[issue13703] Hash collision security issue

[Marc-Andre Lemburg]

Marc-Andre Lemburg <mal at egenix.com> added the comment:

Marc-Andre Lemburg wrote:
> 
> 3. Changing the way strings are hashed doesn't solve the problem.
> 
> Hash values of other types can easily be guessed as well, e.g.
> take integers which use a trivial hash function.

Here's an example for integers on a 64-bit machine:

>>> g = ((x*(2**64 - 1), hash(x*(2**64 - 1))) for x in xrange(1, 1000000))
>>> d = dict(g)

This takes ages to complete and only uses very little memory.
The input data has some 32MB if written down in decimal numbers
- not all that much data either.

32397634

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<http://bugs.python.org/issue13703>
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