arc4random.c revision 1.29
1 /* $NetBSD: arc4random.c,v 1.29 2015/03/19 05:46:25 riastradh Exp $ */ 2 3 /*- 4 * Copyright (c) 2014 The NetBSD Foundation, Inc. 5 * All rights reserved. 6 * 7 * This code is derived from software contributed to The NetBSD Foundation 8 * by Taylor R. Campbell. 9 * 10 * Redistribution and use in source and binary forms, with or without 11 * modification, are permitted provided that the following conditions 12 * are met: 13 * 1. Redistributions of source code must retain the above copyright 14 * notice, this list of conditions and the following disclaimer. 15 * 2. Redistributions in binary form must reproduce the above copyright 16 * notice, this list of conditions and the following disclaimer in the 17 * documentation and/or other materials provided with the distribution. 18 * 19 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS 20 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED 21 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 22 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS 23 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 24 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 25 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 26 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 27 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 28 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 29 * POSSIBILITY OF SUCH DAMAGE. 30 */ 31 32 /* 33 * Legacy arc4random(3) API from OpenBSD reimplemented using the 34 * ChaCha20 PRF, with per-thread state. 35 * 36 * Security model: 37 * - An attacker who sees some outputs cannot predict past or future 38 * outputs. 39 * - An attacker who sees the PRNG state cannot predict past outputs. 40 * - An attacker who sees a child's PRNG state cannot predict past or 41 * future outputs in the parent, or in other children. 42 * 43 * The arc4random(3) API may abort the process if: 44 * 45 * (a) the crypto self-test fails, 46 * (b) pthread_atfork or thr_keycreate fail, or 47 * (c) sysctl(KERN_ARND) fails when reseeding the PRNG. 48 * 49 * The crypto self-test, pthread_atfork, and thr_keycreate occur only 50 * once, on the first use of any of the arc4random(3) API. KERN_ARND 51 * is unlikely to fail later unless the kernel is seriously broken. 52 */ 53 54 #include <sys/cdefs.h> 55 __RCSID("$NetBSD: arc4random.c,v 1.29 2015/03/19 05:46:25 riastradh Exp $"); 56 57 #include "namespace.h" 58 #include "reentrant.h" 59 60 #include <sys/bitops.h> 61 #include <sys/endian.h> 62 #include <sys/errno.h> 63 #include <sys/mman.h> 64 #include <sys/sysctl.h> 65 66 #include <assert.h> 67 #include <sha2.h> 68 #include <stdbool.h> 69 #include <stdint.h> 70 #include <stdlib.h> 71 #include <string.h> 72 #include <unistd.h> 73 74 #ifdef __weak_alias 75 __weak_alias(arc4random,_arc4random) 76 __weak_alias(arc4random_addrandom,_arc4random_addrandom) 77 __weak_alias(arc4random_buf,_arc4random_buf) 78 __weak_alias(arc4random_stir,_arc4random_stir) 79 __weak_alias(arc4random_uniform,_arc4random_uniform) 80 #endif 81 82 /* 83 * For standard ChaCha, use le32dec/le32enc. We don't need that for 84 * the purposes of a nondeterministic random number generator -- we 85 * don't need to be bit-for-bit compatible over any wire. 86 */ 87 88 static inline uint32_t 89 crypto_le32dec(const void *p) 90 { 91 uint32_t v; 92 93 (void)memcpy(&v, p, sizeof v); 94 95 return v; 96 } 97 98 static inline void 99 crypto_le32enc(void *p, uint32_t v) 100 { 101 102 (void)memcpy(p, &v, sizeof v); 103 } 104 105 /* ChaCha core */ 106 107 #define crypto_core_OUTPUTBYTES 64 108 #define crypto_core_INPUTBYTES 16 109 #define crypto_core_KEYBYTES 32 110 #define crypto_core_CONSTBYTES 16 111 112 #define crypto_core_ROUNDS 20 113 114 static uint32_t 115 rotate(uint32_t u, unsigned c) 116 { 117 118 return (u << c) | (u >> (32 - c)); 119 } 120 121 #define QUARTERROUND(a, b, c, d) do { \ 122 (a) += (b); (d) ^= (a); (d) = rotate((d), 16); \ 123 (c) += (d); (b) ^= (c); (b) = rotate((b), 12); \ 124 (a) += (b); (d) ^= (a); (d) = rotate((d), 8); \ 125 (c) += (d); (b) ^= (c); (b) = rotate((b), 7); \ 126 } while (/*CONSTCOND*/0) 127 128 const uint8_t crypto_core_constant32[16] = "expand 32-byte k"; 129 130 static void 131 crypto_core(uint8_t *out, const uint8_t *in, const uint8_t *k, 132 const uint8_t *c) 133 { 134 uint32_t x0,x1,x2,x3,x4,x5,x6,x7,x8,x9,x10,x11,x12,x13,x14,x15; 135 uint32_t j0,j1,j2,j3,j4,j5,j6,j7,j8,j9,j10,j11,j12,j13,j14,j15; 136 int i; 137 138 j0 = x0 = crypto_le32dec(c + 0); 139 j1 = x1 = crypto_le32dec(c + 4); 140 j2 = x2 = crypto_le32dec(c + 8); 141 j3 = x3 = crypto_le32dec(c + 12); 142 j4 = x4 = crypto_le32dec(k + 0); 143 j5 = x5 = crypto_le32dec(k + 4); 144 j6 = x6 = crypto_le32dec(k + 8); 145 j7 = x7 = crypto_le32dec(k + 12); 146 j8 = x8 = crypto_le32dec(k + 16); 147 j9 = x9 = crypto_le32dec(k + 20); 148 j10 = x10 = crypto_le32dec(k + 24); 149 j11 = x11 = crypto_le32dec(k + 28); 150 j12 = x12 = crypto_le32dec(in + 0); 151 j13 = x13 = crypto_le32dec(in + 4); 152 j14 = x14 = crypto_le32dec(in + 8); 153 j15 = x15 = crypto_le32dec(in + 12); 154 155 for (i = crypto_core_ROUNDS; i > 0; i -= 2) { 156 QUARTERROUND( x0, x4, x8,x12); 157 QUARTERROUND( x1, x5, x9,x13); 158 QUARTERROUND( x2, x6,x10,x14); 159 QUARTERROUND( x3, x7,x11,x15); 160 QUARTERROUND( x0, x5,x10,x15); 161 QUARTERROUND( x1, x6,x11,x12); 162 QUARTERROUND( x2, x7, x8,x13); 163 QUARTERROUND( x3, x4, x9,x14); 164 } 165 166 crypto_le32enc(out + 0, x0 + j0); 167 crypto_le32enc(out + 4, x1 + j1); 168 crypto_le32enc(out + 8, x2 + j2); 169 crypto_le32enc(out + 12, x3 + j3); 170 crypto_le32enc(out + 16, x4 + j4); 171 crypto_le32enc(out + 20, x5 + j5); 172 crypto_le32enc(out + 24, x6 + j6); 