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Fix PRNG seeding to resist guessing

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We seed it with value of time().  It's the traditional way, but it
provides only a few bits of effective entropy when an attacker has a
rough idea when the program started.

Instead, seed with a kernel random number.  If we can't get one, fall
back to a hash of gettimeofday() and getpid().  This should happen
only on old systems or Windows.  Far worse than a kernel random
number, but far better than using time().

Note that fairland used to seed with time() + getpid() until commit
331aac2a (v4.2.20) dropped the getpid(), claiming it didn't improve
the randomness.  Perhaps it didn't under Windows then, but it
certainly did elsewhere, so it was a regression.
This commit is contained in:
Markus Armbruster 2012-12-29 15:06:29 +01:00
parent 39c26f4238
commit 9102ecce54
4 changed files with 68 additions and 2 deletions
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include/chance.h
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@ -39,5 +39,6 @@ extern int roll0(int);
extern int roll(int);
extern int roundavg(double);
extern void seed_prng(unsigned);
extern unsigned pick_seed(void);
#endif