[issue13703] Hash collision security issue

Gregory P. Smith report at bugs.python.org
Mon Feb 6 22:18:22 CET 2012


Gregory P. Smith <greg at krypto.org> added the comment:

>
> > The release managers have pronounced:
> > http://mail.python.org/pipermail/python-dev/2012-January/115892.html
> > Quoting that email:
> >> 1. Simple hash randomization is the way to go. We think this has the
> >> best chance of actually fixing the problem while being fairly
> >> straightforward such that we're comfortable putting it in a stable
> >> release.
> >> 2. It will be off by default in stable releases and enabled by an
> >> envar at runtime. This will prevent code breakage from dictionary
> >> order changing as well as people depending on the hash stability.
>
> Right, but that doesn't contradict what I wrote about adding
> env vars to fix a seed and optionally enable using a random
> seed, or adding collision counting as extra protection for
> cases that are not addressed by the hash seeding, such as
> e.g. collisions caused by 3rd types or numbers.

We won't be back-porting anything more than the hash randomization for
2.6/2.7/3.1/3.2 but we are free to do more in 3.3 if someone can
demonstrate it working well and a need for it.

For me, things like collision counting and tree based collision
buckets when the types are all the same and known comparable make
sense but are really sounding like a lot of additional complexity. I'd
*like* to see active black-box design attack code produced that goes
after something like a wsgi web app written in Python with hash
randomization *enabled* to demonstrate the need before we accept
additional protections like this  for 3.3+.

-gps

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