173 crypto_le32enc(out + 28, x7 + j7); 174 crypto_le32enc(out + 32, x8 + j8); 175 crypto_le32enc(out + 36, x9 + j9); 176 crypto_le32enc(out + 40, x10 + j10); 177 crypto_le32enc(out + 44, x11 + j11); 178 crypto_le32enc(out + 48, x12 + j12); 179 crypto_le32enc(out + 52, x13 + j13); 180 crypto_le32enc(out + 56, x14 + j14); 181 crypto_le32enc(out + 60, x15 + j15); 182 } 183 184 /* ChaCha self-test */ 185 186 #ifdef _DIAGNOSTIC 187 188 /* 189 * Test vector for ChaCha20 from 190 * <http://tools.ietf.org/html/draft-strombergson-chacha-test-vectors-00>, 191 * test vectors for ChaCha12 and ChaCha8 and for big-endian machines 192 * generated by the same crypto_core code with crypto_core_ROUNDS and 193 * crypto_le32enc/dec varied. 194 */ 195 196 static const uint8_t crypto_core_selftest_vector[64] = { 197 #if _BYTE_ORDER == _LITTLE_ENDIAN 198 # if crypto_core_ROUNDS == 8 199 0x3e,0x00,0xef,0x2f,0x89,0x5f,0x40,0xd6, 200 0x7f,0x5b,0xb8,0xe8,0x1f,0x09,0xa5,0xa1, 201 0x2c,0x84,0x0e,0xc3,0xce,0x9a,0x7f,0x3b, 202 0x18,0x1b,0xe1,0x88,0xef,0x71,0x1a,0x1e, 203 0x98,0x4c,0xe1,0x72,0xb9,0x21,0x6f,0x41, 204 0x9f,0x44,0x53,0x67,0x45,0x6d,0x56,0x19, 205 0x31,0x4a,0x42,0xa3,0xda,0x86,0xb0,0x01, 206 0x38,0x7b,0xfd,0xb8,0x0e,0x0c,0xfe,0x42, 207 # elif crypto_core_ROUNDS == 12 208 0x9b,0xf4,0x9a,0x6a,0x07,0x55,0xf9,0x53, 209 0x81,0x1f,0xce,0x12,0x5f,0x26,0x83,0xd5, 210 0x04,0x29,0xc3,0xbb,0x49,0xe0,0x74,0x14, 211 0x7e,0x00,0x89,0xa5,0x2e,0xae,0x15,0x5f, 212 0x05,0x64,0xf8,0x79,0xd2,0x7a,0xe3,0xc0, 213 0x2c,0xe8,0x28,0x34,0xac,0xfa,0x8c,0x79, 214 0x3a,0x62,0x9f,0x2c,0xa0,0xde,0x69,0x19, 215 0x61,0x0b,0xe8,0x2f,0x41,0x13,0x26,0xbe, 216 # elif crypto_core_ROUNDS == 20 217 0x76,0xb8,0xe0,0xad,0xa0,0xf1,0x3d,0x90, 218 0x40,0x5d,0x6a,0xe5,0x53,0x86,0xbd,0x28, 219 0xbd,0xd2,0x19,0xb8,0xa0,0x8d,0xed,0x1a, 220 0xa8,0x36,0xef,0xcc,0x8b,0x77,0x0d,0xc7, 221 0xda,0x41,0x59,0x7c,0x51,0x57,0x48,0x8d, 222 0x77,0x24,0xe0,0x3f,0xb8,0xd8,0x4a,0x37, 223 0x6a,0x43,0xb8,0xf4,0x15,0x18,0xa1,0x1c, 224 0xc3,0x87,0xb6,0x69,0xb2,0xee,0x65,0x86, 225 # else 226 # error crypto_core_ROUNDS must be 8, 12, or 20. 227 # endif 228 #elif _BYTE_ORDER == _BIG_ENDIAN 229 # if crypto_core_ROUNDS == 8 230 0x9a,0x13,0x07,0xe3,0x38,0x18,0x9e,0x99, 231 0x15,0x37,0x16,0x4d,0x04,0xe6,0x48,0x9a, 232 0x07,0xd6,0xe8,0x7a,0x02,0xf9,0xf5,0xc7, 233 0x3f,0xa9,0xc2,0x0a,0xe1,0xc6,0x62,0xea, 234 0x80,0xaf,0xb6,0x51,0xca,0x52,0x43,0x87, 235 0xe3,0xa6,0xa6,0x61,0x11,0xf5,0xe6,0xcf, 236 0x09,0x0f,0xdc,0x9d,0xc3,0xc3,0xbb,0x43, 237 0xd7,0xfa,0x70,0x42,0xbf,0xa5,0xee,0xa2, 238 # elif crypto_core_ROUNDS == 12 239 0xcf,0x6c,0x16,0x48,0xbf,0xf4,0xba,0x85, 240 0x32,0x69,0xd3,0x98,0xc8,0x7d,0xcd,0x3f, 241 0xdc,0x76,0x6b,0xa2,0x7b,0xcb,0x17,0x4d, 242 0x05,0xda,0xdd,0xd8,0x62,0x54,0xbf,0xe0, 243 0x65,0xed,0x0e,0xf4,0x01,0x7e,0x3c,0x05, 244 0x35,0xb2,0x7a,0x60,0xf3,0x8f,0x12,0x33, 245 