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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
*
* $FreeBSD$
*/
#include <sys/types.h>
#include <sys/random.h>
#include <sys/libkern.h>
#include <sys/time.h>
#define ARC4_MAXRUNS 16384
#define ARC4_RESEED_SECONDS 300
#define ARC4_KEYBYTES 32 /* 256 bit key */
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];
static struct timeval arc4_tv_nextreseed;
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[256];
int r, n;
/*
* XXX read_random() returns unsafe numbers if the entropy
* device is not loaded -- MarkM.
*/
r = read_random(key, ARC4_KEYBYTES);
/* If r == 0 || -1, just use what was on the stack. */
if (r > 0)
{
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]);
}
/* Reset for next reseed cycle. */
getmicrotime(&arc4_tv_nextreseed);
arc4_tv_nextreseed.tv_sec += ARC4_RESEED_SECONDS;
arc4_numruns = 0;
}
/*
* Initialize our S-box to its beginning defaults.
*/
static void
arc4_init(void)
{
int n;
arc4_i = arc4_j = 0;
for (n = 0; n < 256; n++)
arc4_sbox[n] = (u_int8_t) n;
arc4_randomstir();
arc4_initialized = 1;
/*
* 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.)
*/
for (n = 0; n < 256*4; n++)
arc4_randbyte();
}
/*
* 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];
}
u_int32_t
arc4random(void)
{
u_int32_t ret;
struct timeval tv_now;
/* Initialize array if needed. */
if (!arc4_initialized)
arc4_init();
getmicrotime(&tv_now);
if ((++arc4_numruns > ARC4_MAXRUNS) ||
(tv_now.tv_sec > arc4_tv_nextreseed.tv_sec))
{
arc4_randomstir();
}
ret = arc4_randbyte();
ret |= arc4_randbyte() << 8;
ret |= arc4_randbyte() << 16;
ret |= arc4_randbyte() << 24;
return ret;
}
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