1 /* 2 * PRNG: Pseudo Random Number Generator 3 * Based on NIST Recommended PRNG From ANSI X9.31 Appendix A.2.4 using 4 * AES 128 cipher 5 * 6 * (C) Neil Horman <nhorman@tuxdriver.com> 7 * 8 * This program is free software; you can redistribute it and/or modify it 9 * under the terms of the GNU General Public License as published by the 10 * Free Software Foundation; either version 2 of the License, or (at your 11 * any later version. 12 * 13 * 14 */ 15 16 #include <crypto/internal/rng.h> 17 #include <linux/err.h> 18 #include <linux/init.h> 19 #include <linux/module.h> 20 #include <linux/moduleparam.h> 21 #include <linux/string.h> 22 23 #include "internal.h" 24 25 #define DEFAULT_PRNG_KEY "0123456789abcdef" 26 #define DEFAULT_PRNG_KSZ 16 27 #define DEFAULT_BLK_SZ 16 28 #define DEFAULT_V_SEED "zaybxcwdveuftgsh" 29 30 /* 31 * Flags for the prng_context flags field 32 */ 33 34 #define PRNG_FIXED_SIZE 0x1 35 #define PRNG_NEED_RESET 0x2 36 37 /* 38 * Note: DT is our counter value 39 * I is our intermediate value 40 * V is our seed vector 41 * See http://csrc.nist.gov/groups/STM/cavp/documents/rng/931rngext.pdf 42 * for implementation details 43 */ 44 45 46 struct prng_context { 47 spinlock_t prng_lock; 48 unsigned char rand_data[DEFAULT_BLK_SZ]; 49 unsigned char last_rand_data[DEFAULT_BLK_SZ]; 50 unsigned char DT[DEFAULT_BLK_SZ]; 51 unsigned char I[DEFAULT_BLK_SZ]; 52 unsigned char V[DEFAULT_BLK_SZ]; 53 u32 rand_data_valid; 54 struct crypto_cipher *tfm; 55 u32 flags; 56 }; 57 58 static int dbg; 59 60 static void hexdump(char *note, unsigned char *buf, unsigned int len) 61 { 62 if (dbg) { 63 printk(KERN_CRIT "%s", note); 64 print_hex_dump(KERN_CONT, "", DUMP_PREFIX_OFFSET, 65 16, 1, 66 buf, len, false); 67 } 68 } 69 70 #define dbgprint(format, args...) do {\ 71 if (dbg)\ 72 printk(format, ##args);\ 73 } while (0) 74 75 static void xor_vectors(unsigned char *in1, unsigned char *in2, 76 unsigned char *out, unsigned int size) 77 { 78 int i; 79 80 for (i = 0; i < size; i++) 81 out[i] = in1[i] ^ in2[i]; 82 83 } 84 /* 85 * Returns DEFAULT_BLK_SZ bytes of random data per call 86 * returns 0 if generation succeeded, <0 if something went wrong 87 */ 88 static int _get_more_prng_bytes(struct prng_context *ctx, int cont_test) 89 { 90 int i; 91 unsigned char tmp[DEFAULT_BLK_SZ]; 92 unsigned char *output = NULL; 93 94 95 dbgprint(KERN_CRIT "Calling _get_more_prng_bytes for context %p\n", 96 ctx); 97 98 hexdump("Input DT: ", ctx->DT, DEFAULT_BLK_SZ); 99 hexdump("Input I: ", ctx->I, DEFAULT_BLK_SZ); 100 hexdump("Input V: ", ctx->V, DEFAULT_BLK_SZ); 101 102 /* 103 * This algorithm is a 3 stage state machine 104 */ 105 for (i = 0; i < 3; i++) { 106 107 switch (i) { 108 case 0: 109 /* 110 * Start by encrypting the counter value 111 * This gives us an intermediate value I 112 */ 113 memcpy(tmp, ctx->DT, DEFAULT_BLK_SZ); 114 output = ctx->I; 115 hexdump("tmp stage 0: ", tmp, DEFAULT_BLK_SZ); 116 break; 117 case 1: 118 119 /* 120 * Next xor I with our secret vector V 121 * encrypt that result to obtain our 122 * pseudo random data which we output 123 */ 124 xor_vectors(ctx->I, ctx->V, tmp, DEFAULT_BLK_SZ); 125 hexdump("tmp stage 1: ", tmp, DEFAULT_BLK_SZ); 126 output = ctx->rand_data; 127 break; 128 case 2: 129 /* 130 * First check that we didn't produce the same 131 * random data that we did last time around through this 132 */ 133 if (!memcmp(ctx->rand_data, ctx->last_rand_data, 134 DEFAULT_BLK_SZ)) { 135 if (cont_test) { 136 panic("cprng %p Failed repetition check!