0x24,0x60,0xcd,0x85,0xfe,0x4c,0xf3,0x39, 246 0xb1,0x0e,0x3e,0xe0,0xba,0xa6,0x2f,0xa9, 247 # elif crypto_core_ROUNDS == 20 248 0x83,0x8b,0xf8,0x75,0xf7,0xde,0x9d,0x8c, 249 0x33,0x14,0x72,0x28,0xd1,0xbe,0x88,0xe5, 250 0x94,0xb5,0xed,0xb8,0x56,0xb5,0x9e,0x0c, 251 0x64,0x6a,0xaf,0xd9,0xa7,0x49,0x10,0x59, 252 0xba,0x3a,0x82,0xf8,0x4a,0x70,0x9c,0x00, 253 0x82,0x2c,0xae,0xc6,0xd7,0x1c,0x2e,0xda, 254 0x2a,0xfb,0x61,0x70,0x2b,0xd1,0xbf,0x8b, 255 0x95,0xbc,0x23,0xb6,0x4b,0x60,0x02,0xec, 256 # else 257 # error crypto_core_ROUNDS must be 8, 12, or 20. 258 # endif 259 #else 260 # error Byte order must be little-endian or big-endian. 261 #endif 262 }; 263 264 static int 265 crypto_core_selftest(void) 266 { 267 const uint8_t nonce[crypto_core_INPUTBYTES] = {0}; 268 const uint8_t key[crypto_core_KEYBYTES] = {0}; 269 uint8_t block[64]; 270 unsigned i; 271 272 crypto_core(block, nonce, key, crypto_core_constant32); 273 for (i = 0; i < 64; i++) { 274 if (block[i] != crypto_core_selftest_vector[i]) 275 return EIO; 276 } 277 278 return 0; 279 } 280 281 #else /* !_DIAGNOSTIC */ 282 283 static int 284 crypto_core_selftest(void) 285 { 286 287 return 0; 288 } 289 290 #endif 291 292 /* PRNG */ 293 294 /* 295 * For a state s, rather than use ChaCha20 as a stream cipher to 296 * generate the concatenation ChaCha20_s(0) || ChaCha20_s(1) || ..., we 297 * split ChaCha20_s(0) into s' || x and yield x for the first request, 298 * split ChaCha20_s'(0) into s'' || y and yield y for the second 299 * request, &c. This provides backtracking resistance: an attacker who 300 * finds s'' can't recover s' or x. 301 */ 302 303 #define crypto_prng_SEEDBYTES crypto_core_KEYBYTES 304 #define crypto_prng_MAXOUTPUTBYTES \ 305 (crypto_core_OUTPUTBYTES - crypto_prng_SEEDBYTES) 306 307 struct crypto_prng { 308 uint8_t state[crypto_prng_SEEDBYTES]; 309 }; 310 311 static void 312 crypto_prng_seed(struct crypto_prng *prng, const void *seed) 313 { 314 315 (void)memcpy(prng->state, seed, crypto_prng_SEEDBYTES); 316 } 317 318 static void 319 crypto_prng_buf(struct crypto_prng *prng, void *buf, size_t n) 320 { 321 const uint8_t nonce[crypto_core_INPUTBYTES] = {0}; 322 uint8_t output[crypto_core_OUTPUTBYTES]; 323 324 _DIAGASSERT(n <= crypto_prng_MAXOUTPUTBYTES); 325 __CTASSERT(sizeof prng->state + crypto_prng_MAXOUTPUTBYTES 326 <= sizeof output); 327 328 crypto_core(output, nonce, prng->state, crypto_core_constant32); 329 (void)memcpy(prng->state, output, sizeof prng->state); 330 (void)memcpy(buf, output + sizeof prng->state, n); 331 (void)explicit_memset(output, 0, sizeof output); 332 } 333 334 /* One-time stream: expand short single-use secret into long secret */ 335 336 #define crypto_onetimestream_SEEDBYTES crypto_core_KEYBYTES 337 338 static void 339 crypto_onetimestream(const void *seed, void *buf, size_t n) 340 { 341 uint32_t nonce[crypto_core_INPUTBYTES / sizeof(uint32_t)] = {0}; 342 uint8_t block[crypto_core_OUTPUTBYTES]; 343 uint8_t *p8, *p32; 344 const uint8_t *nonce8 = (const uint8_t *)(void *)nonce; 345 size_t ni, nb, nf; 346 347 /* 348 * Guarantee we can generate up to n bytes. We have 349 * 2^(8*INPUTBYTES) possible inputs yielding output of 350 * OUTPUTBYTES*2^(8*INPUTBYTES) bytes. It suffices to require 351 * that sizeof n > (1/CHAR_BIT) log_2 n be less than 352 * (1/CHAR_BIT) log_2 of the total output stream length. We 353 * have 354 * 355 * log_2 (o 2^(8 i)) = log_2 o + log_2 2^(8 i) 356 * = log_2 o + 8 i. 357 */ 358 __CTASSERT(CHAR_BIT * sizeof n <= 359 (/*LINTED*/ilog2(crypto_core_OUTPUTBYTES) + 8 * crypto_core_INPUTBYTES)); 360 361 p8 = buf; 362 p32 = (uint8_t *)roundup2((uintptr_t)p8, 4); 363 ni = p32 - p8; 364 if (n < ni) 365 ni = n; 366 nb = (n - ni) / sizeof block; 367 nf = (n - ni) % sizeof block; 368 369 _DIAGASSERT(((uintptr_t)p32 & 3) == 0); 370 _DIAGASSERT(ni <= n); 371 _DIAGASSERT(nb <= (n / sizeof block)); 372 _DIAGASSERT(nf <= n); 373 _DIAGASSERT(n == (ni + (nb * sizeof block) + nf)); 374 _DIAGASSERT(ni < 4); 375 _DIAGASSERT(nf < sizeof block); 376 377 if (ni) { 378 crypto_core(block, nonce8, seed, crypto_core_constant32); 379 nonce[0]++; 380 (void)memcpy(p8, block, ni); 381 } 382 while (nb--) { 383 crypto_core(p32, nonce8, seed, crypto_core_constant32); 384 if (++nonce[0] == 0) 385 nonce[1]++; 386 p32 += crypto_core_OUTPUTBYTES; 387 } 388 if (nf) { 389 crypto_core(block, nonce8, seed, crypto_core_constant32); 390 if (++nonce[0] == 0) 391 nonce[1]++; 392 (void)memcpy(p32, block, nf); 393 } 394 395 if (ni | nf) 396 (void)explicit_memset(block, 0, sizeof block); 397 } 398 399 /* arc4random state: per-thread, per-process (zeroed in child on fork) */ 400 401 struct arc4random_prng { 402 struct crypto_prng arc4_prng; 403 bool arc4_seeded; 404 }; 405 406 static void 407 arc4random_prng_addrandom(struct arc4random_prng *prng, const void *data, 408 size_t datalen) 409 { 410 const int mib[] = { CTL_KERN, KERN_ARND }; 411 SHA256_CTX ctx; 412 uint8_t buf[crypto_prng_SEEDBYTES]; 413 size_t buflen = sizeof buf; 414 415 __CTASSERT(sizeof buf == SHA256_DIGEST_LENGTH); 416 417 SHA256_Init(&ctx); 418 419 crypto_prng_buf(&prng->arc4_prng, buf, sizeof buf); 420 SHA256_Update(&ctx, buf, sizeof buf); 421 422 if (sysctl(mib, (u_int)__arraycount(mib), buf, &buflen, NULL, 0) == -1) 423 abort(); 424 if (buflen != sizeof buf) 425 abort(); 426 SHA256_Update(&ctx, buf, sizeof buf); 427 428 if (data != NULL) 429 SHA256_Update(&ctx, data, datalen); 430 431 SHA256_Final(buf, &ctx); 432 (void)explicit_memset(&ctx, 0, sizeof ctx); 433 434 /* reseed(SHA256(prng() || sysctl(KERN_ARND) || data)) */ 435 crypto_prng_seed(&prng->arc4_prng, buf); 436 (void)explicit_memset(buf, 0, sizeof buf); 437 prng->arc4_seeded = true; 438 } 439 440 #ifdef _REENTRANT 441 