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Re: Optional/compressed text bases

From: Peter Samuelson <peter_at_p12n.org>
Date: 2006-05-11 20:06:09 CEST

> I wish I could remember the link, but I read about using the MD5 of
> the file forward and then the MD5 of the file backwards, producing 2
> MD5 values and that along with the size of the data produced a chance
> of collision so small to be (almost) impossible. Subversion could
> also add modify time to increase this even more.

The chance of MD5 collisions is already so small to be (almost)
impossible. The hash is 128 bits long, so you only have to start to
worry when the number of files starts to approach 2^64, or
18000000000000000000. So 128-bit MD5 is already overkill, never mind
your proposed 256-bit variant.

Collisions can be produced _on purpose_, with a lot of CPU power. But
that requires access to the repository or working copy, which means the
adversary is already trusted and you have already lost.

Received on Thu May 11 20:06:44 2006

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