Date: Thu, 23 Feb 2017 13:14:09 -0500
From: Peter Todd <pete@petertodd.org>
To: cryptography@metzdowd.com, bitcoin-dev@lists.linuxfoundation.org
Message-ID: <20170223181409.GA6085@savin.petertodd.org>
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Subject: [bitcoin-dev] SHA1 collisions make Git vulnerable to attakcs by
 third-parties, not just repo maintainers
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Worth noting: the impact of the SHA1 collison attack on Git is *not* limited
only to maintainers making maliciously colliding Git commits, but also
third-party's submitting pull-reqs containing commits, trees, and especially
files for which collisions have been found. This is likely to be exploitabl=
e in
practice with binary files, as reviewers aren't going to necessarily notice
garbage at the end of a file needed for the attack; if the attack can be
extended to constricted character sets like unicode or ASCII, we're in trou=
ble
in general.

Concretely, I could prepare a pair of files with the same SHA1 hash, taking
into account the header that Git prepends when hashing files. I'd then subm=
it
that pull-req to a project with the "clean" version of that file. Once the
maintainer merges my pull-req, possibly PGP signing the git commit, I then =
take
that signature and distribute the same repo, but with the "clean" version
replaced by the malicious version of the file.

--=20
https://petertodd.org 'peter'[:-1]@petertodd.org

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