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From: demerphq <demerphq@gmail.com>
To: Sitaram Chamarty <sitaramc@gmail.com>
Cc: "brian m. carlson" <sandals@crustytoothpaste.net>,
	Johannes Schindelin <Johannes.Schindelin@gmx.de>,
	Jonathan Nieder <jrnieder@gmail.com>, Git <git@vger.kernel.org>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	agl@google.com, keccak@noekeon.org
Subject: Re: Hash algorithm analysis
Date: Mon, 23 Jul 2018 14:55:21 +0200
Message-ID: <CANgJU+U+XEpBLQAZKkNTqcAKTfKqMStNBk2pr7wjLq2q+BELww@mail.gmail.com> (raw)
In-Reply-To: <98111891-a605-1cfd-e92b-a3b5b4186ac2@gmail.com>

On Mon, 23 Jul 2018 at 14:48, Sitaram Chamarty <sitaramc@gmail.com> wrote:
> On 07/23/2018 06:10 PM, demerphq wrote:
> > On Sun, 22 Jul 2018 at 01:59, brian m. carlson
> > <sandals@crustytoothpaste.net> 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/"

  reply index

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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