[issue13703] Hash collision security issue

[STINNER Victor]

STINNER Victor <victor.stinner at haypocalc.com> added the comment:

Work-in-progress patch implementing my randomized hash function (random.patch):
 - add PyOS_URandom() using CryptoGen, SSL (only on VMS!!) or /dev/urandom, will a fallback on a dummy LCG if the OS urandom failed
 - posix.urandom() is always defined and reuses PyOS_URandom()
 - hash(str) is now randomized using two random Py_hash_t values: don't touch the critical loop, only add a prefix and a suffix

Notes:
 - PyOS_URandom() reuses mostly code from Modules/posixmodule.c, except dev_urandom() and fallback_urandom() which are new
 - I removed memset(PyBytes_AS_STRING(result), 0, howMany); from win32_urandom() because it doesn't really change anything because the LCG is used if win32_urandom() fails
 - Python refuses to start if the OS urandom is missing.
 - Python/random.c code may be moved into Python/pythonrun.c if it is an issue to add a new file in old Python versions.
 - If the OS urandom fails to generate the unicode hash secret, no warning is emitted (because the LCG is used). I don't know if a warning is needed in this case.
 - os.urandom() argument is now a Py_ssize_t instead of an int

TODO:
 - add an environment option to ignore the OS urandom and only uses the LCG
 - fix all tests broken because of the randomized hash(str)
 - PyOS_URandom() raises exceptions whereas it is called before creating the interpreter state. I suppose that it cannot work like this.
 - review and test PyOS_URandom()
 - review and test the new randomized hash(str)

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keywords: +patch
Added file: http://bugs.python.org/file24142/random.patch

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