[Python-Dev] Hash collision security issue (now public)

Victor Stinner victor.stinner at haypocalc.com
Sat Dec 31 03:39:45 CET 2011

> In case the watchdog is not a viable solution as I had assumed it was, I
> think it's more reasonable to indeed consider adding a flag to Python
> that allows randomization of hashes optionally before startup.

A flag will only be needed if the overhead of the fix is too high.

> However as it was said earlier, the attack is a lot more complex to
> carry out on a 64bit environment that it's probably (as it stands right
> now!) safe to ignore.

I suppose that there are still servers running 32 bits Python.

> The main problem there however is not that it's a new attack but that
> some dickheads could now make prebaked attacks against websites to
> disrupt them that might cause some negative publicity.  In general
> though there are so many more ways to DDOS a website than this that I
> would rate the whole issue very low.

There are countermeasures for low level DDOS (ICMP ping flood, TCP syn 
flood, etc.). An application (or a firewall) cannot implement a 
countermeasure for this high level issue. It can only be fixed in Python 
directly (by changing the implementation of the dict type or of the hash 


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