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Address the concerns of the ``randomness'' of the initial PRNG. Now, we

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use bits from /dev/random to stir the S-box.  Also add an internal counter to
keep the S-box stirred on a regular basis.

Reviewed by: msmith
This commit is contained in:
Dan Moschuk 1999-11-28 23:39:49 +00:00
parent be728db489
commit d65b167028
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=53864
1 changed files with 33 additions and 15 deletions
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48
sys/libkern/arc4random.c
View File

@ -11,12 +11,16 @@
*/
#include <sys/libkern.h>
#include <sys/time.h>
#define ARC4_MAXRUNS 64
static u_int8_t arc4_i, arc4_j;
static int arc4_initialized = 0;
static int arc4_numruns = 0;
static u_int8_t arc4_sbox[256];
extern u_int read_random (void *, u_int);
static __inline void
arc4_swap(u_int8_t *a, u_int8_t *b)
{
@ -27,30 +31,39 @@ arc4_swap(u_int8_t *a, u_int8_t *b)
*b = c;
}
/*
* Stir our S-box.
*/
static void
arc4_randomstir (void)
{
u_int8_t key[256];
int r, n;
r = read_random(key, sizeof(key));
for (n = r; n < sizeof(key); n++)
key[n] = key[n % r];
for (n = 0; n < 256; n++)
{
arc4_j = (arc4_j + arc4_sbox[n] + key[n]) % 256;
arc4_swap(&arc4_sbox[n], &arc4_sbox[arc4_j]);
}
}
/*
* Initialize our S-box to its beginning defaults.
*/
static void
arc4_init(void)
{
struct timespec ts;
u_int8_t key[256];
int n;
for (n = 0; n < 256; n++)
arc4_sbox[n] = (u_int8_t) n;
nanotime(&ts);
srandom(ts.tv_sec ^ ts.tv_nsec);
for (n = 0; n < 256; n++)
key[n] = random() % 256;
arc4_i = arc4_j = 0;
for (n = 0; n < 256; n++)
{
arc4_j = arc4_j + arc4_sbox[n] + key[n];
arc4_swap(&arc4_sbox[n], &arc4_sbox[arc4_j]);
}
arc4_sbox[n] = (u_int8_t) n;
arc4_randomstir();
arc4_initialized = 1;
}
@ -79,6 +92,11 @@ arc4random(void)
/* Initialize array if needed. */
if (!arc4_initialized)
arc4_init();
if (++arc4_numruns > ARC4_MAXRUNS)
{
arc4_randomstir();
arc4_numruns = 0;
}
ret = arc4_randbyte();
ret |= arc4_randbyte() << 8;