Cryptographic hash uniquness (was [Haskell-cafe] Simple network client)

Richard Kelsall r.kelsall at
Sun May 11 09:15:30 EDT 2008

Graham Klyne wrote:
> This is a very late response ... but I did some calculations as part of 
> some work I did a while ago:
> (See appendix A "The birthday paradox")
> #g

A memorable summary of the birthday paradox being :

There is a 50% chance of a collision when number of digits in your
population size reaches half the number of digits in the largest
possible population.

e.g. With a 128 bit hash you get a 50% chance of a collision when
you've hashed 2^64 files etc.


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