[issue13703] Hash collision security issue

[Christian Heimes]

Christian Heimes <lists at cheimes.de> added the comment:

Victor, please ignore my code related to hash randomization for now. I've deliberately not linked my branch to this bug report. I'm well aware that it's not secure and that it's pretty easy to reverse engineer the seed from a hash of a short string. The code is a proof of concept to detect failing tests and other issues.

I'm in private contact with Paul and we are working together. He has done extended research and I'll gladly follow his expertise. I've already discussed the issue with small strings, but I can't recall if it was a private mail to Paul or a public one to the dev list.

Paul:
I still think that you should special case short strings (five or few chars sound good). An attacker can't do much harm with one to five char strings but such short strings may make it too easy to calculate the seed.

16kb of seed is still a lot. Most CPUs have about 16 to 32, maybe 64kb L1 cache for data. 1024 to 4096 bytes should increase cache locality and reduce speed impacts.

PS: I'm going to reply to your last mail tomorrow.

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