Marc-Andre Lemburg added the comment: On 13.05.2014 11:06, Antoine Pitrou wrote: > > Is ~/.rnd any kind of serious? It hasn't been modified since two weeks on my > system (which is rebooted every day).
The file is apparently only updated if you use one the OpenSSL commands which needs random data. grep for "RAND_write_file" in the apps/ subdir of the OpenSSL distribution. Of course, applications can also use that API, so there may be other situations where it gets updated as well. However, when removing that file, OpenSSL still only reads 32 bytes from /dev/urandom, which suggests that it's either using some other sources of randomness as well (there are some timing tricks being used in the code for this), or (more likely) simply doesn't need more random bytes to start with. So while the file does have some meaning, it's not why I had thought it would be. Here's a more likely explanation: The OpenSSL random number source only works with hash function feedback and random data that gets added to it. It's not an PRNG with provable characteristics. OpenSSL uses SHA-1 for hashing which has a 20 byte digest size, so an initial vector of 32 bytes is a good start (though more are always better ;-)): http://en.wikipedia.org/wiki/Randomness_extractor That said and coming back to the question why 32 bytes are enough for OpenSSL: the OpenSSL RNG is being seeded with a seed from the full range of possible values (160 bits). It's period is a lot smaller than the MT one (19937 bits), which is why fewer random bytes are needed. ---------- _______________________________________ Python tracker <rep...@bugs.python.org> <http://bugs.python.org/issue21470> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