static struct arc4random_prng * 442 arc4random_prng_create(void) 443 { 444 struct arc4random_prng *prng; 445 const size_t size = roundup(sizeof(*prng), sysconf(_SC_PAGESIZE)); 446 447 prng = mmap(NULL, size, PROT_READ|PROT_WRITE, MAP_ANON, -1, 0); 448 if (prng == MAP_FAILED) 449 goto fail0; 450 if (minherit(prng, size, MAP_INHERIT_ZERO) == -1) 451 goto fail1; 452 453 return prng; 454 455 fail1: (void)munmap(prng, size); 456 fail0: return NULL; 457 } 458 #endif 459 460 #ifdef _REENTRANT 461 static void 462 arc4random_prng_destroy(struct arc4random_prng *prng) 463 { 464 const size_t size = roundup(sizeof(*prng), sysconf(_SC_PAGESIZE)); 465 466 (void)explicit_memset(prng, 0, sizeof(*prng)); 467 (void)munmap(prng, size); 468 } 469 #endif 470 471 /* Library state */ 472 473 static struct arc4random_global { 474 #ifdef _REENTRANT 475 mutex_t lock; 476 thread_key_t thread_key; 477 #endif 478 struct arc4random_prng prng; 479 bool initialized; 480 } arc4random_global = { 481 #ifdef _REENTRANT 482 .lock = MUTEX_INITIALIZER, 483 #endif 484 .initialized = false, 485 }; 486 487 static void 488 arc4random_atfork_prepare(void) 489 { 490 491 mutex_lock(&arc4random_global.lock); 492 (void)explicit_memset(&arc4random_global.prng, 0, 493 sizeof arc4random_global.prng); 494 } 495 496 static void 497 arc4random_atfork_parent(void) 498 { 499 500 mutex_unlock(&arc4random_global.lock); 501 } 502 503 static void 504 arc4random_atfork_child(void) 505 { 506 507 mutex_unlock(&arc4random_global.lock); 508 } 509 510 #ifdef _REENTRANT 511 static void 512 arc4random_tsd_destructor(void *p) 513 { 514 struct arc4random_prng *const prng = p; 515 516 arc4random_prng_destroy(prng); 517 } 518 #endif 519 520 static void 521 arc4random_initialize(void) 522 { 523 524 mutex_lock(&arc4random_global.lock); 525 if (!arc4random_global.initialized) { 526 if (crypto_core_selftest() != 0) 527 abort(); 528 if (pthread_atfork(&arc4random_atfork_prepare, 529 &arc4random_atfork_parent, &arc4random_atfork_child) 530 != 0) 531 abort(); 532 #ifdef _REENTRANT 533 if (thr_keycreate(&arc4random_global.thread_key, 534 &arc4random_tsd_destructor) != 0) 535 abort(); 536 #endif 537 arc4random_global.initialized = true; 538 } 539 mutex_unlock(&arc4random_global.lock); 540 } 541 542 static struct arc4random_prng * 543 arc4random_prng_get(void) 544 { 545 struct arc4random_prng *prng = NULL; 546 547 /* Make sure the library is initialized. */ 548 if (__predict_false(!arc4random_global.initialized)) 549 arc4random_initialize(); 550 551 #ifdef _REENTRANT 552 /* Get or create the per-thread PRNG state. */ 553 prng = thr_getspecific(arc4random_global.thread_key); 554 if (__predict_false(prng == NULL)) { 555 prng = arc4random_prng_create(); 556 thr_setspecific(arc4random_global.thread_key, prng); 557 } 558 #endif 559 560 /* If we can't create it, fall back to the global