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From: Jonathan Nieder <jrnieder@gmail.com>
To: Junio C Hamano <gitster@pobox.com>
Cc: Johannes Schindelin <Johannes.Schindelin@gmx.de>,
	Brandon Williams <bmwill@google.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Git Mailing List <git@vger.kernel.org>,
	Stefan Beller <sbeller@google.com>,
	jonathantanmy@google.com, Jeff King <peff@peff.net>,
	David Lang <david@lang.hm>,
	"brian m. carlson" <sandals@crustytoothpaste.net>
Subject: Re: RFC v3: Another proposed hash function transition plan
Date: Wed, 13 Sep 2017 15:27:31 -0700
Message-ID: <20170913222731.GQ27425@aiede.mtv.corp.google.com> (raw)
In-Reply-To: <xmqq377q1c0g.fsf@gitster.mtv.corp.google.com>

Junio C Hamano wrote:

> In the proposed transition plan, the treatment of various signatures
> (deliberately) makes the conversion not quite roundtrip.

That's not precisely true.  Details below.

> When existing SHA-1 history in individual clones are converted to
> NewHash, we obviously cannot re-sign the corresponding NewHash
> contents with the same PGP key, so these converted objects will
> carry only signature on SHA-1 contents.  They can still be validated
> when they are exported back to SHA-1 world via the fetch/push
> protocol, and can be validated locally by converting them back to
> SHA-1 contents and then passing the result to gpgv.

Correct.

> The plan also states, if I remember what I read correctly, that
> newly created and signed objects (this includes signed commits and
> signed tags; mergetags merely carry over what the tag object that
> was merged was signed with, so we do not have to worry about them
> unless the resulting commit that has mergetag is signed itself, but
> that is already covered by how we handle signed commits) would be
> signed both for NewHash contents and its corresponding SHA-1
> contents (after internally convering it to SHA-1 contents).

Also correct.

> would allow us to strip the signature over NewHash contents and
> derive the SHA-1 contents to be shown to the outside world while
> migration is going on and I'd imagine it would be a good practice;
> it would allow us to sign something that allows everybody to verify,
> when some participants of the project are not yet NewHash capable.

The NewHash-based signature is included in the SHA-1 content as well,
for the sake of round-tripping.  It is not stripped out.

> But the signing over SHA-1 contents has to stop at some point, when
> everybody's Git becomes completely unaware of SHA-1.  We may want to
> have a guideline in the transition plan to (1) encourage signing for
> both for quite some time, and (2) the criteria for us to decide when
> to stop.

Yes, spelling out a rough schedule is a good idea.  I'll add that.

A version of Git that is aware of NewHash should be able to verify
NewHash signatures even for users that are using SHA-1 locally for the
sake of faster fetches and pushes to SHA-1 based peers.

In addition to a new enough Git, this requires the translation table
to translate to NewHash to be present.

So the criterion (2) is largely based on how up-to-date the Git used
by users wanting to verify signatures is and whether they are willing
to tolerate the performance implications of having a translation
table.  My hope is that when communicating with peers using the same
hash function, the translation table will not add too much performance
overhead.

