[Python-Dev] Counting collisions for the win

Paul McMillan paul at mcmillan.ws
Sun Jan 22 08:44:24 CET 2012

> I may have a terminology problem here. I expect that a random seed must
> change every time it is used, otherwise the pseudorandom number generator
> using it just returns the same value each time. Should we be talking about a
> salt rather than a seed?

You should read the several other threads, the bug, as well as the
implementation and patch under discussion. Briefly, Python string
hashes are calculated once per string, and then used in many places.
You can't change the hash value for a string during program execution
without breaking everything. The proposed change modifies the starting
value of the hash function to include a process-wide randomly
generated seed. This seed is chosen randomly at runtime, but cannot
change once chosen. Using the seed changes the final output of the
hash to be unpredictable to an attacker, solving the underlying

Salt could also be an appropriate term here, but since salt is
generally changed on a per-use basis (a single process may use many
different salts), seed is more correct, since this value is only
chosen once per process.


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