2 * Copyright (c) 1996, David Mazieres <dm@uun.org>
3 * Copyright (c) 2008, Damien Miller <djm@openbsd.org>
5 * Permission to use, copy, modify, and distribute this software for any
6 * purpose with or without fee is hereby granted, provided that the above
7 * copyright notice and this permission notice appear in all copies.
9 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
10 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
11 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
12 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
13 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
14 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
15 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
19 * Arc4 random number generator for OpenBSD.
21 * This code is derived from section 17.1 of Applied Cryptography,
22 * second edition, which describes a stream cipher allegedly
23 * compatible with RSA Labs "RC4" cipher (the actual description of
24 * which is a trade secret). The same algorithm is used as a stream
25 * cipher called "arcfour" in Tatu Ylonen's ssh package.
27 * Here the stream cipher has been modified always to include the time
28 * when initializing the state. That makes it impossible to
29 * regenerate the same random sequence twice, so this can't be used
30 * for encryption, but will generate good random numbers.
32 * RC4 is a registered trademark of RSA Laboratories.
34 * $FreeBSD: src/lib/libc/gen/arc4random.c,v 1.25 2008/09/09 09:46:36 ache Exp $
35 * $DragonFly: src/lib/libc/gen/arc4random.c,v 1.7 2005/11/13 00:07:42 swildner Exp $
38 #include "namespace.h"
39 #include <sys/types.h>
41 #include <sys/sysctl.h>
47 #include "libc_private.h"
48 #include "un-namespace.h"
53 #define RANDOMDEV "/dev/random"
55 #define THREAD_LOCK() \
58 _pthread_mutex_lock(&arc4random_mtx); \
61 #define THREAD_UNLOCK() \
64 _pthread_mutex_unlock(&arc4random_mtx); \
71 u_int8_t s[KEYSIZE * 2];
74 static pthread_mutex_t arc4random_mtx = PTHREAD_MUTEX_INITIALIZER;
76 static struct arc4_stream rs;
77 static int rs_initialized;
79 static int arc4_count;
81 static u_int8_t arc4_getbyte(void);
82 static void arc4_stir(void);
89 for (n = 0; n < KEYSIZE * 2; n++)
96 arc4_addrandom(u_char *dat, size_t datlen)
102 for (n = 0; n < KEYSIZE * 2; n++) {
105 rs.j = (rs.j + si + dat[n % datlen]);
106 rs.s[rs.i] = rs.s[rs.j];
120 u_int8_t rnd[KEYSIZE*2];
125 * NOTE: Don't assume that the garbage on the stack is actually
129 fd = _open(RANDOMDEV, O_RDONLY, 0);
131 n = _read(fd, rnd, sizeof(rnd));
138 * Align for added entropy, sysctl back-off for chroots that might
139 * not have access to /dev/random.
141 n = n & ~15; /* align for added entropy */
142 if (n < sizeof(rnd)) {
143 size_t r = sizeof(rnd) - n;
144 if (sysctlbyname("kern.random", rnd + n, &r, NULL, 0) == 0)
149 * Pray if this code ever gets triggered.
152 if (n <= sizeof(rnd) - sizeof(struct pray)) {
153 struct pray *pray = (void *)(rnd + n);
154 gettimeofday(&pray->tv, NULL);
155 pray->pid = getpid();
156 n += sizeof(struct pray);
158 arc4_addrandom((u_char *)rnd, n);
161 * Throw away the first N bytes of output, as suggested in the
162 * paper "Weaknesses in the Key Scheduling Algorithm of RC4"
163 * by Fluher, Mantin, and Shamir. N=1024 is based on
164 * suggestions in the paper "(Not So) Random Shuffles of RC4"
167 for (n = 0; n < 1024; n++)
171 * Theoretically we can set arc4_count to 1600000. Realistically,
172 * it makes no sense to use a number that high. Use something
190 return (rs.s[(si + sj) & 0xff]);
198 val = arc4_getbyte() << 24;
199 val |= arc4_getbyte() << 16;
200 val |= arc4_getbyte() << 8;
201 val |= arc4_getbyte();
207 arc4_check_init(void)
209 if (!rs_initialized) {
216 arc4_check_stir(void)
218 if (!rs_stired || arc4_count <= 0) {
225 arc4random_stir(void)
235 arc4random_addrandom(uint8_t *dat, size_t datlen)
240 arc4_addrandom(dat, datlen);
252 rnd = arc4_getword();
260 arc4random_buf(void *_buf, size_t n)
262 u_char *buf = (u_char *)_buf;
268 buf[n] = arc4_getbyte();
275 * Calculate a uniformly distributed random number less than upper_bound
276 * avoiding "modulo bias".
278 * Uniformity is achieved by generating new random numbers until the one
279 * returned is outside the range [0, 2**32 % upper_bound). This
280 * guarantees the selected random number will be inside
281 * [2**32 % upper_bound, 2**32) which maps back to [0, upper_bound)
282 * after reduction modulo upper_bound.
285 arc4random_uniform(u_int32_t upper_bound)
292 #if (ULONG_MAX > 0xffffffffUL)
293 min = 0x100000000UL % upper_bound;
295 /* Calculate (2**32 % upper_bound) avoiding 64-bit math */
296 if (upper_bound > 0x80000000)
297 min = 1 + ~upper_bound; /* 2**32 - upper_bound */
299 /* (2**32 - (x * 2)) % x == 2**32 % x when x <= 2**31 */
300 min = ((0xffffffff - (upper_bound * 2)) + 1) % upper_bound;
305 * This could theoretically loop forever but each retry has
306 * p > 0.5 (worst case, usually far better) of selecting a
307 * number inside the range we need, so it should rarely need
316 return (r % upper_bound);
320 /*-------- Test code for i386 --------*/
322 #include <machine/pctr.h>
324 main(int argc, char **argv)
326 const int iter = 1000000;
331 for (i = 0; i < iter; i++)
336 printf("%qd cycles\n", v);