From: demerphq <email@example.com> To: Sitaram Chamarty <firstname.lastname@example.org> Cc: "brian m. carlson" <email@example.com>, Johannes Schindelin <Johannes.Schindelin@gmx.de>, Jonathan Nieder <firstname.lastname@example.org>, Git <email@example.com>, Linus Torvalds <firstname.lastname@example.org>, email@example.com, firstname.lastname@example.org Subject: Re: Hash algorithm analysis Date: Mon, 23 Jul 2018 14:55:21 +0200 [thread overview] Message-ID: <CANgJU+U+XEpBLQAZKkNTqcAKTfKqMStNBk2pr7wjLq2q+BELww@mail.gmail.com> (raw) In-Reply-To: <email@example.com> On Mon, 23 Jul 2018 at 14:48, Sitaram Chamarty <firstname.lastname@example.org> wrote: > On 07/23/2018 06:10 PM, demerphq wrote: > > On Sun, 22 Jul 2018 at 01:59, brian m. carlson > > <email@example.com> wrote: > >> I will admit that I don't love making this decision by myself, because > >> right now, whatever I pick, somebody is going to be unhappy. I want to > >> state, unambiguously, that I'm trying to make a decision that is in the > >> interests of the Git Project, the community, and our users. > >> > >> I'm happy to wait a few more days to see if a consensus develops; if so, > >> I'll follow it. If we haven't come to one by, say, Wednesday, I'll make > >> a decision and write my patches accordingly. The community is free, as > >> always, to reject my patches if taking them is not in the interest of > >> the project. > > > > Hi Brian. > > > > I do not envy you this decision. > > > > Personally I would aim towards pushing this decision out to the git > > user base and facilitating things so we can choose whatever hash > > function (and config) we wish, including ones not invented yet. > > > > Failing that I would aim towards a hashing strategy which has the most > > flexibility. Keccak for instance has the interesting property that its > > security level is tunable, and that it can produce aribitrarily long > > hashes. Leaving aside other concerns raised elsewhere in this thread, > > these two features alone seem to make it a superior choice for an > > initial implementation. You can find bugs by selecting unusual hash > > sizes, including very long ones, and you can provide ways to tune the > > function to peoples security and speed preferences. Someone really > > paranoid can specify an unusually large round count and a very long > > hash. > > > > Also frankly I keep thinking that the ability to arbitrarily extend > > the hash size has to be useful /somewhere/ in git. > > I would not suggest arbitrarily long hashes. Not only would it > complicate a lot of code, it is not clear that it has any real benefit. It has the benefit of armoring the code for the *next* hash change, and making it clear that such decisions are arbitrary and should not be depended on. > Plus, the code contortions required to support arbitrarily long hashes > would be more susceptible to potential bugs and exploits, simply by > being more complex code. Why take chances? I think the benefits would outweight the risks. > I would suggest (a) hash size of 256 bits and (b) choice of any hash > function that can produce such a hash. If people feel strongly that 256 > bits may also turn out to be too small (really?) then a choice of 256 or > 512, but not arbitrary sizes. I am aware of too many systems that cannot change their size and are locked into woefully bad decisions that were made long ago to buy this. Making it a per-repo option, would eliminate assumptions and make for a more secure and flexible tool. Anyway, I am not going to do the work so my opinion is worth the price of the paper I sent it on. :-) cheers, Yves -- perl -Mre=debug -e "/just|another|perl|hacker/"
