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From: "brian m. carlson" <sandals@crustytoothpaste.net>
To: Adam Langley <agl@google.com>
Cc: "Johannes Schindelin" <Johannes.Schindelin@gmx.de>,
	"Ævar Arnfjörð Bjarmason" <avarab@gmail.com>,
	"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>,
	"Junio Hamano" <gitster@pobox.com>
Subject: Re: Which hash function to use, was Re: RFC: Another proposed hash function transition plan
Date: Thu, 15 Jun 2017 22:41:10 +0000	[thread overview]
Message-ID: <20170615224110.kvrjs3lmwxcoqfaw@genre.crustytoothpaste.net> (raw)
In-Reply-To: <CAL9PXLzhPyE+geUdcLmd=pidT5P8eFEBbSgX_dS88knz2q_LSw@mail.gmail.com>

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On Thu, Jun 15, 2017 at 02:59:57PM -0700, Adam Langley wrote:
> (I was asked to comment a few points in public by Jonathan.)
> 
> I think this group can safely assume that SHA-256, SHA-512, BLAKE2,
> K12, etc are all secure to the extent that I don't believe that making
> comparisons between them on that axis is meaningful. Thus I think the
> question is primarily concerned with performance and implementation
> availability.
> 
> I think any of the above would be reasonable choices. I don't believe
> that length-extension is a concern here.
> 
> SHA-512/256 will be faster than SHA-256 on 64-bit systems in software.
> The graph at https://blake2.net/ suggests a 50% speedup on Skylake. On
> my Ivy Bridge system, it's about 20%.
> 
> (SHA-512/256 does not enjoy the same availability in common libraries however.)
> 
> Both Intel and ARM have SHA-256 instructions defined. I've not seen
> good benchmarks of them yet, but they will make SHA-256 faster than
> SHA-512 when available. However, it's very possible that something
> like BLAKE2bp will still be faster. Of course, BLAKE2bp does not enjoy
> the ubiquity of SHA-256, but nor do you have to wait years for the CPU
> population to advance for high performance.

SHA-256 acceleration exists for some existing Intel platforms already.
However, they're not practically present on anything but servers at the
moment, and so I don't think the acceleration of SHA-256 is a
something we should consider.

The SUPERCOP benchmarks tell me that generally, on 64-bit systems where
acceleration is not available, SHA-256 is the slowest, followed by
SHA3-256.  BLAKE2b is the fastest.

If our goal is performance, then I would argue BLAKE2b-256 is the best
choice.  It is secure and extremely fast.  It does have the benefit that
we get to tell people that by moving away from SHA-1, they will get a
performance boost, pretty much no matter what the system.

BLAKE2bp may be faster, but it introduces additional implementation
complexity.  I'm not sure crypto libraries will implement it, but then
again, OpenSSL only implements BLAKE2b-512 at the moment.  I don't care
much either way, but we should add good tests to exercise the
implementation thoroughly.  We're generally going to need to ship our
own implementation anyway.

I've argued that SHA3-256 probably has the longest life and good
unaccelerated performance, and for that reason, I've preferred it.  But
if AGL says that they're all secure (and I generally think he knows
what he's talking about), we could consider performance more.
-- 
brian m. carlson / brian with sandals: Houston, Texas, US
https://www.crustytoothpaste.net/~bmc | My opinion only
OpenPGP: https://keybase.io/bk2204

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  reply	other threads:[~2017-06-15 22:41 UTC|newest]

Thread overview: 113+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-03-04  1:12 RFC: Another proposed hash function transition plan 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 [this message]
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
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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