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/random"
59 #define THREAD_LOCK() \
62 _pthread_mutex_lock(&arc4random_mtx); \
65 #define THREAD_UNLOCK() \
68 _pthread_mutex_unlock(&arc4random_mtx); \
71 static struct arc4_stream rs;
72 static int rs_initialized;
74 static int arc4_count;
76 static inline u_int8_t arc4_getbyte(void);
77 static void arc4_stir(void);
84 for (n = 0; n < 256; n++)
91 arc4_addrandom(u_char *dat, int datlen)
97 for (n = 0; n < 256; n++) {
100 rs.j = (rs.j + si + dat[n % datlen]);
101 rs.s[rs.i] = rs.s[rs.j];
114 u_int8_t rnd[KEYSIZE];
117 fd = _open(RANDOMDEV, O_RDONLY, 0);
120 if (_read(fd, &rdat, KEYSIZE) == KEYSIZE)
125 (void)gettimeofday(&rdat.tv, NULL);
127 /* We'll just take whatever was on the stack too... */
130 arc4_addrandom((u_char *)&rdat, KEYSIZE);
133 * Throw away the first N bytes of output, as suggested in the
134 * paper "Weaknesses in the Key Scheduling Algorithm of RC4"
135 * by Fluher, Mantin, and Shamir. N=1024 is based on
136 * suggestions in the paper "(Not So) Random Shuffles of RC4"
139 for (n = 0; n < 1024; n++)
140 (void) arc4_getbyte();
141 arc4_count = 1600000;
144 static inline u_int8_t
156 return (rs.s[(si + sj) & 0xff]);
159 static inline u_int32_t
164 val = arc4_getbyte() << 24;
165 val |= arc4_getbyte() << 16;
166 val |= arc4_getbyte() << 8;
167 val |= arc4_getbyte();
173 arc4_check_init(void)
175 if (!rs_initialized) {
182 arc4_check_stir(void)
184 if (!rs_stired || arc4_count <= 0) {
191 arc4random_stir(void)
201 arc4random_addrandom(u_char *dat, int datlen)
206 arc4_addrandom(dat, datlen);
218 rnd = arc4_getword();
226 arc4random_buf(void *_buf, size_t n)
228 u_char *buf = (u_char *)_buf;
234 buf[n] = arc4_getbyte();
241 * Calculate a uniformly distributed random number less than upper_bound
242 * avoiding "modulo bias".
244 * Uniformity is achieved by generating new random numbers until the one
245 * returned is outside the range [0, 2**32 % upper_bound). This
246 * guarantees the selected random number will be inside
247 * [2**32 % upper_bound, 2**32) which maps back to [0, upper_bound)
248 * after reduction modulo upper_bound.
251 arc4random_uniform(u_int32_t upper_bound)
258 #if (ULONG_MAX > 0xffffffffUL)
259 min = 0x100000000UL % upper_bound;
261 /* Calculate (2**32 % upper_bound) avoiding 64-bit math */
262 if (upper_bound > 0x80000000)
263 min = 1 + ~upper_bound; /* 2**32 - upper_bound */
265 /* (2**32 - (x * 2)) % x == 2**32 % x when x <= 2**31 */
266 min = ((0xffffffff - (upper_bound * 2)) + 1) % upper_bound;
271 * This could theoretically loop forever but each retry has
272 * p > 0.5 (worst case, usually far better) of selecting a
273 * number inside the range we need, so it should rarely need
282 return (r % upper_bound);
286 /*-------- Test code for i386 --------*/
288 #include <machine/pctr.h>
290 main(int argc, char **argv)
292 const int iter = 1000000;
297 for (i = 0; i < iter; i++)
302 printf("%qd cycles\n", v);