1 /* 2 * Random number generator 3 * Copyright (c) 2010-2011, Jouni Malinen <j@w1.fi> 4 * 5 * This software may be distributed under the terms of the BSD license. 6 * See README for more details. 7 * 8 * This random number generator is used to provide additional entropy to the 9 * one provided by the operating system (os_get_random()) for session key 10 * generation. The os_get_random() output is expected to be secure and the 11 * implementation here is expected to provide only limited protection against 12 * cases where os_get_random() cannot provide strong randomness. This 13 * implementation shall not be assumed to be secure as the sole source of 14 * randomness. The random_get_bytes() function mixes in randomness from 15 * os_get_random() and as such, calls to os_get_random() can be replaced with 16 * calls to random_get_bytes() without reducing security. 17 * 18 * The design here follows partially the design used in the Linux 19 * drivers/char/random.c, but the implementation here is simpler and not as 20 * strong. This is a compromise to reduce duplicated CPU effort and to avoid 21 * extra code/memory size. As pointed out above, os_get_random() needs to be 22 * guaranteed to be secure for any of the security assumptions to hold. 23 */ 24 25 #include "utils/includes.h" 26 #ifdef __linux__ 27 #include <fcntl.h> 28 #ifdef CONFIG_GETRANDOM 29 #include <sys/random.h> 30 #endif /* CONFIG_GETRANDOM */ 31 #endif /* __linux__ */ 32 33 #include "utils/common.h" 34 #include "utils/eloop.h" 35 #include "crypto/crypto.h" 36 #include "sha1.h" 37 #include "random.h" 38 39 #define POOL_WORDS 32 40 #define POOL_WORDS_MASK (POOL_WORDS - 1) 41 #define POOL_TAP1 26 42 #define POOL_TAP2 20 43 #define POOL_TAP3 14 44 #define POOL_TAP4 7 45 #define POOL_TAP5 1 46 #define EXTRACT_LEN 16 47 #define MIN_READY_MARK 2 48 49 static u32 pool[POOL_WORDS]; 50 static unsigned int input_rotate = 0; 51 static unsigned int pool_pos = 0; 52 static u8 stub_key[20]; 53 #ifdef __linux__ 54 static size_t stub_key_avail = 0; 55 static int random_fd = -1; 56 #endif /* __linux__ */ 57 static unsigned int own_pool_ready = 0; 58 #define RANDOM_ENTROPY_SIZE 20 59 static char *random_entropy_file = NULL; 60 61 #define MIN_COLLECT_ENTROPY 1000 62 static unsigned int entropy = 0; 63 static unsigned int total_collected = 0; 64 65 66 static void random_write_entropy(void); 67 68 69 static u32 __ROL32(u32 x, u32 y) 70 { 71 if (y == 0) 72 return x; 73 74 return (x << (y & 31)) | (x >> (32 - (y & 31))); 75 } 76 77 78 static void random_mix_pool(const void *buf, size_t len) 79 { 80 static const u32 twist[8] = { 81 0x00000000, 0x3b6e20c8, 0x76dc4190, 0x4db26158, 82 0xedb88320, 0xd6d6a3e8, 0x9b64c2b0, 0xa00ae278 83 }; 84 const u8 *pos = buf; 85 u32 w; 86 87 wpa_hexdump_key(MSG_EXCESSIVE, "random_mix_pool", buf, len); 88 89 while (len--) { 90 w = __ROL32(*pos++, input_rotate & 31); 91 input_rotate += pool_pos ? 