next prev parent reply other threads:[~2018-07-23 12:55 UTC|newest] Thread overview: 66+ messages / expand[flat|nested] mbox.gz Atom feed top 2018-06-09 20:56 State of NewHash work, future directions, and discussion brian m. carlson 2018-06-09 21:26 ` Ævar Arnfjörð Bjarmason 2018-06-09 22:49 ` Hash algorithm analysis brian m. carlson 2018-06-11 19:29 ` Jonathan Nieder 2018-06-11 20:20 ` Linus Torvalds 2018-06-11 23:27 ` Ævar Arnfjörð Bjarmason 2018-06-12 0:11 ` David Lang 2018-06-12 0:45 ` Linus Torvalds 2018-06-11 22:35 ` brian m. carlson 2018-06-12 16:21 ` Gilles Van Assche 2018-06-13 23:58 ` brian m. carlson 2018-06-15 10:33 ` Gilles Van Assche 2018-07-20 21:52 ` brian m. carlson 2018-07-21 0:31 ` Jonathan Nieder 2018-07-21 19:52 ` Ævar Arnfjörð Bjarmason 2018-07-21 20:25 ` brian m. carlson 2018-07-21 22:38 ` Johannes Schindelin 2018-07-21 23:09 ` Linus Torvalds 2018-07-21 23:59 ` brian m. carlson 2018-07-22 9:34 ` Eric Deplagne 2018-07-22 14:21 ` brian m. carlson 2018-07-22 14:55 ` Eric Deplagne 2018-07-26 10:05 ` Johannes Schindelin 2018-07-22 15:23 ` Joan Daemen 2018-07-22 18:54 ` Adam Langley 2018-07-26 10:31 ` Johannes Schindelin 2018-07-23 12:40 ` demerphq 2018-07-23 12:48 ` Sitaram Chamarty 2018-07-23 12:55 ` demerphq [this message] 2018-07-23 18:23 ` Linus Torvalds 2018-07-23 17:57 ` Stefan Beller 2018-07-23 18:35 ` Jonathan Nieder 2018-07-24 19:01 ` Edward Thomson 2018-07-24 20:31 ` Linus Torvalds 2018-07-24 20:49 ` Jonathan Nieder 2018-07-24 21:13 ` Junio C Hamano 2018-07-24 22:10 ` brian m. carlson 2018-07-30 9:06 ` Johannes Schindelin 2018-07-30 20:01 ` Dan Shumow 2018-08-03 2:57 ` Jonathan Nieder 2018-09-18 15:18 ` Joan Daemen 2018-09-18 15:32 ` Jonathan Nieder 2018-09-18 16:50 ` Linus Torvalds 2018-07-25 8:30 ` [PATCH 0/2] document that NewHash is now SHA-256 Ævar Arnfjörð Bjarmason 2018-07-25 8:30 ` [PATCH 1/2] doc hash-function-transition: note the lack of a changelog Ævar Arnfjörð Bjarmason 2018-07-25 8:30 ` [PATCH 2/2] doc hash-function-transition: pick SHA-256 as NewHash Ævar Arnfjörð Bjarmason 2018-07-25 16:45 ` Junio C Hamano 2018-07-25 17:25 ` Jonathan Nieder 2018-07-25 21:32 ` Junio C Hamano 2018-07-26 13:41 ` [PATCH v2 " Ævar Arnfjörð Bjarmason 2018-08-03 7:20 ` Jonathan Nieder 2018-08-03 16:40 ` Junio C Hamano 2018-08-03 17:01 ` Linus Torvalds 2018-08-03 16:42 ` Linus Torvalds 2018-08-03 17:43 ` Ævar Arnfjörð Bjarmason 2018-08-04 8:52 ` Jonathan Nieder 2018-08-03 17:45 ` brian m. carlson 2018-07-25 22:56 ` [PATCH " brian m. carlson 2018-06-11 21:19 ` Hash algorithm analysis Ævar Arnfjörð Bjarmason 2018-06-21 8:20 ` Johannes Schindelin 2018-06-21 22:39 ` brian m. carlson 2018-06-11 18:09 ` State of NewHash work, future directions, and discussion Duy Nguyen 2018-06-12 1:28 ` brian m. carlson 2018-06-11 19:01 ` Jonathan Nieder 2018-06-12 2:28 ` brian m. carlson 2018-06-12 2:42 ` Jonathan Nieder
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