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random32: seeding improvement 

The rationale is:
   * use u32 consistently
   * no need to do LCG on values from (better) get_random_bytes
   * use more data from get_random_bytes for secondary seeding
   * don't reduce state space on srandom32()
   * enforce state variable initialization restrictions

Note: the second paper has a version of random32() with even longer period
and a version of random64() if needed.

Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Stephen Hemminger 2008-07-30 16:29:19 -07:00 committed by David S. Miller
parent 4adf0af681
commit 697f8d0348
1 changed files with 27 additions and 21 deletions
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48
lib/random32.c
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@ -56,23 +56,12 @@ static u32 __random32(struct rnd_state *state)
return (state->s1 ^ state->s2 ^ state->s3);
}
static void __set_random32(struct rnd_state *state, unsigned long s)
/*
* Handle minimum values for seeds
*/
static inline u32 __seed(u32 x, u32 m)
{
if (s == 0)
s = 1; /* default seed is 1 */
#define LCG(n) (69069 * n)
state->s1 = LCG(s);
state->s2 = LCG(state->s1);
state->s3 = LCG(state->s2);
/* "warm it up" */
__random32(state);
__random32(state);
__random32(state);
__random32(state);
__random32(state);
__random32(state);
return (x < m) ? x + m : x;
}
/**
@ -107,7 +96,7 @@ void srandom32(u32 entropy)
*/
for_each_possible_cpu (i) {
struct rnd_state *state = &per_cpu(net_rand_state, i);
__set_random32(state, state->s1 ^ entropy);
state->s1 = __seed(state->s1 ^ entropy, 1);
}
}
EXPORT_SYMBOL(srandom32);
@ -122,7 +111,19 @@ static int __init random32_init(void)
for_each_possible_cpu(i) {
struct rnd_state *state = &per_cpu(net_rand_state,i);
__set_random32(state, i + jiffies);
#define LCG(x) ((x) * 69069) /* super-duper LCG */
state->s1 = __seed(LCG(i + jiffies), 1);
state->s2 = __seed(LCG(state->s1), 7);
state->s3 = __seed(LCG(state->s2), 15);
/* "warm it up" */
__random32(state);
__random32(state);
__random32(state);
__random32(state);
__random32(state);
__random32(state);
}
return 0;
}
@ -135,13 +136,18 @@ core_initcall(random32_init);
static int __init random32_reseed(void)
{
int i;
unsigned long seed;
for_each_possible_cpu(i) {
struct rnd_state *state = &per_cpu(net_rand_state,i);
u32 seeds[3];
get_random_bytes(&seed, sizeof(seed));
__set_random32(state, seed);
get_random_bytes(&seeds, sizeof(seeds));
state->s1 = __seed(seeds[0], 1);
state->s2 = __seed(seeds[1], 7);
state->s3 = __seed(seeds[2], 15);
/* mix it in */
__random32(state);
}
return 0;
}