>  * it is exceedingly complex Which part exactly? For hash(str), it just add two extra XOR. >  * the method would need to be implemented for all hashable Python types It was already discussed, and it was said that only hash(str) need to be modified. >  * it causes startup time to increase (you need urandom data for >   every single hashable Python data type) My patch reads 8 or 16 bytes from /dev/urandom which doesn't block. Do you have a benchmark showing a difference? I didn't try my patch on Windows yet. >  * it causes run-time to increase due to changes in the hash >   algorithm (more operations in the tight loop) I posted a micro-benchmark on hash(str) on python-dev: the overhead is nul. Did you have numbers showing that the overhead is not nul? >  * causes different processes in a multi-process setup to use different >   hashes for the same object Correct. If you need to get the same hash, you can disable the randomized hash (PYTHONHASHSEED=0) or use a fixed seed (e.g. PYTHONHASHSEED=42). >  * doesn't appear to work well in embedded interpreters that >   regularly restarted interpreters (AFAIK, some objects persist across >   restarts and those will have wrong hash values in the newly started >   instances) test_capi runs _testembed which restarts a embedded interpreters 3 times, and the test pass (with my patch version 5). Can you write a script showing the problem if there is a real problem? In an older version of my patch, the hash secret was recreated at each initiliazation. I changed my patch to only generate the secret once. > The most important issue, though, is that it doesn't really > protect Python against the attack - it only makes it less > likely that an adversary will find the init vector (or a way > around having to find it via crypt analysis). I agree that the patch is not perfect. As written in the patch, it just makes the attack more complex. I consider that it is enough. Perl has a simpler protection than the one proposed in my patch. Is Perl vulnerable to the hash collision vulnerability?