[Python-Dev] Hash collision security issue (now public) (original) (raw)
Alexey Borzenkov snaury at gmail.com
Mon Jan 2 19:57:27 CET 2012
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On Mon, Jan 2, 2012 at 10:53 PM, Alexey Borzenkov <snaury at gmail.com> wrote:
On Mon, Jan 2, 2012 at 7:18 PM, Christian Heimes <lists at cheimes.de> wrote:
Am 02.01.2012 06:55, schrieb Paul McMillan:
I think Ruby uses FNV-1 with a salt, making it less vulnerable to this. FNV is otherwise similar to our existing hash function.
For the record, cryptographically strong hash functions are in the neighborhood of 400% slower than our existing hash function. I've pushed a new patch http://hg.python.org/features/randomhash/rev/0a65d2462e0c It seems for 32-bit version you are using pid for the two constants. Also, it's unclear why you even need to use a random constant for the final pass, you already use random constant as an initial h1, and it should be enough, no need to use for k1. Same for 128-bit: k1, k2, k3, k4 should be initialized to zero, these are key data, they don't need to be mixed with anything.
Sorry, sent too soon. What I mean is that you're initializing a pretty big array of values when you only need a 32-bit value. Pid, in my opinion might be too predictable, it would be a lot better to simply hash pid and gettimeofday bytes to produce this single 32-bit value and use it for h1, h2, h3 and h4 in both 32-bit and 128-bit versions.
Also, I'm not sure how portable is the alwaysinline attribute, is it supported on all compilers and all platforms?
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