7 : 14; 92 pool_pos = (pool_pos - 1) & POOL_WORDS_MASK; 93 w ^= pool[pool_pos]; 94 w ^= pool[(pool_pos + POOL_TAP1) & POOL_WORDS_MASK]; 95 w ^= pool[(pool_pos + POOL_TAP2) & POOL_WORDS_MASK]; 96 w ^= pool[(pool_pos + POOL_TAP3) & POOL_WORDS_MASK]; 97 w ^= pool[(pool_pos + POOL_TAP4) & POOL_WORDS_MASK]; 98 w ^= pool[(pool_pos + POOL_TAP5) & POOL_WORDS_MASK]; 99 pool[pool_pos] = (w >> 3) ^ twist[w & 7]; 100 } 101 } 102 103 104 static void random_extract(u8 *out) 105 { 106 unsigned int i; 107 u8 hash[SHA1_MAC_LEN]; 108 u32 *hash_ptr; 109 u32 buf[POOL_WORDS / 2]; 110 111 /* First, add hash back to pool to make backtracking more difficult. */ 112 hmac_sha1(stub_key, sizeof(stub_key), (const u8 *) pool, 113 sizeof(pool), hash); 114 random_mix_pool(hash, sizeof(hash)); 115 /* Hash half the pool to extra data */ 116 for (i = 0; i < POOL_WORDS / 2; i++) 117 buf[i] = pool[(pool_pos - i) & POOL_WORDS_MASK]; 118 hmac_sha1(stub_key, sizeof(stub_key), (const u8 *) buf, 119 sizeof(buf), hash); 120 /* 121 * Fold the hash to further reduce any potential output pattern. 122 * Though, compromise this to reduce CPU use for the most common output 123 * length (32) and return 16 bytes from instead of only half. 124 */ 125 hash_ptr = (u32 *) hash; 126 hash_ptr[0] ^= hash_ptr[4]; 127 os_memcpy(out, hash, EXTRACT_LEN); 128 } 129 130 131 void random_add_randomness(const void *buf, size_t len) 132 { 133 struct os_time t; 134 static unsigned int count = 0; 135 136 count++; 137 if (entropy > MIN_COLLECT_ENTROPY && (count & 0x3ff) != 0) { 138 /* 139 * No need to add more entropy at this point, so save CPU and 140 * skip the update. 141 */ 142 return; 143 } 144 wpa_printf(MSG_EXCESSIVE, "Add randomness: count=%u entropy=%u", 145 count, entropy); 146 147 os_get_time(&t); 148 wpa_hexdump_key(MSG_EXCESSIVE, "random pool", 149 (const u8 *) pool, sizeof(pool)); 150 random_mix_pool(&t, sizeof(t)); 151 random_mix_pool(buf, len); 152 wpa_hexdump_key(MSG_EXCESSIVE, "random pool", 153 (const u8 *) pool, sizeof(pool)); 154 entropy++; 155 total_collected++; 156 } 157 158 159 int random_get_bytes(void *buf, size_t len) 160 { 161 int ret; 162 u8 *bytes = buf; 163 size_t left; 164 165 wpa_printf(MSG_MSGDUMP, "Get randomness: len=%u entropy=%u", 166 (unsigned int) len, entropy); 167 168 /* Start with assumed strong randomness from OS */ 169 ret = os_get_random(buf, len); 170 wpa_hexdump_key(MSG_EXCESSIVE, "random from os_get_random", 171 buf, len); 172 173 /* Mix in additional entropy extracted from the internal pool */ 174 left = len; 175 while (left) { 176 size_t siz, i; 177 u8 tmp[EXTRACT_LEN]; 178 random_extract(tmp); 179 wpa_hexdump_key(MSG_EXCESSIVE, "random from internal pool", 180 tmp, sizeof(tmp)); 181 siz = left > EXTRACT_LEN ? EXTRACT_LEN : left; 182 for (i = 0; i < siz; i++) 183 *bytes++ ^= tmp[i]; 184 left -= siz; 185 } 186 187 #ifdef CONFIG_FIPS 188 /* Mix in additional entropy from the crypto module */ 189 bytes = buf; 190 left = len; 191 while (left) { 192 size_t siz, i; 193 u8 tmp[EXTRACT_LEN]; 194 if (crypto_get_random(tmp, sizeof(tmp)) < 0) { 195 wpa_printf(MSG_ERROR, "random: No entropy available " 196 "for generating strong random bytes"); 197 return -1; 198 } 199 wpa_hexdump_key(MSG_EXCESSIVE, "random from crypto module", 200 tmp, sizeof(tmp)); 201 siz = left > EXTRACT_LEN ? EXTRACT_LEN : left; 202 for (i = 0; i < siz; i++) 203 *bytes++ ^= tmp[i]; 204 left -= siz; 205 } 206 #endif /* CONFIG_FIPS */ 207 208 wpa_hexdump_key(MSG_EXCESSIVE, "mixed random", buf, len); 209 210 if (entropy < len) 211 entropy = 0; 212 else 213 entropy -= len; 214 215 return ret; 216 } 217 218 219 int random_pool_ready(void) 220 { 221 #ifdef __linux__ 222 int fd; 223 ssize_t res; 224 225 /* 226 * Make sure that there is reasonable entropy available before allowing 227 * some key derivation operations to proceed. 