Thank you,
Jonathan

  reply index

Thread overview: 113+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-03-04  1:12 RFC: " Jonathan Nieder
2017-03-05  2:35 ` Linus Torvalds
2017-03-06  0:26   ` brian m. carlson
2017-03-06 18:24     ` Brandon Williams
2017-06-15 10:30       ` Which hash function to use, was " Johannes Schindelin
2017-06-15 11:05         ` Mike Hommey
2017-06-15 13:01           ` Jeff King
2017-06-15 16:30             ` Ævar Arnfjörð Bjarmason
2017-06-15 19:34               ` Johannes Schindelin
2017-06-15 21:59                 ` Adam Langley
2017-06-15 22:41                   ` brian m. carlson
2017-06-15 23:36                     ` Ævar Arnfjörð Bjarmason
2017-06-16  0:17                       ` brian m. carlson
2017-06-16  6:25                         ` Ævar Arnfjörð Bjarmason
2017-06-16 13:24                           ` Johannes Schindelin
2017-06-16 17:38                             ` Adam Langley
2017-06-16 20:52                               ` Junio C Hamano
2017-06-16 21:12                                 ` Junio C Hamano
2017-06-16 21:24                                   ` Jonathan Nieder
2017-06-16 21:39                                     ` Ævar Arnfjörð Bjarmason
2017-06-16 20:42                             ` Jeff King
2017-06-19  9:26                               ` Johannes Schindelin
2017-06-15 21:10             ` Mike Hommey
2017-06-16  4:30               ` Jeff King
2017-06-15 17:36         ` Brandon Williams
2017-06-15 19:20           ` Junio C Hamano
2017-06-15 19:13         ` Jonathan Nieder
2017-03-07  0:17   ` RFC v3: " Jonathan Nieder
2017-03-09 19:14     ` Shawn Pearce
2017-03-09 20:24       ` Jonathan Nieder
2017-03-10 19:38         ` Jeff King
2017-03-10 19:55           ` Jonathan Nieder
2017-09-28  4:43       ` [PATCH v4] technical doc: add a design doc for hash function transition Jonathan Nieder
2017-09-29  6:06         ` Junio C Hamano
2017-09-29  8:09           ` Junio C Hamano
2017-09-29 17:34           ` Jonathan Nieder
2017-10-02  8:25             ` Junio C Hamano
2017-10-02 19:41             ` Jason Cooper
2017-10-02  9:02         ` Junio C Hamano
2017-10-02 19:23         ` Jason Cooper
2017-10-03  5:40         ` Junio C Hamano
2017-10-03 13:08           ` Jason Cooper
2017-10-04  1:44         ` Junio C Hamano
2017-09-06  6:28     ` RFC v3: Another proposed hash function transition plan Junio C Hamano
2017-09-08  2:40       ` Junio C Hamano
2017-09-08  3:34         ` Jeff King
2017-09-11 18:59         ` Brandon Williams
2017-09-13 12:05           ` Johannes Schindelin
2017-09-13 13:43             ` demerphq
2017-09-13 22:51               ` Jonathan Nieder
2017-09-14 18:26                 ` Johannes Schindelin
2017-09-14 18:40                   ` Jonathan Nieder
2017-09-14 22:09                     ` Johannes Schindelin
2017-09-13 23:30               ` Linus Torvalds
2017-09-14 18:45                 ` Johannes Schindelin
2017-09-18 12:17                   ` Gilles Van Assche
2017-09-18 22:16                     ` Johannes Schindelin
2017-09-19 16:45                       ` Gilles Van Assche
2017-09-29 13:17                         ` Johannes Schindelin
2017-09-29 14:54                           ` Joan Daemen
2017-09-29 22:33                             ` Johannes Schindelin
2017-09-30 22:02                               ` Joan Daemen
2017-10-02 14:26                                 ` Johannes Schindelin
2017-09-18 22:25                     ` Jonathan Nieder
2017-09-26 17:05                   ` Jason Cooper
2017-09-26 22:11                     ` Johannes Schindelin
2017-09-26 22:25                       ` [PATCH] technical doc: add a design doc for hash function transition Stefan Beller
2017-09-26 23:38                         ` Jonathan Nieder
2017-09-26 23:51                       ` RFC v3: Another proposed hash function transition plan Jonathan Nieder
2017-10-02 14:54                         ` Jason Cooper
2017-10-02 16:50                           ` Brandon Williams
2017-10-02 14:00                       ` Jason Cooper
2017-10-02 17:18                         ` Linus Torvalds
2017-10-02 19:37                           ` Jeff King
2017-09-13 16:30             ` Jonathan Nieder
2017-09-13 21:52               ` Junio C Hamano
2017-09-13 22:07                 ` Stefan Beller
2017-09-13 22:18                   ` Jonathan Nieder
2017-09-14  2:13                     ` Junio C Hamano
2017-09-14 15:23                       ` Johannes Schindelin
2017-09-14 15:45                         ` demerphq
2017-09-14 22:06                           ` Johannes Schindelin
2017-09-13 22:15                 ` Junio C Hamano
2017-09-13 22:27                   ` Jonathan Nieder [this message]
2017-09-14  2:10                     ` Junio C Hamano
2017-09-14 12:39               ` Johannes Schindelin
2017-09-14 16:36                 ` Brandon Williams
2017-09-14 18:49                 ` Jonathan Nieder
2017-09-15 20:42                   ` Philip Oakley
2017-03-05 11:02 ` RFC: " David Lang
     [not found]   ` <CA+dhYEXHbQfJ6KUB1tWS9u1MLEOJL81fTYkbxu4XO-i+379LPw@mail.gmail.com>
2017-03-06  9:43     ` Jeff King
2017-03-06 23:40   ` Jonathan Nieder
2017-03-07  0:03     ` Mike Hommey
2017-03-06  8:43 ` Jeff King
2017-03-06 18:39   ` Jonathan Tan
2017-03-06 19:22     ` Linus Torvalds
2017-03-06 19:59       ` Brandon Williams
2017-03-06 21:53       ` Junio C Hamano
2017-03-07  8:59     ` Jeff King
2017-03-06 18:43   ` Junio C Hamano
2017-03-07 18:57 ` Ian Jackson
2017-03-07 19:15   ` Linus Torvalds
2017-03-08 11:20     ` Ian Jackson
2017-03-08 15:37       ` Johannes Schindelin
2017-03-08 15:40       ` Johannes Schindelin
2017-03-20  5:21         ` Use base32? Jason Hennessey
2017-03-20  5:58           ` Michael Steuer
2017-03-20  8:05             ` Jacob Keller
2017-03-21  3:07               ` Michael Steuer
2017-03-13  9:24 ` RFC: Another proposed hash function transition plan The Keccak Team
2017-03-13 17:48   ` Jonathan Nieder
2017-03-13 18:34     ` ankostis
2017-03-17 11:07       ` Johannes Schindelin

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