[Python-Dev] Status of the fix for the hash collision vulnerability

Tim Delaney timothy.c.delaney at gmail.com
Tue Jan 17 00:14:02 CET 2012

On 17 January 2012 09:23, Paul McMillan <paul at mcmillan.ws> wrote:

> This is why the "simply throw an error" solution isn't a complete fix.
> Making portions of an interface unusable for regular users is clearly
> a bad thing, and is clearly applicable to other types of poisoned data
> as well. We need to detect collisions and work around them
> transparently.

What if in a pathological collision (e.g. > 1000 collisions), we increased
the size of a dict by a small but random amount? Should be transparent,
have neglible speed penalty, maximal reuse of existing code, and should be
very difficult to attack since the dictionary would change size in a (near)
non-deterministic manner when being attacked (i.e. first attack causes
non-deterministic remap, next attack should fail).

It should also have near-zero effect on existing tests and frameworks since
we would only get the non-deterministic behaviour in pathological cases,
which we would presumably need new tests for.


Tim Delaney
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