\n", 137 ctx); 138 } 139 140 printk(KERN_ERR 141 "ctx %p Failed repetition check!\n", 142 ctx); 143 144 ctx->flags |= PRNG_NEED_RESET; 145 return -EINVAL; 146 } 147 memcpy(ctx->last_rand_data, ctx->rand_data, 148 DEFAULT_BLK_SZ); 149 150 /* 151 * Lastly xor the random data with I 152 * and encrypt that to obtain a new secret vector V 153 */ 154 xor_vectors(ctx->rand_data, ctx->I, tmp, 155 DEFAULT_BLK_SZ); 156 output = ctx->V; 157 hexdump("tmp stage 2: ", tmp, DEFAULT_BLK_SZ); 158 break; 159 } 160 161 162 /* do the encryption */ 163 crypto_cipher_encrypt_one(ctx->tfm, output, tmp); 164 165 } 166 167 /* 168 * Now update our DT value 169 */ 170 for (i = DEFAULT_BLK_SZ - 1; i >= 0; i--) { 171 ctx->DT[i] += 1; 172 if (ctx->DT[i] != 0) 173 break; 174 } 175 176 dbgprint("Returning new block for context %p\n", ctx); 177 ctx->rand_data_valid = 0; 178 179 hexdump("Output DT: ", ctx->DT, DEFAULT_BLK_SZ); 180 hexdump("Output I: ", ctx->I, DEFAULT_BLK_SZ); 181 hexdump("Output V: ", ctx->V, DEFAULT_BLK_SZ); 182 hexdump("New Random Data: ", ctx->rand_data, DEFAULT_BLK_SZ); 183 184 return 0; 185 } 186 187 /* Our exported functions */ 188 static int get_prng_bytes(char *buf, size_t nbytes, struct prng_context *ctx, 189 int do_cont_test) 190 { 191 unsigned char *ptr = buf; 192 unsigned int byte_count = (unsigned int)nbytes; 193 int err; 194 195 196 spin_lock_bh(&ctx->prng_lock); 197 198 err = -EINVAL; 199 if (ctx->flags & PRNG_NEED_RESET) 200 goto done; 201 202 /* 203 * If the FIXED_SIZE flag is on, only return whole blocks of 204 * pseudo random data 205 */ 206 err = -EINVAL; 207 if (ctx->flags & PRNG_FIXED_SIZE) { 208 if (nbytes < DEFAULT_BLK_SZ) 209 goto done; 210 byte_count = DEFAULT_BLK_SZ; 211 } 212 213 err = byte_count; 214 215 dbgprint(KERN_CRIT "getting %d random bytes for context %p\n", 216 byte_count, ctx); 217 218 219 remainder: 220 if (ctx->rand_data_valid == DEFAULT_BLK_SZ) { 221 if (_get_more_prng_bytes(ctx, do_cont_test) < 0) { 222 memset(buf, 0, nbytes); 223 err = -EINVAL; 224 goto done; 225 } 226 } 227 228 /* 229 * Copy any data less than an entire block 230 */ 231 if (byte_count < DEFAULT_BLK_SZ) { 232 empty_rbuf: 233 while (ctx->rand_data_valid < DEFAULT_BLK_SZ) { 234 *ptr = ctx->rand_data[ctx->rand_data_valid]; 235 ptr++; 236 byte_count--; 237 ctx->rand_data_valid++; 238 if (byte_count == 0) 239 goto done; 240 } 241 } 242 243 /* 244 * Now copy whole blocks 245 */ 246 for (; byte_count >= DEFAULT_BLK_SZ; byte_count -= DEFAULT_BLK_SZ) { 247 if (ctx->rand_data_valid == DEFAULT_BLK_SZ) { 248 if (_get_more_prng_bytes(ctx, do_cont_test) < 0) { 249 