PRNG. */ 561 if (__predict_false(prng == NULL)) { 562 mutex_lock(&arc4random_global.lock); 563 prng = &arc4random_global.prng; 564 } 565 566 /* Guarantee the PRNG is seeded. */ 567 if (__predict_false(!prng->arc4_seeded)) 568 arc4random_prng_addrandom(prng, NULL, 0); 569 570 return prng; 571 } 572 573 static void 574 arc4random_prng_put(struct arc4random_prng *prng) 575 { 576 577 /* If we had fallen back to the global PRNG, unlock it. */ 578 if (__predict_false(prng == &arc4random_global.prng)) 579 mutex_unlock(&arc4random_global.lock); 580 } 581 582 /* Public API */ 583 584 uint32_t 585 arc4random(void) 586 { 587 struct arc4random_prng *prng; 588 uint32_t v; 589 590 prng = arc4random_prng_get(); 591 crypto_prng_buf(&prng->arc4_prng, &v, sizeof v); 592 arc4random_prng_put(prng); 593 594 return v; 595 } 596 597 void 598 arc4random_buf(void *buf, size_t len) 599 { 600 struct arc4random_prng *prng; 601 602 if (len <= crypto_prng_MAXOUTPUTBYTES) { 603 prng = arc4random_prng_get(); 604 crypto_prng_buf(&prng->arc4_prng, buf, len); 605 arc4random_prng_put(prng); 606 } else { 607 uint8_t seed[crypto_onetimestream_SEEDBYTES]; 608 609 prng = arc4random_prng_get(); 610 crypto_prng_buf(&prng->arc4_prng, seed, sizeof seed); 611 arc4random_prng_put(prng); 612 613 crypto_onetimestream(seed, buf, len); 614 (void)explicit_memset(seed, 0, sizeof seed); 615 } 616 } 617 618 uint32_t 619 arc4random_uniform(uint32_t bound) 620 { 621 struct arc4random_prng *prng; 622 uint32_t minimum, r; 623 624 /* 625 * We want a uniform random choice in [0, n), and arc4random() 626 * makes a uniform random choice in [0, 2^32). If we reduce 627 * that modulo n, values in [0, 2^32 mod n) will be represented 628 * slightly more than values in [2^32 mod n, n). Instead we 629 * choose only from [2^32 mod n, 2^32) by rejecting samples in 630 * [0, 2^32 mod n), to avoid counting the extra representative 631 * of [0, 2^32 mod n). To compute 2^32 mod n, note that 632 * 633 * 2^32 mod n = 2^32 mod n - 0 634 * = 2^32 mod n - n mod n 635 * = (2^32 - n) mod n, 636 * 637 * the last of which is what we compute in 32-bit arithmetic. 638 */ 639 minimum = (-bound % bound); 640 641 prng = arc4random_prng_get(); 642 do crypto_prng_buf(&prng->arc4_prng, &r, sizeof r); 643 while (__predict_false(r < minimum)); 644 arc4random_prng_put(prng); 645 646 return (r % bound); 647 } 648 649 void 650 arc4random_stir(void) 651 { 652 struct arc4random_prng *prng; 653 654 prng = arc4random_prng_get(); 655 arc4random_prng_addrandom(prng, NULL, 0); 656 arc4random_prng_put(prng); 657 } 658 659 /* 660 * Silly signature here is for hysterical raisins. Should instead be 661 * const void *data and size_t datalen. 