[Python-Dev] Hash collision security issue (now public)
solipsis at pitrou.net
Fri Jan 6 01:59:10 CET 2012
On Fri, 06 Jan 2012 01:50:00 +0100
Christian Heimes <lists at cheimes.de> wrote:
> Am 06.01.2012 01:34, schrieb Nick Coghlan:
> > On Fri, Jan 6, 2012 at 10:07 AM, Steven D'Aprano <steve at pearwood.info> wrote:
> >> Surely the way to verify the behaviour is to run this from the shell:
> >> python -c print(hash("abcde"))
> >> twice, and see that the calls return different values. (Or have I
> >> misunderstood the way the fix is going to work?)
> >> In any case, I wouldn't want to rely on the presence of a flag in the sys
> >> module to verify the behaviour, I'd want to see for myself that hash
> >> collisions are no longer predictable.
> > More directly, you can just check that the hash of the empty string is non-zero.
> > So -1 for a flag in the sys module - "hash('') != 0" should serve as a
> > sufficient check whether or not process-level string hash
> > randomisation is in effect.
> This might not work as we have to special case empty strings and perhaps
> \0 strings, too.
The special case value doesn't have to be zero. Make it age(Barry) for
example (which, I think, is still representable in a 32-bit integer!).
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