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 succeded, <0 if something went wrong 87 */ 88 static int _get_more_prng_bytes(struct prng_context *ctx) 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 (fips_enabled) { 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 { 190 unsigned char *ptr = buf; 191 unsigned int byte_count = (unsigned int)nbytes; 192 int err; 193 194 195 if (nbytes < 0) 196 return -EINVAL; 197 198 spin_lock_bh(&ctx->prng_lock); 199 200 err = -EINVAL; 201 if (ctx->flags & PRNG_NEED_RESET) 202 goto done; 203 204 /* 205 * If the FIXED_SIZE flag is on, only return whole blocks of 206 * pseudo random data 207 */ 208 err = -EINVAL; 209 if (ctx->flags & PRNG_FIXED_SIZE) { 210 if (nbytes < DEFAULT_BLK_SZ) 211 goto done; 212 byte_count = DEFAULT_BLK_SZ; 213 } 214 215 err = byte_count; 216 217 dbgprint(KERN_CRIT "getting %d random bytes for context %p\n", 218 byte_count, ctx); 219 220 221 remainder: 222 if (ctx->rand_data_valid == DEFAULT_BLK_SZ) { 223 if (_get_more_prng_bytes(ctx) < 0) { 224 memset(buf, 0, nbytes); 225 err = -EINVAL; 226 goto done; 227 } 228 } 229 230 /* 231 * Copy any data less than an entire block 232 */ 233 if (byte_count < DEFAULT_BLK_SZ) { 234 empty_rbuf: 235 for (; ctx->rand_data_valid < DEFAULT_BLK_SZ; 236 ctx->rand_data_valid++) { 237 *ptr = ctx->rand_data[ctx->rand_data_valid]; 238 ptr++; 239 byte_count--; 240 if (byte_count == 0) 241 goto done; 242 } 243 } 244 245 /* 246 * Now copy whole blocks 247 */ 248 for (; byte_count >= DEFAULT_BLK_SZ; byte_count -= DEFAULT_BLK_SZ) { 249 if (ctx->rand_data_valid == DEFAULT_BLK_SZ) { 250 if (_get_more_prng_bytes(ctx) < 0) { 251 memset(buf, 0, nbytes); 252 err = -EINVAL; 253 goto done; 254 } 255 } 256 if (ctx->rand_data_valid > 0) 257 goto empty_rbuf; 258 memcpy(ptr, ctx->rand_data, DEFAULT_BLK_SZ); 259 ctx->rand_data_valid += DEFAULT_BLK_SZ; 260 ptr += DEFAULT_BLK_SZ; 261 } 262 263 /* 264 * Now go back and get any remaining partial block 265 */ 266 if (byte_count) 267 goto remainder; 268 269 done: 270 spin_unlock_bh(&ctx->prng_lock); 271 dbgprint(KERN_CRIT "returning %d from get_prng_bytes in context %p\n", 272 err, ctx); 273 return err; 274 } 275 276 static void free_prng_context(struct prng_context *ctx) 277 { 278 crypto_free_cipher(ctx->tfm); 279 } 280 281 static int reset_prng_context(struct prng_context *ctx, 282 unsigned char *key, size_t klen, 283 unsigned char *V, unsigned char *DT) 284 { 285 int ret; 286 unsigned char *prng_key; 287 288 spin_lock_bh(&ctx->prng_lock); 289 ctx->flags |= PRNG_NEED_RESET; 290 291 prng_key = (key != NULL) ? key : (unsigned char *)DEFAULT_PRNG_KEY; 292 293 if (!key) 294 klen = DEFAULT_PRNG_KSZ; 295 296 if (V) 297 memcpy(ctx->V, V, DEFAULT_BLK_SZ); 298 else 299 memcpy(ctx->V, DEFAULT_V_SEED, DEFAULT_BLK_SZ); 300 301 if (DT) 302 memcpy(ctx->DT, DT, DEFAULT_BLK_SZ); 303 else 304 memset(ctx->DT, 0, DEFAULT_BLK_SZ); 305 306 memset(ctx->rand_data, 0, DEFAULT_BLK_SZ); 307 memset(ctx->last_rand_data, 0, DEFAULT_BLK_SZ); 308 309 ctx->rand_data_valid = DEFAULT_BLK_SZ; 310 311 ret = crypto_cipher_setkey(ctx->tfm, prng_key, klen); 312 if (ret) { 313 dbgprint(KERN_CRIT "PRNG: setkey() failed flags=%x\n", 