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From: Junio C Hamano <gitster@pobox.com>
To: Adam Langley <agl@google.com>
Cc: "Johannes Schindelin" <Johannes.Schindelin@gmx.de>,
	"Ævar Arnfjörð Bjarmason" <avarab@gmail.com>,
	"brian m. carlson" <sandals@crustytoothpaste.net>,
	"Jeff King" <peff@peff.net>, "Mike Hommey" <mh@glandium.org>,
	"Brandon Williams" <bmwill@google.com>,
	"Linus Torvalds" <torvalds@linux-foundation.org>,
	"Jonathan Nieder" <jrnieder@gmail.com>,
	"Git Mailing List" <git@vger.kernel.org>,
	"Stefan Beller" <sbeller@google.com>,
	"Jonathan Tan" <jonathantanmy@google.com>
Subject: Re: Which hash function to use, was Re: RFC: Another proposed hash function transition plan
Date: Fri, 16 Jun 2017 14:12:13 -0700
Message-ID: <xmqqr2yjwsb6.fsf@gitster.mtv.corp.google.com> (raw)
In-Reply-To: <xmqq37azy7ru.fsf@gitster.mtv.corp.google.com> (Junio C. Hamano's message of "Fri, 16 Jun 2017 13:52:53 -0700")

Junio C Hamano <gitster@pobox.com> writes:

> Adam Langley <agl@google.com> writes:
>
>> However, as I'm not a git developer, I've no opinion on whether the
>> cost of carrying implementations of these functions is worth the speed
>> vs using SHA-256, which can be assumed to be supported everywhere
>> already.
>
> Thanks.
>
> My impression from this thread is that even though fast may be
> better than slow, ubiquity trumps it for our use case, as long as
> the thing is not absurdly and unusably slow, of course.  Which makes
> me lean towards something older/more established like SHA-256, and
> it would be a very nice bonus if it gets hardware acceleration more
> widely than others ;-)

Ah, I recall one thing that was mentioned but not discussed much in
the thread: possible use of tree-hashing to exploit multiple cores
hashing a large-ish payload.  As long as it is OK to pick a sound
tree hash coding on top of any (secure) underlying hash function,
I do not think the use of tree-hashing should not affect which exact
underlying hash function is to be used, and I also am not convinced
if we really want tree hashing (some codepaths that deal with a large
payload wants to stream the data in single pass from head to tail)
in the context of Git, but I am not a crypto person, so ...



  reply index

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-03-04  1:12 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 [this message]
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

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