662 */ 663 void 664 arc4random_addrandom(u_char *data, int datalen) 665 { 666 struct arc4random_prng *prng; 667 668 _DIAGASSERT(0 <= datalen); 669 670 prng = arc4random_prng_get(); 671 arc4random_prng_addrandom(prng, data, datalen); 672 arc4random_prng_put(prng); 673 } 674 675 #ifdef _ARC4RANDOM_TEST 676 677 #include <sys/wait.h> 678 679 #include <err.h> 680 #include <stdio.h> 681 682 int 683 main(int argc __unused, char **argv __unused) 684 { 685 unsigned char gubbish[] = "random gubbish"; 686 const uint8_t zero64[64] = {0}; 687 uint8_t buf[2048]; 688 unsigned i, a, n; 689 690 /* Test arc4random: should not be deterministic. */ 691 if (printf("arc4random: %08"PRIx32"\n", arc4random()) < 0) 692 err(1, "printf"); 693 694 /* Test stirring: should definitely not be deterministic. */ 695 arc4random_stir(); 696 697 /* Test small buffer. */ 698 arc4random_buf(buf, 8); 699 if (printf("arc4randombuf small:") < 0) 700 err(1, "printf"); 701 for (i = 0; i < 8; i++) 702 if (printf(" %02x", buf[i]) < 0) 703 err(1, "printf"); 704 if (printf("\n") < 0) 705 err(1, "printf"); 706 707 /* Test addrandom: should not make the rest deterministic. */ 708 arc4random_addrandom(gubbish, sizeof gubbish); 709 710 /* Test large buffer. */ 711 arc4random_buf(buf, sizeof buf); 712 if (printf("arc4randombuf_large:") < 0) 713 err(1, "printf"); 714 for (i = 0; i < sizeof buf; i++) 715 if (printf(" %02x", buf[i]) < 0) 716 err(1, "printf"); 717 if (printf("\n") < 0) 718 err(1, "printf"); 719 720 /* Test misaligned small and large. */ 721 for (a = 0; a < 64; a++) { 722 for (n = a; n < sizeof buf; n++) { 723 (void)memset(buf, 0, sizeof buf); 724 arc4random_buf(buf, n - a); 725 if (memcmp(buf + n - a, zero64, a) != 0) 726 errx(1, "arc4random buffer overflow 0"); 727 728 (void)memset(buf, 0, sizeof buf); 729 arc4random_buf(buf + a, n - a); 730 if (memcmp(buf, zero64, a) != 0) 731 errx(1, "arc4random buffer overflow 1"); 732 733 if ((2*a) <= n) { 734 (void)memset(buf, 0, sizeof buf); 735 arc4random_buf(buf + a, n - a - a); 736 if (memcmp(buf + n - a, zero64, a) != 0) 737 errx(1, 738 "arc4random buffer overflow 2"); 739 } 740 } 741 } 742 743 /* Test fork-safety. */ 744 { 745 pid_t pid, rpid; 746 int status; 747 748 pid = fork(); 749 switch (pid) { 750 case -1: 751 err(1, "fork"); 752 case 0: 753 _exit(arc4random_prng_get()->arc4_seeded); 754 default: 755 rpid = waitpid(pid, &status, 0); 756 if (rpid == -1) 757 err(1, "waitpid"); 758 if (rpid != pid) 759 errx(1, "waitpid returned wrong pid" 760 ": %"PRIdMAX" != %"PRIdMAX, 761 (intmax_t)rpid, 762 (intmax_t)pid); 763 if (WIFEXITED(status)) { 764 if (WEXITSTATUS(status) != 0) 765 errx(1, "child exited with %d", 766 WEXITSTATUS(status)); 767 } else if (WIFSIGNALED(status)) { 768 errx(1, "child terminated on signal %d", 769 WTERMSIG(status)); 770 } else { 771 errx(1, "child died mysteriously: %d", status); 772 } 773 } 774 } 775 776 /* XXX Test multithreaded fork safety...? */ 777 778 return 0; 779 } 780 #endif 781
Indexes created Mon Sep 29 21:09:56 GMT 2025