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Comparing the sha-1 is much faster than reading the ssd, so it's almost free.

Accidental sha-1 collision is probably not a problem, but in a few years [1] it will be possible to crate sha-1 collisions and use that as an attack. It looks difficult, but supposes that with the correct string an attacker can retrieve the cached information of another user, for example sha1("joedoe:creditcard")=sha1("atacker:hc!?!=u?ee&f%g#jo").

I don't know if they are using randomization, because the collision can be used (in a few years) as a DOS atack [2]

[1] http://www.schneier.com/blog/archives/2012/10/when_will_we_s...

[2] http://www.gossamer-threads.com/lists/python/dev/959026

Your example describes a preimage attack on SHA-1, not a collision attack. Even with a working collision attack you are probably still far away from taking "some.other.input" and creating a sha1("some.other.input") = sha1("johndoe:creditcard").

For instance MD5 collisions are really easy to create but for preimage attacks on MD5 there is still no better approach than just doing brute force.

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