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From: Johannes Schindelin <Johannes.Schindelin@gmx.de>
To: Joan Daemen <jda@noekeon.org>
Cc: Gilles Van Assche <gilles.vanassche@st.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	demerphq <demerphq@gmail.com>,
	Brandon Williams <bmwill@google.com>,
	Junio C Hamano <gitster@pobox.com>,
	Jonathan Nieder <jrnieder@gmail.com>,
	Git Mailing List <git@vger.kernel.org>,
	Stefan Beller <sbeller@google.com>,
	Jonathan Tan <jonathantanmy@google.com>,
	Jeff King <peff@peff.net>, David Lang <david@lang.hm>,
	"brian m. carlson" <sandals@crustytoothpaste.net>,
	Keccak Team <keccak@noekeon.org>
Subject: Re: RFC v3: Another proposed hash function transition plan
Date: Sat, 30 Sep 2017 00:33:33 +0200 (CEST)
Message-ID: <alpine.DEB.2.21.1.1709292355060.40514@virtualbox> (raw)
In-Reply-To: <acd96750-c165-650c-c67f-44465f2075f2@noekeon.org>

Hi Joan,

On Fri, 29 Sep 2017, Joan Daemen wrote:

> if ever there was a SHA-2 competition, it must have been held inside NSA:-)

Oops. My bad, I indeed got confused about that, as you suggest below (I
actually thought of the AES competition, but that was obviously not about
SHA-2). Sorry.

> But maybe you are confusing with the SHA-3 competition. In any case,
> when considering SHA-2 vs SHA-3 for usage in git, you may have a look at
> arguments we give in the following blogpost:
> 
> https://keccak.team/2017/open_source_crypto.html

Thanks for the pointer!

Small nit: the post uses "its" in place of "it's", twice.

It does have a good point, of course: the scientific exchange (which you
call "open-source" in spirit) makes tons of sense.

As far as Git is concerned, we not only care about the source code of the
hash algorithm we use, we need to care even more about what you call
"executable": ready-to-use, high quality, well-tested implementations.

We carry source code for SHA-1 as part of Git's source code, which was
hand-tuned to be as fast as Linus could get it, which was tricky given
that the tuning should be general enough to apply to all common intel
CPUs.

This hand-crafted code was blown out of the water by OpenSSL's SHA-1 in
our tests here at Microsoft, thanks to the fact that OpenSSL does
vectorized SHA-1 computation now.

To me, this illustrates why it is not good enough to have only a reference
implementation available at our finger tips. Of course, above-mentioned
OpenSSL supports SHA-256 and SHA3-256, too, and at least recent versions
vectorize those, too.

Also, ARM processors have become a lot more popular, so we'll want to have
high-quality implementations of the hash algorithm also for those
processors.

Likewise, in contrast to 2005, nowadays implementations of Git in
languages as obscure as Javascript are not only theoretical but do exist
in practice (https://github.com/creationix/js-git). I had a *very* quick
look for libraries providing crypto in Javascript and immediately found
the Standford Javascript Crypto library
(https://github.com/bitwiseshiftleft/sjcl/) which seems to offer SHA-256
but not SHA3-256 computation.

Back to Intel processors: I read some vague hints about extensions
accelerating SHA-256 computation on future Intel processors, but not
SHA3-256.

It would make sense, of course, that more crypto libraries and more
hardware support would be available for SHA-256 than for SHA3-256 given
the time since publication: 16 vs 5 years (I am playing it loose here,
taking just the year into account, not the exact date, so please treat
that merely as a ballpark figure).

So from a practical point of view, I wonder what your take is on, say,
hardware support for SHA3-256. Do you think this will become a focus soon?

Also, what is your take on the question whether SHA-256 is good enough?
SHA-1 was broken theoretically already 10 years after it was published
(which unfortunately did not prevent us from baking it into Git), after
all, while SHA-256 is 16 years old and the only known weakness does not
apply to Git's usage?

Also, while I have the attention of somebody who knows a heck more about
cryptography than Git's top 10 committers combined: how soon do you expect
practical SHA-1 attacks that are much worse than what we already have
seen? I am concerned that if we do not move fast enough to a new hash
algorithm, and somebody finds a way in the meantime to craft arbitrary
messages given a prefix and an SHA-1, then we have a huge problem on
our hands.

Ciao,
Johannes

  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 [this message]
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
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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