1 /* $NetBSD: arc4random.c,v 1.1.1.1 2013/12/27 23:31:19 christos Exp $ */ 2 3 /* Portable arc4random.c based on arc4random.c from OpenBSD. 4 * Portable version by Chris Davis, adapted for Libevent by Nick Mathewson 5 * Copyright (c) 2010 Chris Davis, Niels Provos, and Nick Mathewson 6 * Copyright (c) 2010-2012 Niels Provos and Nick Mathewson 7 * 8 * Note that in Libevent, this file isn't compiled directly. Instead, 9 * it's included from evutil_rand.c 10 */ 11 12 /* 13 * Copyright (c) 1996, David Mazieres <dm@uun.org> 14 * Copyright (c) 2008, Damien Miller <djm@openbsd.org> 15 * 16 * Permission to use, copy, modify, and distribute this software for any 17 * purpose with or without fee is hereby granted, provided that the above 18 * copyright notice and this permission notice appear in all copies. 19 * 20 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES 21 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF 22 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR 23 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES 24 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN 25 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF 26 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. 27 */ 28 29 /* 30 * Arc4 random number generator for OpenBSD. 31 * 32 * This code is derived from section 17.1 of Applied Cryptography, 33 * second edition, which describes a stream cipher allegedly 34 * compatible with RSA Labs "RC4" cipher (the actual description of 35 * which is a trade secret). The same algorithm is used as a stream 36 * cipher called "arcfour" in Tatu Ylonen's ssh package. 37 * 38 * Here the stream cipher has been modified always to include the time 39 * when initializing the state. That makes it impossible to 40 * regenerate the same random sequence twice, so this can't be used 41 * for encryption, but will generate good random numbers. 42 * 43 * RC4 is a registered trademark of RSA Laboratories. 44 */ 45 46 #ifndef ARC4RANDOM_EXPORT 47 #define ARC4RANDOM_EXPORT 48 #endif 49 50 #ifndef ARC4RANDOM_UINT32 51 #define ARC4RANDOM_UINT32 uint32_t 52 #endif 53 54 #ifndef ARC4RANDOM_NO_INCLUDES 55 #include "evconfig-private.h" 56 #ifdef _WIN32 57 #include <wincrypt.h> 58 #include <process.h> 59 #else 60 #include <fcntl.h> 61 #include <unistd.h> 62 #include <sys/param.h> 63 #include <sys/time.h> 64 #ifdef EVENT__HAVE_SYS_SYSCTL_H 65 #include <sys/sysctl.h> 66 #endif 67 #endif 68 #include <limits.h> 69 #include <stdlib.h> 70 #include <string.h> 71 #endif 72 73 /* Add platform entropy 32 bytes (256 bits) at a time. */ 74 #define ADD_ENTROPY 32 75 76 /* Re-seed from the platform RNG after generating this many bytes. */ 77 #define BYTES_BEFORE_RESEED 1600000 78 79 struct arc4_stream { 80 unsigned char i; 81 unsigned char j; 82 unsigned char s[256]; 83 }; 84 85 #ifdef _WIN32 86 #define getpid _getpid 87 #define pid_t int 88 #endif 89 90 static int rs_initialized; 91 static struct arc4_stream rs; 92 static pid_t arc4_stir_pid; 93 static int arc4_count; 94 static int arc4_seeded_ok; 95 96 static inline unsigned char arc4_getbyte(void); 97 98 static inline void 99 arc4_init(void) 100 { 101 int n; 102 103 for (n = 0; n < 256; n++) 104 rs.s[n] = n; 105 rs.i = 0; 106 rs.j = 0; 107 } 108 109 static inline void 110 arc4_addrandom(const unsigned char *dat, int datlen) 111 { 112 int n; 113 unsigned char si; 114 115 rs.i--; 116 for (n = 0; n < 256; n++) { 117 rs.i = (rs.i + 1); 118 si = rs.s[rs.i]; 119 rs.j = (rs.j + si + dat[n % datlen]); 120 rs.s[rs.i] = rs.s[rs.j]; 121 rs.s[rs.j] = si; 