ray wrote: >> It will not be so fun to convince reviewers that "yes we're using >> SHA-1 but not in a way that really matters." >> >> If all you need is a 64-bit checksum for data-structure-style >> hashing and indexing, use any old old-fashioned checksum algorithm. >> >> >> This would be simple for everyone to implement and it clearly >> communicates your design intent (that the security of the design >> does not depend on any properties of this value's calculation). > > +1 in principle. > > But practically speaking, do you have any suggestions for well-known > non-cryptographic hash algorithms? Hmm, starting with http://en.wikipedia.org/wiki/List_of_hash_functions FNV seems like a good candidate. http://en.wikipedia.org/wiki/Fowler-Noll-Vo_hash_function Pros: * Wide existing usage: http://www.isthe.com/chongo/tech/comp/fnv/index.html#history * On that page they disclaim patents on it. * It is defined in power-of-two sizes from 32 to 1024 bits. * Something of an endorsement: "We experimetned with several different hash functions and found FNV has to be the best one." http://domino.watson.ibm.com/library/cyberdig.nsf/papers/2314E66547EF9CC5852576BE005F1E4F/$File/rc24939.pdf Cons: * Uses multiply. Probably not a big deal in practice. * Not (yet) referenceable in a formal standards doc. > A quick IANA search turned up > Kerberos checksums > http://www.iana.org/assignments/kerberos-parameters/kerberos-parameters.xhtml, > including CRC32 (4 octets), des-mac-k (8 octets), and several 16 > octet algorithms including MD4 and MD5. CRC64 doesn't seem to be so great with collisions: http://www.cs.ucl.ac.uk/staff/d.jones/crcnote.pdf The authors propose a better version. You could use a pair of (some variant of) CRC32, each preloaded with different values. This may not be any better than CRC64 though and may not be terribly efficient. > A search for other "hash", "mac", or "checksum" registries turned up > nothing new. > > It doesn't feel quite right to add a non-cryptographic checksum to > the RFC 5246 registry: > > enum { none(0), md5(1), sha1(2), sha224(3), sha256(4), sha384(5), > sha512(6), (255) } HashAlgorithm; > > so even if there were such an algorithm, permitting both it and > cryptographic hashes would be painful. Is it really necessary for this to be a flexible parameter? A implementation now has a choice: implement them all (including ones that are never used in practice), or risk not not being compatible somewhere. > I don't see an alternative that satisfies both "simple to implement" > and "clearly communicates intent". My care-abouts are 1) a common > interoperable algorithm and 2) bandwidth. Computation speed is > unimportant, There's always code size to consider. > so if everyone thinks sha256 will be cryptographically > viable for the foreseeable future and SHA-1 will soon be impossible > to get "approved", then sha256 truncated to 64 bits could be a > reasonable MUST-support algorithm. Now you'll have to explain why you're taking the output of an industrial-strength hash function and throwing away 3/4 of it. :-) Plus, it's wasted effort since collisions will be possible to find in any 64-bit hash function. - Marsh
- Re: [TLS] draft-ietf-tls-cached-info-02 / New "Fa… Brian Smith
- Re: [TLS] draft-ietf-tls-cached-info-02 / New "Fa… Simon Josefsson
- Re: [TLS] draft-ietf-tls-cached-info-02 / New "Fa… Adam Langley
- Re: [TLS] draft-ietf-tls-cached-info-02 / New "Fa… Brian Smith
- Re: [TLS] draft-ietf-tls-cached-info-02 / New "Fa… Nikos Mavrogiannopoulos
- Re: [TLS] draft-ietf-tls-cached-info-02 / New "Fa… Adam Langley
- Re: [TLS] draft-ietf-tls-cached-info-02 / New "Fa… Michael D'Errico
- Re: [TLS] draft-ietf-tls-cached-info-02 / New "Fa… Nikos Mavrogiannopoulos
- Re: [TLS] Android's cut-through mode & "RequestTi… Brian Smith
- [TLS] Stream multiplexing extension RE: SPDY / Ne… Brian Smith
- Re: [TLS] draft-ietf-tls-cached-info-02 / New "Fa… Brian Smith
- [TLS] TLS Performance (was Re: draft-ietf-tls-cac… Michael D'Errico
- Re: [TLS] draft-ietf-tls-cached-info-02 / New "Fa… Stefan Santesson
- Re: [TLS] draft-ietf-tls-cached-info-02 / New "Fa… Adam Langley
- Re: [TLS] draft-ietf-tls-cached-info-02 / New "Fa… Stefan Santesson
- Re: [TLS] draft-ietf-tls-cached-info-02 / New "Fa… Stefan Santesson
- Re: [TLS] draft-ietf-tls-cached-info-02 / New "Fa… Adam Langley
- Re: [TLS] draft-ietf-tls-cached-info-02 / New "Fa… Adam Langley
- Re: [TLS] draft-ietf-tls-cached-info-02 / New "Fa… Brian Smith
- Re: [TLS] draft-ietf-tls-cached-info-02 / New "Fa… Brian Smith
- Re: [TLS] draft-ietf-tls-cached-info-02 / New "Fa… Brian Smith
- Re: [TLS] draft-ietf-tls-cached-info-02 / New "Fa… Kemp, David P.
- Re: [TLS] draft-ietf-tls-cached-info-02 / New "Fa… Stefan Santesson
- Re: [TLS] draft-ietf-tls-cached-info-02 / New "Fa… Martin Rex
- Re: [TLS] draft-ietf-tls-cached-info-02 / New "Fa… Brian Smith
- [TLS] Cached-info substitution Stefan Santesson
- Re: [TLS] draft-ietf-tls-cached-info-02 / New "Fa… Stefan Santesson
- Re: [TLS] draft-ietf-tls-cached-info-02 / New "Fa… Kemp, David P.
