Yo Greg! On Wed, 04 Jan 2017 04:19:58 +0000 Greg Rubin <[email protected]> wrote:
> Gary, > > I'll admit that I'm not a python expert by any means, but I'm pretty > certain that the seed is ignored: > http://svn.python.org/projects/python/tags/r30rc1/Lib/random.py > > class SystemRandom(Random): > ... > def seed(self, *args, **kwds): > "Stub method. Not used for a system random number generator." > return None As the man page says, SystemRandom() does not use seed() https://docs.python.org/2/library/random.html "Accordingly, the seed() and jumpahead() methods have no effect and are ignored." > While you're correct that mixing in poor entropy /should/ be safe > (and in this case it is, because it is ignored) NOT ignored. I'll be happy to cite Python source if you want to dig in with me. > that is less often > true for initially provided seeds. There have traditionally been > cases (Java SHA1PRNG, for example) which if initialized with an > explicit seed will use that rather than properly self-seeding with > strong entropy. After the initial seed it would properly mix in even > weak entropy. SystemRandom() calls os.urandom() that calls /dev/urandom. /dev/urandom does not take a seed. The 'seed' is just used later as a mixer, so it is not really a 'seed'. > As far as the argument about the differences between random and > urandom, assuming your aren't generating your long-term keys on a > fresh virtual machine, there should be no practical security > difference between random and urandom. I find this essay does an > excellent job of explaining with urandom is preferable: > http://www.2uo.de/myths-about-urandom/ I'll look at that. Probably a good thing to add some documentation about only running on hosts that already have a lot of entropy. How about we ask the user to add some command line entropy too? Got any good ideas on some other good entropy to stir into the mix? > Finally, modern Linux kernels will use Intel RDRAND as part of the > input into both random and urandom, so either way, you have excellent > entropy mixed in (even on virtualized systems). Oh, do not get me started on RDRAND. RDRAND is commonly thought to be backdoored: http://arstechnica.com/security/2013/12/we-cannot-trust-intel-and-vias-chip-based-crypto-freebsd-developers-say/ > Hope that helps. Yes, you ave given me a nice project. I love paranoid people! RGDS Veritas liberabit vos GARY Quid est veritas? --------------------------------------------------------------------------- Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703 [email protected] Tel:+1 541 382 8588
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