SHA1 collisions proven possisble

Richard Hesse richard.hesse at
Sat Feb 25 17:26:28 UTC 2017

Git prefixes blobs with its own data. You're not going to break git with a
SHA-1 binary collision. However, svn is very vulnerable to breaking.

On Thu, Feb 23, 2017 at 3:11 PM, J. Hellenthal <jhellenthal at>

> It's actually pretty serious in Git and the banking markets where there is
> high usage of sha1. Considering the wide adoption of Git, this is a pretty
> serious issue that will only become worse ten-fold over the years. Visible
> abuse will not be near as widely seen as the initial shattering but
> escalate over much longer periods.
> Take it serious ? Why wouldn't you !?
> --
>  Onward!,
>  Jason Hellenthal,
>  Systems & Network Admin,
>  Mobile: 0x9CA0BD58,
> On Feb 23, 2017, at 16:40, Ricky Beam <jfbeam at> wrote:
> > On Thu, 23 Feb 2017 15:03:34 -0500, Patrick W. Gilmore <
> patrick at> wrote:
> > More seriously: The attack (or at least as much as we can glean from the
> blog post) cannot find a collision (file with same hash) from an arbitrary
> file. The attack creates two files which have the same hash, which is
> scary, but not as bad as it could be.
> Exactly. This is just more sky-is-falling nonsense. Of course collisions
> exist. They occur in every hash function. It's only marginally noteworthy
> when someone finds a collision. It's neat the Google has found a way to
> generate a pair of files with the same hash -- at colossal computational
> cost! However this in no way invalidates SHA-1 or documents signed by
> SHA-1. You still cannot take an existing document, modify it in a
> meaningful way, and keep the same hash.
> [Nor can you generate a blob to match an arbitrary hash (which would be
> death of all bittorrent)]

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