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/*-
* THE BEER-WARE LICENSE
*
* <dan@FreeBSD.ORG> wrote this file. As long as you retain this notice you
* can do whatever you want with this stuff. If we meet some day, and you
* think this stuff is worth it, you can buy me a beer in return.
*
* Dan Moschuk
*/
#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");
#include <sys/types.h>
#include <sys/param.h>
#include <sys/kernel.h>
#include <sys/random.h>
#include <sys/libkern.h>
#include <sys/lock.h>
#include <sys/mutex.h>
#include <sys/time.h>
#define ARC4_RESEED_BYTES 65536
#define ARC4_RESEED_SECONDS 300
#define ARC4_KEYBYTES 256
int arc4rand_iniseed_state = ARC4_ENTR_NONE;
static u_int8_t arc4_i, arc4_j;
static int arc4_numruns = 0;
static u_int8_t arc4_sbox[256];
static time_t arc4_t_reseed;
static struct mtx arc4_mtx;
static u_int8_t arc4_randbyte(void);
static __inline void
arc4_swap(u_int8_t *a, u_int8_t *b)
{
u_int8_t c;
c = *a;
*a = *b;
*b = c;
}
/*
* Stir our S-box.
*/
static void
arc4_randomstir(void)
{
u_int8_t key[ARC4_KEYBYTES];
int n;
struct timeval tv_now;
/*
* XXX: FIX!! This isn't brilliant. Need more confidence.
* This returns zero entropy before random(4) is seeded.
*/
(void)read_random(key, ARC4_KEYBYTES);
getmicrouptime(&tv_now);
mtx_lock(&arc4_mtx);
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]);
}
arc4_i = arc4_j = 0;
/* Reset for next reseed cycle. */
arc4_t_reseed = tv_now.tv_sec + ARC4_RESEED_SECONDS;
arc4_numruns = 0;
/*
* Throw away the first N words of output, as suggested in the
* paper "Weaknesses in the Key Scheduling Algorithm of RC4"
* by Fluher, Mantin, and Shamir. (N = 256 in our case.)
*
* http://dl.acm.org/citation.cfm?id=646557.694759
*/
for (n = 0; n < 256*4; n++)
arc4_randbyte();
mtx_unlock(&arc4_mtx);
}
/*
* Initialize our S-box to its beginning defaults.
*/
static void
arc4_init(void)
{
int n;
mtx_init(&arc4_mtx, "arc4_mtx", NULL, MTX_DEF);
arc4_i = arc4_j = 0;
for (n = 0; n < 256; n++)
arc4_sbox[n] = (u_int8_t) n;
arc4_t_reseed = 0;
}
SYSINIT(arc4_init, SI_SUB_LOCK, SI_ORDER_ANY, arc4_init, NULL);
/*
* Generate a random byte.
*/
static u_int8_t
arc4_randbyte(void)
{
u_int8_t arc4_t;
arc4_i = (arc4_i + 1) % 256;
arc4_j = (arc4_j + arc4_sbox[arc4_i]) % 256;
arc4_swap(&arc4_sbox[arc4_i], &arc4_sbox[arc4_j]);
arc4_t = (arc4_sbox[arc4_i] + arc4_sbox[arc4_j]) % 256;
return arc4_sbox[arc4_t];
}
/*
* MPSAFE
*/
void
arc4rand(void *ptr, u_int len, int reseed)
{
u_char *p;
struct timeval tv;
getmicrouptime(&tv);
if (atomic_cmpset_int(&arc4rand_iniseed_state, ARC4_ENTR_HAVE,
ARC4_ENTR_SEED) || reseed ||
(arc4_numruns > ARC4_RESEED_BYTES) ||
(tv.tv_sec > arc4_t_reseed))
arc4_randomstir();
mtx_lock(&arc4_mtx);
arc4_numruns += len;
p = ptr;
while (len--)
*p++ = arc4_randbyte();
mtx_unlock(&arc4_mtx);
}
uint32_t
arc4random(void)
{
uint32_t ret;
arc4rand(&ret, sizeof ret, 0);
return ret;
}
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