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.
35 #include <sys/cdefs.h>
36 __FBSDID("$FreeBSD$");
38 #include "namespace.h"
39 #include <sys/types.h>
46 #include "libc_private.h"
47 #include "un-namespace.h"
55 static pthread_mutex_t arc4random_mtx = PTHREAD_MUTEX_INITIALIZER;
57 #define RANDOMDEV "/dev/urandom"
58 #define THREAD_LOCK() \
61 _pthread_mutex_lock(&arc4random_mtx); \
64 #define THREAD_UNLOCK() \
67 _pthread_mutex_unlock(&arc4random_mtx); \
70 static struct arc4_stream rs;
71 static int rs_initialized;
73 static int arc4_count;
75 static inline u_int8_t arc4_getbyte(void);
76 static void arc4_stir(void);
83 for (n = 0; n < 256; n++)
90 arc4_addrandom(u_char *dat, int datlen)
96 for (n = 0; n < 256; n++) {
99 rs.j = (rs.j + si + dat[n % datlen]);
100 rs.s[rs.i] = rs.s[rs.j];
113 u_int8_t rnd[128 - sizeof(struct timeval) - sizeof(pid_t)];
116 gettimeofday(&rdat.tv, NULL);
118 fd = _open(RANDOMDEV, O_RDONLY, 0);
120 (void) _read(fd, rdat.rnd, sizeof(rdat.rnd));
123 /* fd < 0? Ah, what the heck. We'll just take whatever was on the
126 arc4_addrandom((void *) &rdat, sizeof(rdat));
129 * Throw away the first N bytes of output, as suggested in the
130 * paper "Weaknesses in the Key Scheduling Algorithm of RC4"
131 * by Fluher, Mantin, and Shamir. N=1024 is based on
132 * suggestions in the paper "(Not So) Random Shuffles of RC4"
135 for (n = 0; n < 1024; n++)
136 (void) arc4_getbyte();
137 arc4_count = 1600000;
140 static inline u_int8_t
152 return (rs.s[(si + sj) & 0xff]);
155 static inline u_int32_t
160 val = arc4_getbyte() << 24;
161 val |= arc4_getbyte() << 16;
162 val |= arc4_getbyte() << 8;
163 val |= arc4_getbyte();
169 arc4_check_init(void)
171 if (!rs_initialized) {
178 arc4_check_stir(void)
180 if (!rs_stired || arc4_count <= 0) {
187 arc4random_stir(void)
196 arc4random_addrandom(u_char *dat, int datlen)
201 arc4_addrandom(dat, datlen);
213 rnd = arc4_getword();
221 arc4random_buf(void *_buf, size_t n)
223 u_char *buf = (u_char *)_buf;
229 buf[n] = arc4_getbyte();
236 * Calculate a uniformly distributed random number less than upper_bound
237 * avoiding "modulo bias".
239 * Uniformity is achieved by generating new random numbers until the one
240 * returned is outside the range [0, 2**32 % upper_bound). This
241 * guarantees the selected random number will be inside
242 * [2**32 % upper_bound, 2**32) which maps back to [0, upper_bound)
243 * after reduction modulo upper_bound.
246 arc4random_uniform(u_int32_t upper_bound)
253 #if (ULONG_MAX > 0xffffffffUL)
254 min = 0x100000000UL % upper_bound;
256 /* Calculate (2**32 % upper_bound) avoiding 64-bit math */
257 if (upper_bound > 0x80000000)
258 min = 1 + ~upper_bound; /* 2**32 - upper_bound */
260 /* (2**32 - (x * 2)) % x == 2**32 % x when x <= 2**31 */
261 min = ((0xffffffff - (upper_bound * 2)) + 1) % upper_bound;
266 * This could theoretically loop forever but each retry has
267 * p > 0.5 (worst case, usually far better) of selecting a
268 * number inside the range we need, so it should rarely need
277 return (r % upper_bound);
281 /*-------- Test code for i386 --------*/
283 #include <machine/pctr.h>
285 main(int argc, char **argv)
287 const int iter = 1000000;
292 for (i = 0; i < iter; i++)
297 printf("%qd cycles\n", v);