From: Eric Sunshine <sunshine@sunshineco.com>
To: "brian m. carlson" <sandals@crustytoothpaste.net>,
Eric Sunshine <sunshine@sunshineco.com>,
Git List <git@vger.kernel.org>,
Jonathan Tan <jonathantanmy@google.com>,
Johannes Schindelin <Johannes.Schindelin@gmx.de>
Subject: Re: [PATCH 00/24] SHA-256 test fixes, part 8
Date: Mon, 13 Jan 2020 18:34:21 -0500 [thread overview]
Message-ID: <CAPig+cTUKc1+L2XOjToCNmip3h1C33-ZhCWMkujptScYy0OeGw@mail.gmail.com> (raw)
In-Reply-To: <20200113231705.GU6570@camp.crustytoothpaste.net>
On Mon, Jan 13, 2020 at 6:17 PM brian m. carlson
<sandals@crustytoothpaste.net> wrote:
> On 2020-01-13 at 13:41:44, Eric Sunshine wrote:
> > The test itself is fine, but it is one of those unfortunate cases of
> > checking for absence of something (which is a wide net). As explained
> > by the commit message[1] of the patch which added the test, the
> > collision occurred only between short OID's. The patch[2] which fixed
> > the problem did so by avoiding short OID's in the scripted
> > implementation of `git rebase -i` (and also flipped the test from
> > `text_expect_failure` to `test_expect_success`).
> >
> > The test, as currently implemented, is very much specific to SHA-1
> > since the FAKE_COMMIT_MESSAGE="collide2 ac4f2ee" it uses only produces
> > a collision with short OID's when SHA-1 is the hashing function, so
> > the prerequisite is correct and serves as documentation (even if it
> > doesn't affect the outcome of the test). Removing that prerequisite
> > should only be done if the test is updated with a different
> > FAKE_COMMIT_MESSAGE which causes a short OID collision when SHA-256 is
> > used.
>
> I'll take another look. When I looked at the output, it looked like
> they didn't collide anymore even under SHA-1, but perhaps I instrumented
> the test wrong and therefore got the wrong result. Thanks for double
> checking.
They might not collide anymore if the length of a short OID has
increased since the test was written[1] (even with the "fix" patch[2]
reverted) since, to fail, the test only needed the common prefix of
the OID's to collide, where the common prefix was the length of the
short OID. So, it's possible that the test doesn't do anything anymore
if the short OID length is now longer. (This might suggest that
dropping the test would be a path forward.)
[1]: 66ae9a57b8 (t3404: rebase -i: demonstrate short SHA-1 collision,
2013-08-23)
[2]: 75c6976655 (rebase -i: fix short SHA-1 collision, 2013-08-23)
next prev parent reply other threads:[~2020-01-13 23:34 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-13 12:38 [PATCH 00/24] SHA-256 test fixes, part 8 brian m. carlson
2020-01-13 12:38 ` [PATCH 01/24] t/lib-pack: support SHA-256 brian m. carlson
2020-01-13 12:38 ` [PATCH 02/24] t3206: make hash size independent brian m. carlson
2020-01-13 12:38 ` [PATCH 03/24] t3305: annotate with SHA1 prerequisite brian m. carlson
2020-01-13 12:38 ` [PATCH 04/24] t3308: make test work with SHA-256 brian m. carlson
2020-01-13 12:38 ` [PATCH 05/24] t3309: " brian m. carlson
2020-01-13 12:38 ` [PATCH 06/24] t3310: " brian m. carlson
2020-01-13 12:38 ` [PATCH 07/24] t3311: " brian m. carlson
2020-01-13 12:38 ` [PATCH 08/24] t3404: remove SHA1 prerequisite brian m. carlson
2020-01-13 12:38 ` [PATCH 09/24] t4013: make test hash independent brian m. carlson
2020-01-13 12:38 ` [PATCH 10/24] t4060: make test work with SHA-256 brian m. carlson
2020-01-13 12:38 ` [PATCH 11/24] t4211: make test hash independent brian m. carlson
2020-01-13 12:38 ` [PATCH 12/24] t5302: make hash size independent brian m. carlson
2020-01-13 12:38 ` [PATCH 13/24] t5309: make test hash independent brian m. carlson
2020-01-13 12:38 ` [PATCH 14/24] t5313: " brian m. carlson
2020-01-13 12:38 ` [PATCH 15/24] t5321: " brian m. carlson
2020-01-13 12:38 ` [PATCH 16/24] t5515: " brian m. carlson
2020-01-13 12:38 ` [PATCH 17/24] t5318: update for SHA-256 brian m. carlson
2020-01-13 13:50 ` Eric Sunshine
2020-01-13 23:14 ` brian m. carlson
2020-01-13 12:38 ` [PATCH 18/24] t5616: use correct filter syntax brian m. carlson
2020-01-13 20:28 ` [PATCH] t5616: make robust to delta base change Jonathan Tan
2020-01-13 23:11 ` brian m. carlson
2020-01-25 22:43 ` brian m. carlson
2020-01-13 12:38 ` [PATCH 19/24] t5607: make hash size independent brian m. carlson
2020-01-13 12:38 ` [PATCH 20/24] t5703: make test work with SHA-256 brian m. carlson
2020-01-13 13:53 ` Eric Sunshine
2020-01-13 23:15 ` brian m. carlson
2020-01-13 12:38 ` [PATCH 21/24] t5703: switch tests to use test_oid brian m. carlson
2020-01-13 12:38 ` [PATCH 22/24] t6000: abstract away SHA-1-specific constants brian m. carlson
2020-01-13 12:38 ` [PATCH 23/24] t6006: make hash size independent brian m. carlson
2020-01-13 12:38 ` [PATCH 24/24] t6024: update for SHA-256 brian m. carlson
2020-01-13 13:41 ` [PATCH 00/24] SHA-256 test fixes, part 8 Eric Sunshine
2020-01-13 23:17 ` brian m. carlson
2020-01-13 23:34 ` Eric Sunshine [this message]
2020-01-16 0:28 ` Johannes Schindelin
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