228 */ 229 230 if (stub_key_avail == sizeof(stub_key)) 231 return 1; /* Already initialized - good to continue */ 232 233 /* 234 * Try to fetch some more data from the kernel high quality RNG. 235 * There may not be enough data available at this point, 236 * so use non-blocking read to avoid blocking the application 237 * completely. 238 */ 239 240 #ifdef CONFIG_GETRANDOM 241 res = getrandom(stub_key + stub_key_avail, 242 sizeof(stub_key) - stub_key_avail, GRND_NONBLOCK); 243 if (res < 0) { 244 if (errno == ENOSYS) { 245 wpa_printf(MSG_DEBUG, 246 "random: getrandom() not supported, falling back to /dev/random"); 247 } else { 248 wpa_printf(MSG_INFO, 249 "random: no data from getrandom(): %s", 250 strerror(errno)); 251 res = 0; 252 } 253 } 254 #else /* CONFIG_GETRANDOM */ 255 res = -1; 256 #endif /* CONFIG_GETRANDOM */ 257 if (res < 0) { 258 fd = open("/dev/random", O_RDONLY | O_NONBLOCK); 259 if (fd < 0) { 260 wpa_printf(MSG_ERROR, 261 "random: Cannot open /dev/random: %s", 262 strerror(errno)); 263 return -1; 264 } 265 266 res = read(fd, stub_key + stub_key_avail, 267 sizeof(stub_key) - stub_key_avail); 268 if (res < 0) { 269 wpa_printf(MSG_ERROR, 270 "random: Cannot read from /dev/random: %s", 271 strerror(errno)); 272 res = 0; 273 } 274 close(fd); 275 } 276 277 wpa_printf(MSG_DEBUG, "random: Got %u/%u random bytes", (unsigned) res, 278 (unsigned) (sizeof(stub_key) - stub_key_avail)); 279 stub_key_avail += res; 280 281 if (stub_key_avail == sizeof(stub_key)) { 282 if (own_pool_ready < MIN_READY_MARK) 283 own_pool_ready = MIN_READY_MARK; 284 random_write_entropy(); 285 return 1; 286 } 287 288 wpa_printf(MSG_INFO, "random: Only %u/%u bytes of strong " 289 "random data available", 290 (unsigned) stub_key_avail, (unsigned) sizeof(stub_key)); 291 292 if (own_pool_ready >= MIN_READY_MARK || 293 total_collected + 10 * own_pool_ready > MIN_COLLECT_ENTROPY) { 294 wpa_printf(MSG_INFO, "random: Allow operation to proceed " 295 "based on internal entropy"); 296 return 1; 297 } 298 299 wpa_printf(MSG_INFO, "random: Not enough entropy pool available for " 300 "secure operations"); 301 return 0; 302 #else /* __linux__ */ 303 /* TODO: could do similar checks on non-Linux platforms */ 304 return 1; 305 #endif /* __linux__ */ 306 } 307 308 309 void random_mark_pool_ready(void) 310 { 311 own_pool_ready++; 312 wpa_printf(MSG_DEBUG, "random: Mark internal entropy pool to be " 313 "ready (count=%u/%u)", own_pool_ready, MIN_READY_MARK); 314 random_write_entropy(); 315 } 316 317 318 #ifdef __linux__ 319 320 static void random_close_fd(void) 321 { 322 if (random_fd >= 0) { 323 eloop_unregister_read_sock(random_fd); 324 close(random_fd); 325 random_fd = -1; 326 } 327 } 328 329 330 static void random_read_fd(int sock, void *eloop_ctx, void *sock_ctx) 331 { 332 ssize_t res; 333 334 if (stub_key_avail == sizeof(stub_key)) { 335 random_close_fd(); 336 return; 337 } 338 339 res = read(sock, stub_key + stub_key_avail, 340 sizeof(stub_key) - stub_key_avail); 341 if (res < 0) { 342 