1 /* $OpenBSD: arc4random.c,v 1.24 2013/06/11 16:59:50 deraadt Exp $ */ 2 3 /* 4 * Copyright (c) 1996, David Mazieres <dm@uun.org> 5 * Copyright (c) 2008, Damien Miller <djm@openbsd.org> 6 * 7 * Permission to use, copy, modify, and distribute this software for any 8 * purpose with or without fee is hereby granted, provided that the above 9 * copyright notice and this permission notice appear in all copies. 10 * 11 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES 12 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF 13 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR 14 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES 15 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN 16 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF 17 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. 18 */ 19 20 /* 21 * Arc4 random number generator for OpenBSD. 22 * 23 * This code is derived from section 17.1 of Applied Cryptography, 24 * second edition, which describes a stream cipher allegedly 25 * compatible with RSA Labs "RC4" cipher (the actual description of 26 * which is a trade secret). The same algorithm is used as a stream 27 * cipher called "arcfour" in Tatu Ylonen's ssh package. 28 * 29 * RC4 is a registered trademark of RSA Laboratories. 30 */ 31 32 #include <sys/cdefs.h> 33 __FBSDID("$FreeBSD$"); 34 35 #include "namespace.h" 36 #include <fcntl.h> 37 #include <limits.h> 38 #include <stdlib.h> 39 #include <unistd.h> 40 #include <sys/param.h> 41 #include <sys/sysctl.h> 42 #include <sys/time.h> 43 #include <pthread.h> 44 45 #include "libc_private.h" 46 #include "un-namespace.h" 47 48 #ifdef __GNUC__ 49 #define inline __inline 50 #else /* !__GNUC__ */ 51 #define inline 52 #endif /* !__GNUC__ */ 53 54 struct arc4_stream { 55 u_int8_t i; 56 u_int8_t j; 57 u_int8_t s[256]; 58 }; 59 60 static pthread_mutex_t arc4random_mtx = PTHREAD_MUTEX_INITIALIZER; 61 62 #define RANDOMDEV "/dev/random" 63 #define KEYSIZE 128 64 #define _ARC4_LOCK() \ 65 do { \ 66 if (__isthreaded) \ 67 _pthread_mutex_lock(&arc4random_mtx); \ 68 } while (0) 69 70 #define _ARC4_UNLOCK() \ 71 do { \ 72 if (__isthreaded) \ 73 _pthread_mutex_unlock(&arc4random_mtx); \ 74 } while (0) 75 76 static int rs_initialized; 77 static struct arc4_stream rs; 78 static pid_t arc4_stir_pid; 79 static int arc4_count; 80 81 extern int __sysctl(int *name, u_int namelen, void *oldp, size_t *oldlenp, 82 void *newp, size_t newlen); 83 84 static inline u_int8_t arc4_getbyte(void); 85 static void arc4_stir(void); 86 87 static inline void 88 arc4_init(void) 89 { 90 int n; 91 92 for (n = 0; n < 256; n++) 93 rs.s[n] = n; 94 rs.i = 0; 95 rs.j = 0; 96 } 97 98 static inline void 99 arc4_addrandom(u_char *dat, int datlen) 100 { 101 int n; 102 u_int8_t si; 103 104 rs.i--; 105 for (n = 0; n < 256; n++) { 106 rs.i = (rs.i + 1); 107 si = rs.s[rs.i]; 108 rs.j = (rs.j + si + dat[n % datlen]); 109 rs.s[rs.i] = rs.s[rs.j]; 110 rs.s[rs.j] = si; 111 } 112 rs.j = rs.i; 113 } 114 115 static size_t 116 arc4_sysctl(u_char *buf, size_t size) 117 { 118 int mib[2]; 119 size_t len, done; 120 121 mib[0] = CTL_KERN; 122 mib[1] = KERN_ARND; 123 done = 0; 124 125 do { 126 len = size; 127 if (__sysctl(mib, 2, buf, &len, NULL, 0) == -1) 128 return (done); 129 done += len; 130 buf += len; 131 size -= len; 132 } while (size > 0); 133 134 return (done); 135 } 136 137 static void 138 arc4_stir(void) 139 { 140 u_char rdat[KEYSIZE]; 141 int i; 142 143 if (!rs_initialized) { 144 arc4_init(); 145 rs_initialized = 1; 146 } 147 if (arc4_sysctl(rdat, KEYSIZE) != KEYSIZE) 148 abort(); /* Random sysctl cannot fail. */ 149 150 arc4_addrandom(rdat, KEYSIZE); 151 152 /* 153 * Discard early keystream, as per recommendations in: 154 * "(Not So) Random Shuffles of RC4" by Ilya Mironov. 