From: "brian m. carlson" <sandals@crustytoothpaste.net>
To: Johannes Schindelin <Johannes.Schindelin@gmx.de>
Cc: Herczeg Zsolt <zsolt94@gmail.com>, git@vger.kernel.org
Subject: Re: Git and SHA-1 security (again)
Date: Mon, 18 Jul 2016 22:44:50 +0000 [thread overview]
Message-ID: <20160718224450.GF6644@vauxhall.crustytoothpaste.net> (raw)
In-Reply-To: <alpine.DEB.2.20.1607180853300.28832@virtualbox>
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On Mon, Jul 18, 2016 at 09:00:06AM +0200, Johannes Schindelin wrote:
> Hi Brian,
>
> On Sun, 17 Jul 2016, brian m. carlson wrote:
>
> > On Sun, Jul 17, 2016 at 10:01:38AM +0200, Johannes Schindelin wrote:
> > > Out of curiosity: have you considered something like padding the SHA-1s
> > > with, say 0xa1, to the size of the new hash and using that padding to
> > > distinguish between old vs new hash?
> >
> > I'm going to end up having to do something similar because of the issue
> > of submodules. Submodules may still be SHA-1, while the main repo may
> > be a newer hash. I was going to zero-pad, however.
>
> I thought about zero-padding, but there are plenty of
> is_null_sha1()/is_null_oid() calls around. Of course, I assumed
> left-padding. But you may have thought of right-padding instead? That
> would make short name handling much easier, too.
I was going to right-pad.
> FWIW it never crossed my mind to allow different same-sized hash
> algorithms. So I never thought we'd need a way to distinguish, say,
> BLAKE2b-256 from SHA-256.
>
> Is there a good reason to add the maintenance burden of several 256-bit
> hash algorithms, apart from speed (which in my mind should decide which
> one to use, always, rather than letting the user choose)? It would also
> complicate transport even further, let alone subtree merges from
> differently-hashed repositories.
There are really three candidates:
* SHA-256 (the SHA-2 algorithm): While this looks good right now,
cryptanalysis is advancing. This is not a good choice for a long-term
solution.
* SHA3-256 (the SHA-3 algorithm): This is the conservative choice. It's
also faster than SHA-256 on 64-bit systems. It has a very
conservative security margin and is a good long-term choice.
* BLAKE2b-256: This is the blisteringly fast choice. It outperforms
SHA-1 and even MD5 on 64-bit systems. This algorithm was designed so
that nobody would have a reason to use an insecure algorithm. It will
probably be secure for some time, but maybe not as long as SHA3-256.
I'm only considering 256-bit hashes, because anything longer won't fit
on an 80-column terminal in hex form.
The reason I had considered implementing both SHA3-256 and BLAKE2b-256
is that I want there to be no reason not to upgrade. People who need a
FIPS-approved algorithm or want a long-term, conservative choice should
use SHA3-256. People who want even better performance than current Git
would use BLAKE2b-256.
Performance comparison (my implementations):
SHA-1: 437 MiB/s
SHA-256: 196 MiB/s
SHA3-256: 273 MiB/s
BLAKE2b: 649 MiB/s
I hadn't thought about subtree merges, though.
--
brian m. carlson / brian with sandals: Houston, Texas, US
+1 832 623 2791 | https://www.crustytoothpaste.net/~bmc | My opinion only
OpenPGP: https://keybase.io/bk2204
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next prev parent reply other threads:[~2016-07-18 22:45 UTC|newest]
Thread overview: 52+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-07-16 13:48 Git and SHA-1 security (again) Herczeg Zsolt
2016-07-16 20:13 ` brian m. carlson
2016-07-16 21:46 ` Herczeg Zsolt
2016-07-16 22:03 ` brian m. carlson
2016-07-17 8:01 ` Johannes Schindelin
2016-07-17 14:21 ` brian m. carlson
2016-07-17 15:19 ` Duy Nguyen
2016-07-17 15:42 ` brian m. carlson
2016-07-17 16:23 ` Theodore Ts'o
2016-07-17 22:04 ` brian m. carlson
[not found] ` <1468804249.2037.0@smtp.gmail.com>
2016-07-18 1:18 ` Fwd: " Herczeg Zsolt
2016-07-18 7:12 ` Johannes Schindelin
2016-07-18 15:09 ` Herczeg Zsolt
2016-07-18 15:57 ` Johannes Schindelin
2016-07-18 16:05 ` Duy Nguyen
2016-07-19 7:18 ` Johannes Schindelin
2016-07-19 15:31 ` Duy Nguyen
2016-07-19 17:34 ` David Lang
2016-07-19 17:43 ` Duy Nguyen
2016-07-19 17:59 ` David Lang
2016-07-19 18:04 ` Duy Nguyen
2016-07-19 18:58 ` Herczeg Zsolt
2016-07-20 14:48 ` Duy Nguyen
2016-07-20 12:28 ` Johannes Schindelin
2016-07-20 14:44 ` Duy Nguyen
2016-07-20 17:10 ` Stefan Beller
2016-07-20 19:26 ` Junio C Hamano
2016-08-22 22:01 ` Philip Oakley
2016-07-18 16:12 ` Herczeg Zsolt
2016-07-19 7:21 ` Johannes Schindelin
2016-07-18 18:00 ` Junio C Hamano
2016-07-18 21:26 ` Jonathan Nieder
2016-07-18 23:03 ` brian m. carlson
2016-07-21 13:19 ` Johannes Schindelin
2016-07-21 12:53 ` Johannes Schindelin
2016-07-22 15:59 ` Junio C Hamano
2016-07-18 7:00 ` Johannes Schindelin
2016-07-18 22:44 ` brian m. carlson [this message]
2016-07-21 14:13 ` Johannes Schindelin
2016-07-18 16:51 ` Duy Nguyen
2016-07-19 7:31 ` Johannes Schindelin
2016-07-19 7:46 ` David Lang
2016-07-19 16:07 ` Duy Nguyen
2016-07-19 17:06 ` Junio C Hamano
2016-07-19 17:27 ` Duy Nguyen
2016-07-19 18:46 ` Junio C Hamano
2016-07-18 16:51 ` Ævar Arnfjörð Bjarmason
2016-07-18 17:48 ` Herczeg Zsolt
2016-07-18 20:01 ` David Lang
2016-07-18 20:02 ` Ævar Arnfjörð Bjarmason
2016-07-18 20:55 ` Junio C Hamano
2016-07-18 21:28 ` Herczeg Zsolt
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