wpa_printf(MSG_ERROR, "random: Cannot read from /dev/random: " 343 "%s", strerror(errno)); 344 return; 345 } 346 347 wpa_printf(MSG_DEBUG, "random: Got %u/%u bytes from /dev/random", 348 (unsigned) res, 349 (unsigned) (sizeof(stub_key) - stub_key_avail)); 350 stub_key_avail += res; 351 352 if (stub_key_avail == sizeof(stub_key)) { 353 random_close_fd(); 354 if (own_pool_ready < MIN_READY_MARK) 355 own_pool_ready = MIN_READY_MARK; 356 random_write_entropy(); 357 } 358 } 359 360 #endif /* __linux__ */ 361 362 363 static void random_read_entropy(void) 364 { 365 char *buf; 366 size_t len; 367 368 if (!random_entropy_file) 369 return; 370 371 buf = os_readfile(random_entropy_file, &len); 372 if (buf == NULL) 373 return; /* entropy file not yet available */ 374 375 if (len != 1 + RANDOM_ENTROPY_SIZE) { 376 wpa_printf(MSG_DEBUG, "random: Invalid entropy file %s", 377 random_entropy_file); 378 os_free(buf); 379 return; 380 } 381 382 own_pool_ready = (u8) buf[0]; 383 random_add_randomness(buf + 1, RANDOM_ENTROPY_SIZE); 384 os_free(buf); 385 wpa_printf(MSG_DEBUG, "random: Added entropy from %s " 386 "(own_pool_ready=%u)", 387 random_entropy_file, own_pool_ready); 388 } 389 390 391 static void random_write_entropy(void) 392 { 393 char buf[RANDOM_ENTROPY_SIZE]; 394 FILE *f; 395 u8 opr; 396 int fail = 0; 397 398 if (!random_entropy_file) 399 return; 400 401 if (random_get_bytes(buf, RANDOM_ENTROPY_SIZE) < 0) 402 return; 403 404 f = fopen(random_entropy_file, "wb"); 405 if (f == NULL) { 406 wpa_printf(MSG_ERROR, "random: Could not open entropy file %s " 407 "for writing", random_entropy_file); 408 return; 409 } 410 411 opr = own_pool_ready > 0xff ? 0xff : own_pool_ready; 412 if (fwrite(&opr, 1, 1, f) != 1 || 413 fwrite(buf, RANDOM_ENTROPY_SIZE, 1, f) != 1) 414 fail = 1; 415 fclose(f); 416 if (fail) { 417 wpa_printf(MSG_ERROR, "random: Could not write entropy data " 418 "to %s", random_entropy_file); 419 return; 420 } 421 422 wpa_printf(MSG_DEBUG, "random: Updated entropy file %s " 423 "(own_pool_ready=%u)", 424 random_entropy_file, own_pool_ready); 425 } 426 427 428 void random_init(const char *entropy_file) 429 { 430 os_free(random_entropy_file); 431 if (entropy_file) 432 random_entropy_file = os_strdup(entropy_file); 433 else 434 random_entropy_file = NULL; 435 random_read_entropy(); 436 437 #ifdef __linux__ 438 if (random_fd >= 0) 439 return; 440 441 #ifdef CONFIG_GETRANDOM 442 { 443 u8 stub; 444 445 if (getrandom(&stub, 0, GRND_NONBLOCK) == 0 || 446 errno != ENOSYS) { 447 wpa_printf(MSG_DEBUG, 448 "random: getrandom() support available"); 449 return; 450 } 451 } 452 #endif /* CONFIG_GETRANDOM */ 453 454 random_fd = open("/dev/random", O_RDONLY | O_NONBLOCK); 455 if (random_fd < 0) { 456 wpa_printf(MSG_ERROR, "random: Cannot open /dev/random: %s", 457 strerror(errno)); 458 return; 459 } 460 wpa_printf(MSG_DEBUG, "random: Trying to read entropy from " 461 "/dev/random"); 462 463 eloop_register_read_sock(random_fd, random_read_fd, NULL, NULL); 464 #endif /* __linux__ */ 465 466 random_write_entropy(); 467 } 468 469 470 void random_deinit(void) 471 { 472 #ifdef __linux__ 473 random_close_fd(); 474 #endif /* __linux__ */ 475 random_write_entropy(); 476 os_free(random_entropy_file); 477 random_entropy_file = NULL; 478 } 479