122 } 123 rs.j = rs.i; 124 } 125 126 #ifndef _WIN32 127 static ssize_t 128 read_all(int fd, unsigned char *buf, size_t count) 129 { 130 size_t numread = 0; 131 ssize_t result; 132 133 while (numread < count) { 134 result = read(fd, buf+numread, count-numread); 135 if (result<0) 136 return -1; 137 else if (result == 0) 138 break; 139 numread += result; 140 } 141 142 return (ssize_t)numread; 143 } 144 #endif 145 146 #ifdef _WIN32 147 #define TRY_SEED_WIN32 148 static int 149 arc4_seed_win32(void) 150 { 151 /* This is adapted from Tor's crypto_seed_rng() */ 152 static int provider_set = 0; 153 static HCRYPTPROV provider; 154 unsigned char buf[ADD_ENTROPY]; 155 156 if (!provider_set) { 157 if (!CryptAcquireContext(&provider, NULL, NULL, PROV_RSA_FULL, 158 CRYPT_VERIFYCONTEXT)) { 159 if (GetLastError() != (DWORD)NTE_BAD_KEYSET) 160 return -1; 161 } 162 provider_set = 1; 163 } 164 if (!CryptGenRandom(provider, sizeof(buf), buf)) 165 return -1; 166 arc4_addrandom(buf, sizeof(buf)); 167 memset(buf, 0, sizeof(buf)); 168 arc4_seeded_ok = 1; 169 return 0; 170 } 171 #endif 172 173 #if defined(EVENT__HAVE_SYS_SYSCTL_H) && defined(EVENT__HAVE_SYSCTL) 174 #if EVENT__HAVE_DECL_CTL_KERN && EVENT__HAVE_DECL_KERN_RANDOM && EVENT__HAVE_DECL_RANDOM_UUID 175 #define TRY_SEED_SYSCTL_LINUX 176 static int 177 arc4_seed_sysctl_linux(void) 178 { 179 /* Based on code by William Ahern, this function tries to use the 180 * RANDOM_UUID sysctl to get entropy from the kernel. This can work 181 * even if /dev/urandom is inaccessible for some reason (e.g., we're 182 * running in a chroot). */ 183 int mib[] = { CTL_KERN, KERN_RANDOM, RANDOM_UUID }; 184 unsigned char buf[ADD_ENTROPY]; 185 size_t len, n; 186 unsigned i; 187 int any_set; 188 189 memset(buf, 0, sizeof(buf)); 190 191 for (len = 0; len < sizeof(buf); len += n) { 192 n = sizeof(buf) - len; 193 194 if (0 != sysctl(mib, 3, &buf[len], &n, NULL, 0)) 195 return -1; 196 } 197 /* make sure that the buffer actually got set. */ 198 for (i=0,any_set=0; i<sizeof(buf); ++i) { 199 any_set |= buf[i]; 200 } 201 if (!any_set) 202 return -1; 203 204 arc4_addrandom(buf, sizeof(buf)); 205 memset(buf, 0, sizeof(buf)); 206 arc4_seeded_ok = 1; 207 return 0; 208 } 209 #endif 210 211 #if EVENT__HAVE_DECL_CTL_KERN && EVENT__HAVE_DECL_KERN_ARND 212 #define TRY_SEED_SYSCTL_BSD 213 static int 214 arc4_seed_sysctl_bsd(void) 215 { 216 /* Based on code from William Ahern and from OpenBSD, this function 217 * tries to use the KERN_ARND syscall to get entropy from the kernel. 218 * This can work even if /dev/urandom is inaccessible for some reason 219 * (e.g., we're running in a chroot). */ 220 int mib[] = { CTL_KERN, KERN_ARND }; 221 unsigned char buf[ADD_ENTROPY]; 222 size_t len, n; 223 int i, any_set; 224 225 memset(buf, 0, sizeof(buf)); 226 227 len = sizeof(buf); 228 if (sysctl(mib, 2, buf, &len, NULL, 0) == -1) { 229 for (len = 0; len < sizeof(buf); len += sizeof(unsigned)) { 230 n = sizeof(unsigned); 231 if (n + len > sizeof(buf)) 232 n = len - sizeof(buf); 233 if (sysctl(mib, 2, &buf[len], &n, NULL, 0) == -1) 234 return -1; 235 } 236 } 237 /* make sure that the buffer actually got set. */ 238 for (i=any_set=0; i<sizeof(buf); ++i) { 239 any_set |= buf[i]; 240 } 241 if (!any_set) 242 return -1; 243 244 arc4_addrandom(buf, sizeof(buf)); 245 memset(buf, 0, sizeof(buf)); 246 arc4_seeded_ok = 1; 247 return 0; 248 } 249 #endif 250 #endif /* defined(EVENT__HAVE_SYS_SYSCTL_H) */ 251 252 #ifdef __linux__ 253 #define TRY_SEED_PROC_SYS_KERNEL_RANDOM_UUID 254 static int 255 arc4_seed_proc_sys_kernel_random_uuid(void) 