FWIW, Uncle Timmy considers the non-randomized hashes to be a virtue. It is believed that they give us better-than-random results for commonly encountered datasets. A change to randomized hashes would have a negative performance impact on those cases.
Also, randomizing the hash wreaks havoc on doctests, book examples not matching actual dict reprs, and on efforts by users to optimize the insertion order into dicts with frequent lookups. Raymond On Dec 28, 2011, at 5:28 PM, Michael Foord wrote: > Hello all, > > A paper (well, presentation) has been published highlighting security > problems with the hashing algorithm (exploiting collisions) in many > programming languages Python included: > > > http://events.ccc.de/congress/2011/Fahrplan/attachments/2007_28C3_Effective_DoS_on_web_application_platforms.pdf > > Although it's a security issue I'm posting it here because it is now public > and seems important. > > The issue they report can cause (for example) handling an http post to > consume horrible amounts of cpu. For Python the figures they quoted: > > reasonable-sized attack strings only for 32 bits Plone has max. POST > size of 1 MB > 7 minutes of CPU usage for a 1 MB request > ~20 kbits/s → keep one Core Duo core busy > > This was apparently reported to the security list, but hasn't been responded > to beyond an acknowledgement on November 24th (the original report didn't > make it onto the security list because it was held in a moderation queue). > > The same vulnerability was reported against various languages and web > frameworks, and is already fixed in some of them. > > Their recommended fix is to randomize the hash function. > > All the best, > > Michael > > > -- > http://www.voidspace.org.uk/ > > > May you do good and not evil > May you find forgiveness for yourself and forgive others > May you share freely, never taking more than you give. > -- the sqlite blessing > http://www.sqlite.org/different.html > > > > > > _______________________________________________ > Python-Dev mailing list > Python-Dev@python.org > http://mail.python.org/mailman/listinfo/python-dev > Unsubscribe: > http://mail.python.org/mailman/options/python-dev/raymond.hettinger%40gmail.com _______________________________________________ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