155 */ 156 for (i = 0; i < 1024; i++) 157 (void)arc4_getbyte(); 158 arc4_count = 1600000; 159 } 160 161 static void 162 arc4_stir_if_needed(void) 163 { 164 pid_t pid = getpid(); 165 166 if (arc4_count <= 0 || !rs_initialized || arc4_stir_pid != pid) { 167 arc4_stir_pid = pid; 168 arc4_stir(); 169 } 170 } 171 172 static inline u_int8_t 173 arc4_getbyte(void) 174 { 175 u_int8_t si, sj; 176 177 rs.i = (rs.i + 1); 178 si = rs.s[rs.i]; 179 rs.j = (rs.j + si); 180 sj = rs.s[rs.j]; 181 rs.s[rs.i] = sj; 182 rs.s[rs.j] = si; 183 return (rs.s[(si + sj) & 0xff]); 184 } 185 186 static inline u_int32_t 187 arc4_getword(void) 188 { 189 u_int32_t val; 190 val = arc4_getbyte() << 24; 191 val |= arc4_getbyte() << 16; 192 val |= arc4_getbyte() << 8; 193 val |= arc4_getbyte(); 194 return val; 195 } 196 197 void 198 arc4random_stir(void) 199 { 200 _ARC4_LOCK(); 201 arc4_stir(); 202 _ARC4_UNLOCK(); 203 } 204 205 void 206 arc4random_addrandom(u_char *dat, int datlen) 207 { 208 _ARC4_LOCK(); 209 if (!rs_initialized) 210 arc4_stir(); 211 arc4_addrandom(dat, datlen); 212 _ARC4_UNLOCK(); 213 } 214 215 u_int32_t 216 arc4random(void) 217 { 218 u_int32_t val; 219 _ARC4_LOCK(); 220 arc4_count -= 4; 221 arc4_stir_if_needed(); 222 val = arc4_getword(); 223 _ARC4_UNLOCK(); 224 return val; 225 } 226 227 void 228 arc4random_buf(void *_buf, size_t n) 229 { 230 u_char *buf = (u_char *)_buf; 231 _ARC4_LOCK(); 232 arc4_stir_if_needed(); 233 while (n--) { 234 if (--arc4_count <= 0) 235 arc4_stir(); 236 buf[n] = arc4_getbyte(); 237 } 238 _ARC4_UNLOCK(); 239 } 240 241 /* 242 * Calculate a uniformly distributed random number less than upper_bound 243 * avoiding "modulo bias". 244 * 245 * Uniformity is achieved by generating new random numbers until the one 246 * returned is outside the range [0, 2**32 % upper_bound). This 247 * guarantees the selected random number will be inside 248 * [2**32 % upper_bound, 2**32) which maps back to [0, upper_bound) 249 * after reduction modulo upper_bound. 250 */ 251 u_int32_t 252 arc4random_uniform(u_int32_t upper_bound) 253 { 254 u_int32_t r, min; 255 256 if (upper_bound < 2) 257 return 0; 258 259 /* 2**32 % x == (2**32 - x) % x */ 260 min = -upper_bound % upper_bound; 261 /* 262 * This could theoretically loop forever but each retry has 263 * p > 0.5 (worst case, usually far better) of selecting a 264 * number inside the range we need, so it should rarely need 265 * to re-roll. 266 */ 267 for (;;) { 268 r = arc4random(); 269 if (r >= min) 270 break; 271 } 272 273 return r % upper_bound; 274 } 275 276 #if 0 277 /*-------- Test code for i386 --------*/ 278 #include <stdio.h> 279 #include <machine/pctr.h> 280 int 281 main(int argc, char **argv) 282 { 283 const int iter = 1000000; 284 int i; 285 pctrval v; 286 287 v = rdtsc(); 288 for (i = 0; i < iter; i++) 289 arc4random(); 290 v = rdtsc() - v; 291 v /= iter; 292 293 printf("%qd cycles\n", v); 294 } 295 #endif 296