314 crypto_cipher_get_flags(ctx->tfm)); 315 goto out; 316 } 317 318 ret = 0; 319 ctx->flags &= ~PRNG_NEED_RESET; 320 out: 321 spin_unlock_bh(&ctx->prng_lock); 322 return ret; 323 } 324 325 static int cprng_init(struct crypto_tfm *tfm) 326 { 327 struct prng_context *ctx = crypto_tfm_ctx(tfm); 328 329 spin_lock_init(&ctx->prng_lock); 330 ctx->tfm = crypto_alloc_cipher("aes", 0, 0); 331 if (IS_ERR(ctx->tfm)) { 332 dbgprint(KERN_CRIT "Failed to alloc tfm for context %p\n", 333 ctx); 334 return PTR_ERR(ctx->tfm); 335 } 336 337 if (reset_prng_context(ctx, NULL, DEFAULT_PRNG_KSZ, NULL, NULL) < 0) 338 return -EINVAL; 339 340 /* 341 * after allocation, we should always force the user to reset 342 * so they don't inadvertently use the insecure default values 343 * without specifying them intentially 344 */ 345 ctx->flags |= PRNG_NEED_RESET; 346 return 0; 347 } 348 349 static void cprng_exit(struct crypto_tfm *tfm) 350 { 351 free_prng_context(crypto_tfm_ctx(tfm)); 352 } 353 354 static int cprng_get_random(struct crypto_rng *tfm, u8 *rdata, 355 unsigned int dlen) 356 { 357 struct prng_context *prng = crypto_rng_ctx(tfm); 358 359 return get_prng_bytes(rdata, dlen, prng); 360 } 361 362 /* 363 * This is the cprng_registered reset method the seed value is 364 * interpreted as the tuple { V KEY DT} 365 * V and KEY are required during reset, and DT is optional, detected 366 * as being present by testing the length of the seed 367 */ 368 static int cprng_reset(struct crypto_rng *tfm, u8 *seed, unsigned int slen) 369 { 370 struct prng_context *prng = crypto_rng_ctx(tfm); 371 u8 *key = seed + DEFAULT_BLK_SZ; 372 u8 *dt = NULL; 373 374 if (slen < DEFAULT_PRNG_KSZ + DEFAULT_BLK_SZ) 375 return -EINVAL; 376 377 if (slen >= (2 * DEFAULT_BLK_SZ + DEFAULT_PRNG_KSZ)) 378 dt = key + DEFAULT_PRNG_KSZ; 379 380 reset_prng_context(prng, key, DEFAULT_PRNG_KSZ, seed, dt); 381 382 if (prng->flags & PRNG_NEED_RESET) 383 return -EINVAL; 384 return 0; 385 } 386 387 static struct crypto_alg rng_alg = { 388 .cra_name = "stdrng", 389 .cra_driver_name = "ansi_cprng", 390 .cra_priority = 100, 391 .cra_flags = CRYPTO_ALG_TYPE_RNG, 392 .cra_ctxsize = sizeof(struct prng_context), 393 .cra_type = &crypto_rng_type, 394 .cra_module = THIS_MODULE, 395 .cra_list = LIST_HEAD_INIT(rng_alg.cra_list), 396 .cra_init = cprng_init, 397 .cra_exit = cprng_exit, 398 .cra_u = { 399 .rng = { 400 .rng_make_random = cprng_get_random, 401 .rng_reset = cprng_reset, 402 .seedsize = DEFAULT_PRNG_KSZ + 2*DEFAULT_BLK_SZ, 403 } 404 } 405 }; 406 407 408 /* Module initalization */ 409 static int __init prng_mod_init(void) 410 { 411 if (fips_enabled) 412 rng_alg.cra_priority += 200; 413 414 return crypto_register_alg(&rng_alg); 415 } 416 417 static void __exit prng_mod_fini(void) 418 { 419 crypto_unregister_alg(&rng_alg); 420 return; 421 } 422 423 MODULE_LICENSE("GPL"); 424 MODULE_DESCRIPTION("Software Pseudo Random Number Generator"); 425 MODULE_AUTHOR("Neil Horman <nhorman@tuxdriver.com>"); 426 module_param(dbg, int, 0); 427 MODULE_PARM_DESC(dbg, "Boolean to enable debugging (0/1 == off/on)"); 428 module_init(prng_mod_init); 429 module_exit(prng_mod_fini); 430 MODULE_ALIAS("stdrng"); 431