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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>
#include <sys/smp.h>
#include <sys/malloc.h>
#define ARC4_RESEED_BYTES 65536
#define ARC4_RESEED_SECONDS 300
#define ARC4_KEYBYTES 256
int arc4rand_iniseed_state = ARC4_ENTR_NONE;
MALLOC_DEFINE(M_ARC4RANDOM, "arc4random", "arc4random structures");
struct arc4_s {
struct mtx mtx;
u_int8_t i, j;
int numruns;
u_int8_t sbox[256];
time_t t_reseed;
} __aligned(CACHE_LINE_SIZE);
static struct arc4_s *arc4inst = NULL;
#define ARC4_FOREACH(_arc4) \
for (_arc4 = &arc4inst[0]; _arc4 <= &arc4inst[mp_maxid]; _arc4++)
static u_int8_t arc4_randbyte(struct arc4_s *arc4);
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(struct arc4_s* arc4)
{
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 = 768 in our case.)
*
* http://dl.acm.org/citation.cfm?id=646557.694759
*/
for (n = 0; n < 768*4; n++)
arc4_randbyte(arc4);
mtx_unlock(&arc4->mtx);
}
/*
* Initialize our S-box to its beginning defaults.
*/
static void
arc4_init(void)
{
struct arc4_s *arc4;
int n;
arc4inst = malloc((mp_maxid + 1) * sizeof(struct arc4_s),
M_ARC4RANDOM, M_NOWAIT | M_ZERO);
KASSERT(arc4inst != NULL, ("arc4_init: memory allocation error"));
ARC4_FOREACH(arc4) {
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 = -1;
arc4->numruns = 0;
}
}
SYSINIT(arc4, SI_SUB_LOCK, SI_ORDER_ANY, arc4_init, NULL);
static void
arc4_uninit(void)
{
struct arc4_s *arc4;
ARC4_FOREACH(arc4) {
mtx_destroy(&arc4->mtx);
}
free(arc4inst, M_ARC4RANDOM);
}
SYSUNINIT(arc4, SI_SUB_LOCK, SI_ORDER_ANY, arc4_uninit, NULL);
/*
* Generate a random byte.
*/
static u_int8_t
arc4_randbyte(struct arc4_s *arc4)
{
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;
struct arc4_s *arc4;
if (reseed || atomic_cmpset_int(&arc4rand_iniseed_state,
ARC4_ENTR_HAVE, ARC4_ENTR_SEED)) {
ARC4_FOREACH(arc4)
arc4_randomstir(arc4);
}
arc4 = &arc4inst[curcpu];
getmicrouptime(&tv);
if ((arc4->numruns > ARC4_RESEED_BYTES) ||
(tv.tv_sec > arc4->t_reseed))
arc4_randomstir(arc4);
mtx_lock(&arc4->mtx);
arc4->numruns += len;
p = ptr;
while (len--)
*p++ = arc4_randbyte(arc4);
mtx_unlock(&arc4->mtx);
}
uint32_t
arc4random(void)
{
uint32_t ret;
arc4rand(&ret, sizeof ret, 0);
return ret;
}
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