memset(buf, 0, nbytes); 250 err = -EINVAL; 251 goto done; 252 } 253 } 254 if (ctx->rand_data_valid > 0) 255 goto empty_rbuf; 256 memcpy(ptr, ctx->rand_data, DEFAULT_BLK_SZ); 257 ctx->rand_data_valid += DEFAULT_BLK_SZ; 258 ptr += DEFAULT_BLK_SZ; 259 } 260 261 /* 262 * Now go back and get any remaining partial block 263 */ 264 if (byte_count) 265 goto remainder; 266 267 done: 268 spin_unlock_bh(&ctx->prng_lock); 269 dbgprint(KERN_CRIT "returning %d from get_prng_bytes in context %p\n", 270 err, ctx); 271 return err; 272 } 273 274 static void free_prng_context(struct prng_context *ctx) 275 { 276 crypto_free_cipher(ctx->tfm); 277 } 278 279 static int reset_prng_context(struct prng_context *ctx, 280 unsigned char *key, size_t klen, 281 unsigned char *V, unsigned char *DT) 282 { 283 int ret; 284 unsigned char *prng_key; 285 286 spin_lock_bh(&ctx->prng_lock); 287 ctx->flags |= PRNG_NEED_RESET; 288 289 prng_key = (key != NULL) ? key : (unsigned char *)DEFAULT_PRNG_KEY; 290 291 if (!key) 292 klen = DEFAULT_PRNG_KSZ; 293 294 if (V) 295 memcpy(ctx->V, V, DEFAULT_BLK_SZ); 296 else 297 memcpy(ctx->V, DEFAULT_V_SEED, DEFAULT_BLK_SZ); 298 299 if (DT) 300 memcpy(ctx->DT, DT, DEFAULT_BLK_SZ); 301 else 302 memset(ctx->DT, 0, DEFAULT_BLK_SZ); 303 304 memset(ctx->rand_data, 0, DEFAULT_BLK_SZ); 305 memset(ctx->last_rand_data, 0, DEFAULT_BLK_SZ); 306 307 ctx->rand_data_valid = DEFAULT_BLK_SZ; 308 309 ret = crypto_cipher_setkey(ctx->tfm, prng_key, klen); 310 if (ret) { 311 dbgprint(KERN_CRIT "PRNG: setkey() failed flags=%x\n", 312 crypto_cipher_get_flags(ctx->tfm)); 313 goto out; 314 } 315 316 ret = 0; 317 ctx->flags &= ~PRNG_NEED_RESET; 318 out: 319 spin_unlock_bh(&ctx->prng_lock); 320 return ret; 321 } 322 323 static int cprng_init(struct crypto_tfm *tfm) 324 { 325 struct prng_context *ctx = crypto_tfm_ctx(tfm); 326 327 spin_lock_init(&ctx->prng_lock); 328 ctx->tfm = crypto_alloc_cipher("aes", 0, 0); 329 if (IS_ERR(ctx->tfm)) { 330 dbgprint(KERN_CRIT "Failed to alloc tfm for context %p\n", 331 ctx); 332 return PTR_ERR(ctx->tfm); 333 } 334 335 if (reset_prng_context(ctx, NULL, DEFAULT_PRNG_KSZ, NULL, NULL) < 0) 336 return -EINVAL; 337 338 /* 339 * after allocation, we should always force the user to reset 340 * so they don't inadvertently use the insecure default values 341 * without specifying them intentially 342 */ 343 ctx->flags |= PRNG_NEED_RESET; 344 return 0; 345 } 346 347 static void cprng_exit(struct crypto_tfm *tfm) 348 { 349 free_prng_context(crypto_tfm_ctx(tfm)); 350 } 351 352 static int cprng_get_random(struct crypto_rng *tfm, u8 *rdata, 353 unsigned int dlen) 354 { 355 struct prng_context *prng = crypto_rng_ctx(tfm); 356 357 return get_prng_bytes(rdata, dlen, prng, 0); 358 } 359 360 /* 361 * This is the cprng_registered reset method the seed value is 362 * interpreted as the tuple { V KEY DT} 363 * V and KEY are required during reset, and DT is optional, detected 364 * as being present by testing the length of the seed 365 */ 366 static int cprng_reset(struct crypto_rng *tfm, u8 *seed, unsigned int slen) 