[Python-Dev] RNG in the core (original) (raw)

Christian Heimes lists at cheimes.de
Tue Jan 3 14🔞34 CET 2012

Hello,

all proposed fixes for a randomized hashing function raise and fall with a good random number generator to feed the random seed. The seed must be created very early in the startup phase of the interpreter, preferable before the basic types are initialized. CPython already have multiple sources for random data (win32_urandom in Modules/posixmodule.c, urandom in Lib/os.py, Mersenne twister in Modules/_randommodule.c). However we can't use them because they are wrapped inside Python modules which require infrastructure like initialized base types.

I propose an addition to the current Python C API:

int PyOS_URandom(char *buf, Py_ssize_t len)

Read "len" chars from the OS's RNG into the pre-allocated buffer "buf". The RNG should be suitable for cryptography. In case of an error the function returns -1 and sets an exception, otherwise it returns 0. On Windows I can re-use most of the code of win32_urandom(). For POSIX I have to implement os.urandom() in C in order to read data from /dev/urandom. That's simple and straight forward.

Since some platforms may not have /dev/urandom, we need a PRNG in the core, too. I therefore propose to move the Mersenne twister from randommodule.c into the core, too.

typedef struct { unsigned long state[N]; int index; } _Py_MT_RandomState;

unsigned long _Py_MT_GenRand_Int32(_Py_MT_RandomState *state); // genrand_int32() double _Py_MT_GenRand_Res53(_Py_MT_RandomState *state); // random_random() void _Py_MT_GenRand_Init(_Py_MT_RandomState *state, unsigned long seed); // init_genrand() void _Py_MT_GenRand_InitArray(_Py_MT_RandomState *state, unsigned long init_key[], unsigned long key_length); // init_by_array

I suggest Python/random.c as source file and Python/pyrandom.h as header file. Comments?

Christian

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