256 { 257 /* Occasionally, somebody will make /proc/sys accessible in a chroot, 258 * but not /dev/urandom. Let's try /proc/sys/kernel/random/uuid. 259 * Its format is stupid, so we need to decode it from hex. 260 */ 261 int fd; 262 char buf[128]; 263 unsigned char entropy[64]; 264 int bytes, n, i, nybbles; 265 for (bytes = 0; bytes<ADD_ENTROPY; ) { 266 fd = evutil_open_closeonexec_("/proc/sys/kernel/random/uuid", O_RDONLY, 0); 267 if (fd < 0) 268 return -1; 269 n = read(fd, buf, sizeof(buf)); 270 close(fd); 271 if (n<=0) 272 return -1; 273 memset(entropy, 0, sizeof(entropy)); 274 for (i=nybbles=0; i<n; ++i) { 275 if (EVUTIL_ISXDIGIT_(buf[i])) { 276 int nyb = evutil_hex_char_to_int_(buf[i]); 277 if (nybbles & 1) { 278 entropy[nybbles/2] |= nyb; 279 } else { 280 entropy[nybbles/2] |= nyb<<4; 281 } 282 ++nybbles; 283 } 284 } 285 if (nybbles < 2) 286 return -1; 287 arc4_addrandom(entropy, nybbles/2); 288 bytes += nybbles/2; 289 } 290 memset(entropy, 0, sizeof(entropy)); 291 memset(buf, 0, sizeof(buf)); 292 return 0; 293 } 294 #endif 295 296 #ifndef _WIN32 297 #define TRY_SEED_URANDOM 298 static int 299 arc4_seed_urandom(void) 300 { 301 /* This is adapted from Tor's crypto_seed_rng() */ 302 static const char *filenames[] = { 303 "/dev/srandom", "/dev/urandom", "/dev/random", NULL 304 }; 305 unsigned char buf[ADD_ENTROPY]; 306 int fd, i; 307 size_t n; 308 309 for (i = 0; filenames[i]; ++i) { 310 fd = evutil_open_closeonexec_(filenames[i], O_RDONLY, 0); 311 if (fd<0) 312 continue; 313 n = read_all(fd, buf, sizeof(buf)); 314 close(fd); 315 if (n != sizeof(buf)) 316 return -1; 317 arc4_addrandom(buf, sizeof(buf)); 318 memset(buf, 0, sizeof(buf)); 319 arc4_seeded_ok = 1; 320 return 0; 321 } 322 323 return -1; 324 } 325 #endif 326 327 static int 328 arc4_seed(void) 329 { 330 int ok = 0; 331 /* We try every method that might work, and don't give up even if one 332 * does seem to work. There's no real harm in over-seeding, and if 333 * one of these sources turns out to be broken, that would be bad. */ 334 #ifdef TRY_SEED_WIN32 335 if (0 == arc4_seed_win32()) 336 ok = 1; 337 #endif 338 #ifdef TRY_SEED_URANDOM 339 if (0 == arc4_seed_urandom()) 340 ok = 1; 341 #endif 342 #ifdef TRY_SEED_PROC_SYS_KERNEL_RANDOM_UUID 343 if (0 == arc4_seed_proc_sys_kernel_random_uuid()) 344 ok = 1; 345 #endif 346 #ifdef TRY_SEED_SYSCTL_LINUX 347 /* Apparently Linux is deprecating sysctl, and spewing warning 348 * messages when you try to use it. */ 349 if (!ok && 0 == arc4_seed_sysctl_linux()) 350 ok = 1; 351 #endif 352 #ifdef TRY_SEED_SYSCTL_BSD 353 if (0 == arc4_seed_sysctl_bsd()) 354 ok = 1; 355 #endif 356 return ok ? 0 : -1; 357 } 358 359 static int 360 arc4_stir(void) 361 { 362 int i; 363 364 if (!rs_initialized) { 365 arc4_init(); 366 rs_initialized = 1; 367 } 368 369 arc4_seed(); 370 if (!arc4_seeded_ok) 371 return -1; 372 373 /* 374 * Discard early keystream, as per recommendations in 375 * "Weaknesses in the Key Scheduling Algorithm of RC4" by 376 * Scott Fluhrer, Itsik Mantin, and Adi Shamir. 377 * http://www.wisdom.weizmann.ac.il/~itsik/RC4/Papers/Rc4_ksa.ps 378 * 379 * Ilya Mironov's "(Not So) Random Shuffles of RC4" suggests that 380 * we drop at least 2*256 bytes, with 12*256 as a conservative 381 * value. 382 * 383 * RFC4345 says to drop 6*256. 384 * 385 * At least some versions of this code drop 4*256, in a mistaken 386 * belief that "words" in the Fluhrer/Mantin/Shamir paper refers 387 * to processor words. 388 * 389 * We add another sect to the cargo cult, and choose 12*256. 