367 { 368 struct prng_context *prng = crypto_rng_ctx(tfm); 369 u8 *key = seed + DEFAULT_BLK_SZ; 370 u8 *dt = NULL; 371 372 if (slen < DEFAULT_PRNG_KSZ + DEFAULT_BLK_SZ) 373 return -EINVAL; 374 375 if (slen >= (2 * DEFAULT_BLK_SZ + DEFAULT_PRNG_KSZ)) 376 dt = key + DEFAULT_PRNG_KSZ; 377 378 reset_prng_context(prng, key, DEFAULT_PRNG_KSZ, seed, dt); 379 380 if (prng->flags & PRNG_NEED_RESET) 381 return -EINVAL; 382 return 0; 383 } 384 385 #ifdef CONFIG_CRYPTO_FIPS 386 static int fips_cprng_get_random(struct crypto_rng *tfm, u8 *rdata, 387 unsigned int dlen) 388 { 389 struct prng_context *prng = crypto_rng_ctx(tfm); 390 391 return get_prng_bytes(rdata, dlen, prng, 1); 392 } 393 394 static int fips_cprng_reset(struct crypto_rng *tfm, u8 *seed, unsigned int slen) 395 { 396 u8 rdata[DEFAULT_BLK_SZ]; 397 u8 *key = seed + DEFAULT_BLK_SZ; 398 int rc; 399 400 struct prng_context *prng = crypto_rng_ctx(tfm); 401 402 if (slen < DEFAULT_PRNG_KSZ + DEFAULT_BLK_SZ) 403 return -EINVAL; 404 405 /* fips strictly requires seed != key */ 406 if (!memcmp(seed, key, DEFAULT_PRNG_KSZ)) 407 return -EINVAL; 408 409 rc = cprng_reset(tfm, seed, slen); 410 411 if (!rc) 412 goto out; 413 414 /* this primes our continuity test */ 415 rc = get_prng_bytes(rdata, DEFAULT_BLK_SZ, prng, 0); 416 prng->rand_data_valid = DEFAULT_BLK_SZ; 417 418 out: 419 return rc; 420 } 421 #endif 422 423 static struct crypto_alg rng_algs[] = { { 424 .cra_name = "stdrng", 425 .cra_driver_name = "ansi_cprng", 426 .cra_priority = 100, 427 .cra_flags = CRYPTO_ALG_TYPE_RNG, 428 .cra_ctxsize = sizeof(struct prng_context), 429 .cra_type = &crypto_rng_type, 430 .cra_module = THIS_MODULE, 431 .cra_init = cprng_init, 432 .cra_exit = cprng_exit, 433 .cra_u = { 434 .rng = { 435 .rng_make_random = cprng_get_random, 436 .rng_reset = cprng_reset, 437 .seedsize = DEFAULT_PRNG_KSZ + 2*DEFAULT_BLK_SZ, 438 } 439 } 440 #ifdef CONFIG_CRYPTO_FIPS 441 }, { 442 .cra_name = "fips(ansi_cprng)", 443 .cra_driver_name = "fips_ansi_cprng", 444 .cra_priority = 300, 445 .cra_flags = CRYPTO_ALG_TYPE_RNG, 446 .cra_ctxsize = sizeof(struct prng_context), 447 .cra_type = &crypto_rng_type, 448 .cra_module = THIS_MODULE, 449 .cra_init = cprng_init, 450 .cra_exit = cprng_exit, 451 .cra_u = { 452 .rng = { 453 .rng_make_random = fips_cprng_get_random, 454 .rng_reset = fips_cprng_reset, 455 .seedsize = DEFAULT_PRNG_KSZ + 2*DEFAULT_BLK_SZ, 456 } 457 } 458 #endif 459 } }; 460 461 /* Module initalization */ 462 static int __init prng_mod_init(void) 463 { 464 return crypto_register_algs(rng_algs, ARRAY_SIZE(rng_algs)); 465 } 466 467 static void __exit prng_mod_fini(void) 468 { 469 crypto_unregister_algs(rng_algs, ARRAY_SIZE(rng_algs)); 470 } 471 472 MODULE_LICENSE("GPL"); 473 MODULE_DESCRIPTION("Software Pseudo Random Number Generator"); 474 MODULE_AUTHOR("Neil Horman <nhorman@tuxdriver.com>"); 475 module_param(dbg, int, 0); 476 MODULE_PARM_DESC(dbg, "Boolean to enable debugging (0/1 == off/on)"); 477 module_init(prng_mod_init); 478 module_exit(prng_mod_fini); 479 MODULE_ALIAS("stdrng"); 480