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From: Jonathan Nieder <jrnieder@gmail.com>
To: Joan Daemen <jda@noekeon.org>
Cc: Dan Shumow <danshu@microsoft.com>,
	Johannes Schindelin <Johannes.Schindelin@gmx.de>,
	"brian m. carlson" <sandals@crustytoothpaste.net>,
	Junio C Hamano <gitster@pobox.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Edward Thomson <ethomson@edwardthomson.com>,
	Git Mailing List <git@vger.kernel.org>,
	demerphq <demerphq@gmail.com>, Adam Langley <agl@google.com>
Subject: Re: Hash algorithm analysis
Date: Tue, 18 Sep 2018 08:32:10 -0700
Message-ID: <20180918153210.GA133875@aiede.svl.corp.google.com> (raw)
In-Reply-To: <64c1fc82-8830-bd62-7cc6-ef76ad06f6d5@noekeon.org>

Hi,

A quick note.

Joan Daemen wrote:

> when going over my todo list I was confronted with the mail of Dan
> Shumow on the successor of SHA-1 for git. I know the decision was
> made and it is not my intention to change it, but please see below
> some comments on Dan's arguments.

When the time comes for the next hash change in Git, it will be useful
to be able to look back over this discussion.  Thanks for adding
details.

[...]
> On 30/07/2018 22:01, Dan Shumow wrote:

>> So, I also want to state my biases in favor of SHA2 as an employee
>> of Microsoft. [...] As such, and reflecting this bias, in the
>> internal discussions that Johannes alluded to, SHA2 and SHA3 were
>> the primary suggestions.  There was a slight preference for SHA2
>> because SHA3 is not exposed through the windows cryptographic APIs
>> (though Git does not use those, so this is a nonissue for this
>> discussion.)
>
> We find it cynical to bring up a Microsoft-internal argument that is
> actually not relevant to Git.

On the contrary, I am quite grateful that Dan was up front about where
his preference comes from, *especially* when the reasons are not
relevant to Git.  It is useful background for better understanding his
rationale and understanding the ramifications for some subset of
users.

In other words, consider someone active in the Git project that
disagrees with the decision to use SHA2.  This explanation by Dan can
help such a person understand where the disagreement is coming from
and whether we are making the decision for the wrong reasons (because
Git on Windows does not even use those APIs).

[...]
> 3) The relatively large state in the sponge construction increases
> the generic strength against attacks when the input contains
> redundancy or has a certain form. For instance, if the input is
> restricted to be text in ASCII (such as source code), then the
> collision-resistance grows higher than the nominal 2^{c/2}. Such an
> effect does not exist with narrow-pipe Merkle-Damgård. (This may be
> what Linus had intuitively in mind.)

Interesting.

[...]
> [2] Daniel J. Bernstein, Cost analysis of hash collisions: Will
> quantum computers make SHARCS obsolete? Workshop Record of
> SHARCS'09.

I remember that paper!  Thanks for the pointer.

Sincerely,
Jonathan

  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
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 [this message]
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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