- Re: [TLS] Cached-info substitution Brian Smith
- Re: [TLS] draft-ietf-tls-cached-info-02 / New "Fa… Martin Rex
- Re: [TLS] Cached-info substitution Adam Langley
- Re: [TLS] Cached-info substitution Brian Smith
- Re: [TLS] Cached-info substitution Adam Langley
- Re: [TLS] draft-ietf-tls-cached-info-02 / New "Fa… Brian Smith
- Re: [TLS] Cached-info substitution Stefan Santesson
- Re: [TLS] draft-ietf-tls-cached-info-02 / New "Fa… Stefan Santesson
- Re: [TLS] draft-ietf-tls-cached-info-02 / New "Fa… Martin Rex
- Re: [TLS] draft-ietf-tls-cached-info-02 / New "Fa… Brian Smith
- Re: [TLS] draft-ietf-tls-cached-info-02 / New "Fa… Martin Rex
- Re: [TLS] draft-ietf-tls-cached-info-02 / New "Fa… Kemp, David P.
- Re: [TLS] draft-ietf-tls-cached-info-02 / New "Fa… Martin Rex
- Re: [TLS] draft-ietf-tls-cached-info-02 / New "Fa… Stefan Santesson
- Re: [TLS] draft-ietf-tls-cached-info-02 / New "Fa… Stefan Santesson
- Re: [TLS] draft-ietf-tls-cached-info-02 / New "Fa… Martin Rex
- [TLS] RFC 5077 (was Re: draft-ietf-tls-cached-inf… Michael D'Errico
- Re: [TLS] Cached-info substitution Adam Langley
- Re: [TLS] Cached-info substitution Wan-Teh Chang
- Re: [TLS] Cached-info substitution Stefan Santesson
- Re: [TLS] draft-ietf-tls-cached-info-02 / New "Fa… Simon Josefsson
- Re: [TLS] draft-ietf-tls-cached-info-02 / New "Fa… Martin Rex
- Re: [TLS] draft-ietf-tls-cached-info-02 / New "Fa… Brian Smith
- Re: [TLS] draft-ietf-tls-cached-info-02 / New "Fa… Brian Smith
- Re: [TLS] draft-ietf-tls-cached-info-02 / New "Fa… Stefan Santesson
- Re: [TLS] draft-ietf-tls-cached-info-02 / New "Fa… Kemp, David P.
- Re: [TLS] draft-ietf-tls-cached-info-02 / New "Fa… Marsh Ray
- Re: [TLS] [POSSIBLE SPAM] Re: draft-ietf-tls-cach… Kemp, David P.
- Re: [TLS] draft-ietf-tls-cached-info-02 / New "Fa… Marsh Ray
- Re: [TLS] draft-ietf-tls-cached-info-02 / New "Fa… Yoav Nir
- Re: [TLS] draft-ietf-tls-cached-info-02 / New "Fa… Stefan Santesson
- Re: [TLS] draft-ietf-tls-cached-info-02 / New "Fa… Simon Josefsson
- Re: [TLS] draft-ietf-tls-cached-info-02 / New "Fa… Brian Smith
- Re: [TLS] draft-ietf-tls-cached-info-02 / New "Fa… Stefan Santesson
- Re: [TLS] draft-ietf-tls-cached-info-02 / New "Fa… Brian Smith
- Re: [TLS] draft-ietf-tls-cached-info-02 / New "Fa… Martin Rex
- Re: [TLS] draft-ietf-tls-cached-info-02 / New "Fa… Stefan Santesson
- Re: [TLS] draft-ietf-tls-cached-info-02 / New "Fa… Simon Josefsson
- Re: [TLS] draft-ietf-tls-cached-info-02 / New "Fa… Simon Josefsson
- Re: [TLS] draft-ietf-tls-cached-info-02 / New "Fa… Stefan Santesson
- Re: [TLS] draft-ietf-tls-cached-info-02 / New "Fa… Stefan Santesson
- Re: [TLS] draft-ietf-tls-cached-info-02 / New "Fa… Joseph Salowey (jsalowey)
- Re: [TLS] draft-ietf-tls-cached-info-02 / New "Fa… Stefan Santesson
- Re: [TLS] draft-ietf-tls-cached-info-02 / New "Fa… Brian Smith
- Re: [TLS] draft-ietf-tls-cached-info-02 / New "Fa… Brian Smith
- Re: [TLS] draft-ietf-tls-cached-info-02 / New "Fa… Martin Rex
- Re: [TLS] draft-ietf-tls-cached-info-02 / New "Fa… Simon Josefsson
- Re: [TLS] draft-ietf-tls-cached-info-02 / New "Fa… Donald Eastlake
- Re: [TLS] draft-ietf-tls-cached-info-02 / New "Fa… Joseph Salowey (jsalowey)
- Re: [TLS] draft-ietf-tls-cached-info-02 / New "Fa… Stefan Santesson
- Re: [TLS] draft-ietf-tls-cached-info-02 / New "Fa… Marsh Ray
- Re: [TLS] draft-ietf-tls-cached-info-02 / New "Fa… Simon Josefsson
- Re: [TLS] draft-ietf-tls-cached-info-02 / New "Fa… Stefan Santesson
- Re: [TLS] draft-ietf-tls-cached-info-02 / New "Fa… Adam Langley
- Re: [TLS] draft-ietf-tls-cached-info-02 / New "Fa… Michael D'Errico