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 /* 149 * The sysctl cannot fail. If it does fail on some FreeBSD 150 * derivative or after some future change, just abort so that 151 * the problem will be found and fixed. abort is not normally 152 * suitable for a library but makes sense here. 153 */ 154 abort(); 155 } 156 157 arc4_addrandom(rdat, KEYSIZE); 158 159 /* 160 * Discard early keystream, as per recommendations in: 161 * "(Not So) Random Shuffles of RC4" by Ilya Mironov. 162 */ 163 for (i = 0; i < 3072; i++) 164 (void)arc4_getbyte(); 165 arc4_count = 1600000; 166 } 167 168 static void 169 arc4_stir_if_needed(void) 170 { 171 pid_t pid = getpid(); 172 173 if (arc4_count <= 0 || !rs_initialized || arc4_stir_pid != pid) { 174 arc4_stir_pid = pid; 175 arc4_stir(); 176 } 177 } 178 179 static inline u_int8_t 180 arc4_getbyte(void) 181 { 182 u_int8_t si, sj; 183 184 rs.i = (rs.i + 1); 185 si = rs.s[rs.i]; 186 rs.j = (rs.j + si); 187 sj = rs.s[rs.j]; 188 rs.s[rs.i] = sj; 189 rs.s[rs.j] = si; 190 return (rs.s[(si + sj) & 0xff]); 191 } 192 193 static inline u_int32_t 194 arc4_getword(void) 195 { 196 u_int32_t val; 197 val = arc4_getbyte() << 24; 198 val |= arc4_getbyte() << 16; 199 val |= arc4_getbyte() << 8; 200 val |= arc4_getbyte(); 201 return val; 202 } 203 204 void 205 arc4random_stir(void) 206 { 207 _ARC4_LOCK(); 208 arc4_stir(); 209 _ARC4_UNLOCK(); 210 } 211 212 void 213 arc4random_addrandom(u_char *dat, int datlen) 214 { 215 _ARC4_LOCK(); 216 if (!rs_initialized) 217 arc4_stir(); 218 arc4_addrandom(dat, datlen); 219 _ARC4_UNLOCK(); 220 } 221 222 u_int32_t 223 arc4random(void) 224 { 225 u_int32_t val; 226 _ARC4_LOCK(); 227 arc4_count -= 4; 228 arc4_stir_if_needed(); 229 val = arc4_getword(); 230 _ARC4_UNLOCK(); 231 return val; 232 } 233 234 void 235 arc4random_buf(void *_buf, size_t n) 236 { 237 u_char *buf = (u_char *)_buf; 238 _ARC4_LOCK(); 239 arc4_stir_if_needed(); 240 while (n--) { 241 if (--arc4_count <= 0) 242 arc4_stir(); 243 buf[n] = arc4_getbyte(); 244 } 245 _ARC4_UNLOCK(); 246 } 247 248 /* 249 * Calculate a uniformly distributed random number less than upper_bound 250 * avoiding "modulo bias". 251 * 252 * Uniformity is achieved by generating new random numbers until the one 253 * returned is outside the range [0, 2**32 % upper_bound). This 254 * guarantees the selected random number will be inside 255 * [2**32 % upper_bound, 2**32) which maps back to [0, upper_bound) 256 * after reduction modulo upper_bound. 257 */ 258 u_int32_t 259 arc4random_uniform(u_int32_t upper_bound) 260 { 261 u_int32_t r, min; 262 263 if (upper_bound < 2) 264 return 0; 265 266 /* 2**32 % x == (2**32 - x) % x */ 267 min = -upper_bound % upper_bound; 268 /* 269 * This could theoretically loop forever but each retry has 270 * p > 0.5 (worst case, usually far better) of selecting a 271 * number inside the range we need, so it should rarely need 272 * to re-roll. 273 */ 274 for (;;) { 275 r = arc4random(); 276 if (r >= min) 277 break; 278 } 279 280 return r % upper_bound; 281 } 282 283 #if 0 284 /*-------- Test code for i386 --------*/ 285 #include <stdio.h> 286 #include <machine/pctr.h> 287 int 288 main(int argc, char **argv) 289 { 290 const int iter = 1000000; 291 int i; 292 pctrval v; 293 294 v = rdtsc(); 295 for (i = 0; i < iter; i++) 296 arc4random(); 297 v = rdtsc() - v; 298 v /= iter; 299 300 printf("%qd cycles\n", v); 301 } 302 #endif 303