390 */ 391 for (i = 0; i < 12*256; i++) 392 (void)arc4_getbyte(); 393 arc4_count = BYTES_BEFORE_RESEED; 394 395 return 0; 396 } 397 398 399 static void 400 arc4_stir_if_needed(void) 401 { 402 pid_t pid = getpid(); 403 404 if (arc4_count <= 0 || !rs_initialized || arc4_stir_pid != pid) 405 { 406 arc4_stir_pid = pid; 407 arc4_stir(); 408 } 409 } 410 411 static inline unsigned char 412 arc4_getbyte(void) 413 { 414 unsigned char si, sj; 415 416 rs.i = (rs.i + 1); 417 si = rs.s[rs.i]; 418 rs.j = (rs.j + si); 419 sj = rs.s[rs.j]; 420 rs.s[rs.i] = sj; 421 rs.s[rs.j] = si; 422 return (rs.s[(si + sj) & 0xff]); 423 } 424 425 static inline unsigned int 426 arc4_getword(void) 427 { 428 unsigned int val; 429 430 val = arc4_getbyte() << 24; 431 val |= arc4_getbyte() << 16; 432 val |= arc4_getbyte() << 8; 433 val |= arc4_getbyte(); 434 435 return val; 436 } 437 438 #ifndef ARC4RANDOM_NOSTIR 439 ARC4RANDOM_EXPORT int 440 arc4random_stir(void) 441 { 442 int val; 443 ARC4_LOCK_(); 444 val = arc4_stir(); 445 ARC4_UNLOCK_(); 446 return val; 447 } 448 #endif 449 450 #ifndef ARC4RANDOM_NOADDRANDOM 451 ARC4RANDOM_EXPORT void 452 arc4random_addrandom(const unsigned char *dat, int datlen) 453 { 454 int j; 455 ARC4_LOCK_(); 456 if (!rs_initialized) 457 arc4_stir(); 458 for (j = 0; j < datlen; j += 256) { 459 /* arc4_addrandom() ignores all but the first 256 bytes of 460 * its input. We want to make sure to look at ALL the 461 * data in 'dat', just in case the user is doing something 462 * crazy like passing us all the files in /var/log. */ 463 arc4_addrandom(dat + j, datlen - j); 464 } 465 ARC4_UNLOCK_(); 466 } 467 #endif 468 469 #ifndef ARC4RANDOM_NORANDOM 470 ARC4RANDOM_EXPORT ARC4RANDOM_UINT32 471 arc4random(void) 472 { 473 ARC4RANDOM_UINT32 val; 474 ARC4_LOCK_(); 475 arc4_count -= 4; 476 arc4_stir_if_needed(); 477 val = arc4_getword(); 478 ARC4_UNLOCK_(); 479 return val; 480 } 481 #endif 482 483 ARC4RANDOM_EXPORT void 484 arc4random_buf(void *buf_, size_t n) 485 { 486 unsigned char *buf = buf_; 487 ARC4_LOCK_(); 488 arc4_stir_if_needed(); 489 while (n--) { 490 if (--arc4_count <= 0) 491 arc4_stir(); 492 buf[n] = arc4_getbyte(); 493 } 494 ARC4_UNLOCK_(); 495 } 496 497 #ifndef ARC4RANDOM_NOUNIFORM 498 /* 499 * Calculate a uniformly distributed random number less than upper_bound 500 * avoiding "modulo bias". 501 * 502 * Uniformity is achieved by generating new random numbers until the one 503 * returned is outside the range [0, 2**32 % upper_bound). This 504 * guarantees the selected random number will be inside 505 * [2**32 % upper_bound, 2**32) which maps back to [0, upper_bound) 506 * after reduction modulo upper_bound. 507 */ 508 ARC4RANDOM_EXPORT unsigned int 509 arc4random_uniform(unsigned int upper_bound) 510 { 511 ARC4RANDOM_UINT32 r, min; 512 513 if (upper_bound < 2) 514 return 0; 515 516 #if (UINT_MAX > 0xffffffffUL) 517 min = 0x100000000UL % upper_bound; 518 #else 519 /* Calculate (2**32 % upper_bound) avoiding 64-bit math */ 520 if (upper_bound > 0x80000000) 521 min = 1 + ~upper_bound; /* 2**32 - upper_bound */ 522 else { 523 /* (2**32 - (x * 2)) % x == 2**32 % x when x <= 2**31 */ 524 min = ((0xffffffff - (upper_bound * 2)) + 1) % upper_bound; 525 } 526 #endif 527 528 /* 529 * This could theoretically loop forever but each retry has 530 * p > 0.5 (worst case, usually far better) of selecting a 531 * number inside the range we need, so it should rarely need 532 * to re-roll. 533 */ 534 for (;;) { 535 r = arc4random(); 536 if (r >= min) 537 break; 538 } 539 540 return r % upper_bound; 541 } 542 #endif 543