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From: Junio C Hamano <gitster@pobox.com>
To: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Cc: git@vger.kernel.org,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Edward Thomson <ethomson@edwardthomson.com>,
	"brian m . carlson" <sandals@crustytoothpaste.net>,
	Jonathan Nieder <jrnieder@gmail.com>,
	Johannes Schindelin <Johannes.Schindelin@gmx.de>,
	demerphq <demerphq@gmail.com>, Adam Langley <agl@google.com>,
	keccak@noekeon.org
Subject: Re: [PATCH 2/2] doc hash-function-transition: pick SHA-256 as NewHash
Date: Wed, 25 Jul 2018 09:45:52 -0700
Message-ID: <xmqq4lgnw9fj.fsf@gitster-ct.c.googlers.com> (raw)
In-Reply-To: <20180725083024.16131-3-avarab@gmail.com>

Ævar Arnfjörð Bjarmason  <avarab@gmail.com> writes:

> @@ -125,19 +122,19 @@ Detailed Design
>  ---------------
>  Repository format extension
>  ~~~~~~~~~~~~~~~~~~~~~~~~~~~
> -A NewHash repository uses repository format version `1` (see
> +A SHA-256 repository uses repository format version `1` (see
>  Documentation/technical/repository-version.txt) with extensions
>  `objectFormat` and `compatObjectFormat`:
>  
>  	[core]
>  		repositoryFormatVersion = 1
>  	[extensions]
> -		objectFormat = newhash
> +		objectFormat = sha256
>  		compatObjectFormat = sha1

Whenever we said SHA1, somebody came and told us that the name of
the hash is SHA-1 (with dash).  Would we be nitpicker-prone in the
same way with "sha256" here?

> @@ -155,36 +152,36 @@ repository extensions.
>  Object names
>  ~~~~~~~~~~~~
>  Objects can be named by their 40 hexadecimal digit sha1-name or 64
> -hexadecimal digit newhash-name, plus names derived from those (see
> +hexadecimal digit sha256-name, plus names derived from those (see
>  gitrevisions(7)).

Seeing this hunk makes me respond to the above question with another
question: "having to write sha-256-name, sha-1-name, gpgsig-sha-256,
and sha-256-content is sort of ugly, no?"

I guess names with two dashes are not _too_ bad, so I dunno.

>  Selection of a New Hash
>  -----------------------
> @@ -611,6 +608,10 @@ collisions in 2^69 operations. In August they published details.
>  Luckily, no practical demonstrations of a collision in full SHA-1 were
>  published until 10 years later, in 2017.
>  
> +It was decided that Git needed to transition to a new hash
> +function. Initially no decision was made as to what function this was,
> +the "NewHash" placeholder name was picked to describe it.
> +
>  The hash function NewHash to replace SHA-1 should be stronger than
>  SHA-1 was: we would like it to be trustworthy and useful in practice
>  for at least 10 years.

This sentence needs a bit of updating to match the new paragraph
inserted above.  "should be stronger" is something said by those
who are still looking for one and/or trying to decide.  Perhaps
something like this?

	...
	the "NewHash" placeholder name was used to describe it.

	We wanted to choose a hash function to replace SHA-1 that is
	stronger than SHA-1 was, and would like it to be trustworthy
	and useful in practice for at least 10 years.

	Some other relevant properties we wanted in NewHash are:

> @@ -630,14 +631,19 @@ Some other relevant properties:
>  4. As a tiebreaker, the hash should be fast to compute (fortunately
>     many contenders are faster than SHA-1).
>  
> -Some hashes under consideration are SHA-256, SHA-512/256, SHA-256x16,
> +Some hashes under consideration were SHA-256, SHA-512/256, SHA-256x16,
>  K12, and BLAKE2bp-256.
>  
> +Eventually in July 2018 SHA-256 was chosen to be the NewHash. See the
> +thread starting at <20180609224913.GC38834@genre.crustytoothpaste.net>
> +for the discussion
> +(https://public-inbox.org/git/20180609224913.GC38834@genre.crustytoothpaste.net/)
> +


  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
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 [this message]
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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