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random: Get random seed from /dev/urandom.

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Even though this PRNG is not meant to be cryptographically secure, there is
no reason not to get a high-quality seed.

CC: Stephen Hemminger <shemminger@vyatta.com>
This commit is contained in:
Ben Pfaff
2010-08-12 11:12:13 -07:00
parent e251c8d005
commit 10df718e73
2 changed files with 10 additions and 8 deletions
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17
lib/random.c
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@@ -21,6 +21,7 @@
#include <stdlib.h>
#include <sys/time.h>
#include "entropy.h"
#include "util.h"
/* This is the 32-bit PRNG recommended in G. Marsaglia, "Xorshift RNGs",
@@ -29,7 +30,10 @@
*
* We use this PRNG instead of libc's rand() because rand() varies in quality
* and because its maximum value also varies between 32767 and INT_MAX, whereas
* we often want random numbers in the full range of uint32_t. */
* we often want random numbers in the full range of uint32_t.
*
* This random number generator is intended for purposes that do not require
* cryptographic-quality randomness. */
/* Current random state. */
static uint32_t seed;
@@ -39,19 +43,16 @@ static uint32_t random_next(void);
void
random_init(void)
{
if (!seed) {
while (!seed) {
struct timeval tv;
uint32_t entropy;
if (gettimeofday(&tv, NULL) < 0) {
ovs_fatal(errno, "gettimeofday");
}
get_entropy_or_die(&entropy, 4);
seed = tv.tv_sec ^ tv.tv_usec;
if (!seed) {
/* A 'seed' of 0 is fatal to randomness--the random value will
* always be 0--so use the initial seed mentioned by Marsaglia. */
seed = UINT32_C(2463534242);
}
seed = tv.tv_sec ^ tv.tv_usec ^ entropy;
}
}