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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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6
src/util/fairland.c
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@ -179,9 +179,10 @@ main(int argc, char *argv[])
int opt;
char *config_file = NULL;
int i = 0;
int seed_set = 0;
program_name = argv[0];
rnd_seed = time(NULL);
rnd_seed = 0;
while ((opt = getopt(argc, argv, "ae:hioqR:s:v")) != EOF) {
switch (opt) {
@ -202,6 +203,7 @@ main(int argc, char *argv[])
break;
case 'R':
rnd_seed = strtoul(optarg, NULL, 10);
seed_set = 1;
break;
case 's':
outfile = optarg;
@ -219,6 +221,8 @@ main(int argc, char *argv[])
}
parse_args(argc - optind, argv + optind);
if (!seed_set)
rnd_seed = pick_seed();
seed_prng(rnd_seed);
empfile_init();
if (emp_config(config_file) < 0)