crypto/ansi_cprng.c

   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 #define DEFAULT_PRNG_KEY "0123456789abcdef"
  24 #define DEFAULT_PRNG_KSZ 16
  25 #define DEFAULT_BLK_SZ 16
  26 #define DEFAULT_V_SEED "zaybxcwdveuftgsh"
  27
  28 /*
  29  * Flags for the prng_context flags field
  30  */
  31
  32 #define PRNG_FIXED_SIZE 0x1
  33 #define PRNG_NEED_RESET 0x2
  34
  35 /*
  36  * Note: DT is our counter value
  37  *       I is our intermediate value
  38  *       V is our seed vector
  39  * See http://csrc.nist.gov/groups/STM/cavp/documents/rng/931rngext.pdf
  40  * for implementation details
  41  */
  42
  43
  44 struct prng_context {
  45         spinlock_t prng_lock;
  46         unsigned char rand_data[DEFAULT_BLK_SZ];
  47         unsigned char last_rand_data[DEFAULT_BLK_SZ];
  48         unsigned char DT[DEFAULT_BLK_SZ];
  49         unsigned char I[DEFAULT_BLK_SZ];
  50         unsigned char V[DEFAULT_BLK_SZ];
  51         u32 rand_data_valid;
  52         struct crypto_cipher *tfm;
  53         u32 flags;
  54 };
  55
  56 static int dbg;
  57
  58 static void hexdump(char *note, unsigned char *buf, unsigned int len)
  59 {
  60         if (dbg) {
  61                 printk(KERN_CRIT "%s", note);
  62                 print_hex_dump(KERN_CONT, "", DUMP_PREFIX_OFFSET,
  63                                 16, 1,
  64                                 buf, len, false);
  65         }
  66 }
  67
  68 #define dbgprint(format, args...) do {\
  69 if (dbg)\
  70         printk(format, ##args);\
  71 } while (0)
  72
  73 static void xor_vectors(unsigned char *in1, unsigned char *in2,
  74                         unsigned char *out, unsigned int size)
  75 {
  76         int i;
  77
  78         for (i = 0; i < size; i++)
  79                 out[i] = in1[i] ^ in2[i];
  80
  81 }
  82 /*
  83  * Returns DEFAULT_BLK_SZ bytes of random data per call
  84  * returns 0 if generation succeeded, <0 if something went wrong
  85  */
  86 static int _get_more_prng_bytes(struct prng_context *ctx, int cont_test)
  87 {
  88         int i;
  89         unsigned char tmp[DEFAULT_BLK_SZ];
  90         unsigned char *output = NULL;
  91
  92
  93         dbgprint(KERN_CRIT "Calling _get_more_prng_bytes for context %p\n",
  94                 ctx);
  95
  96         hexdump("Input DT: ", ctx->DT, DEFAULT_BLK_SZ);
  97         hexdump("Input I: ", ctx->I, DEFAULT_BLK_SZ);
  98         hexdump("Input V: ", ctx->V, DEFAULT_BLK_SZ);
  99
 100         /*
 101          * This algorithm is a 3 stage state machine
 102          */
 103         for (i = 0; i < 3; i++) {
 104
 105                 switch (i) {
 106                 case 0:
 107                         /*
 108                          * Start by encrypting the counter value
 109                          * This gives us an intermediate value I
 110                          */
 111                         memcpy(tmp, ctx->DT, DEFAULT_BLK_SZ);
 112                         output = ctx->I;
 113                         hexdump("tmp stage 0: ", tmp, DEFAULT_BLK_SZ);
 114                         break;
 115                 case 1:
 116
 117                         /*
 118                          * Next xor I with our secret vector V
 119                          * encrypt that result to obtain our
 120                          * pseudo random data which we output
 121                          */
 122                         xor_vectors(ctx->I, ctx->V, tmp, DEFAULT_BLK_SZ);
 123                         hexdump("tmp stage 1: ", tmp, DEFAULT_BLK_SZ);
 124                         output = ctx->rand_data;
 125                         break;
 126                 case 2:
 127                         /*
 128                          * First check that we didn't produce the same
 129                          * random data that we did last time around through this
 130                          */
 131                         if (!memcmp(ctx->rand_data, ctx->last_rand_data,
 132                                         DEFAULT_BLK_SZ)) {
 133                                 if (cont_test) {
 134                                         panic("cprng %p Failed repetition check!\n",
 135                                                 ctx);
 136                                 }
 137
 138                                 printk(KERN_ERR
 139                                         "ctx %p Failed repetition check!\n",
 140                                         ctx);
 141
 142                                 ctx->flags |= PRNG_NEED_RESET;
 143                                 return -EINVAL;
 144                         }
 145                         memcpy(ctx->last_rand_data, ctx->rand_data,
 146                                 DEFAULT_BLK_SZ);
 147
 148                         /*
 149                          * Lastly xor the random data with I
 150                          * and encrypt that to obtain a new secret vector V
 151                          */
 152                         xor_vectors(ctx->rand_data, ctx->I, tmp,
 153                                 DEFAULT_BLK_SZ);
 154                         output = ctx->V;
 155                         hexdump("tmp stage 2: ", tmp, DEFAULT_BLK_SZ);
 156                         break;
 157                 }
 158
 159
 160                 /* do the encryption */
 161                 crypto_cipher_encrypt_one(ctx->tfm, output, tmp);
 162
 163         }
 164
 165         /*
 166          * Now update our DT value
 167          */
 168         for (i = DEFAULT_BLK_SZ - 1; i >= 0; i--) {
 169                 ctx->DT[i] += 1;
 170                 if (ctx->DT[i] != 0)
 171                         break;
 172         }
 173
 174         dbgprint("Returning new block for context %p\n", ctx);
 175         ctx->rand_data_valid = 0;
 176
 177         hexdump("Output DT: ", ctx->DT, DEFAULT_BLK_SZ);
 178         hexdump("Output I: ", ctx->I, DEFAULT_BLK_SZ);
 179         hexdump("Output V: ", ctx->V, DEFAULT_BLK_SZ);
 180         hexdump("New Random Data: ", ctx->rand_data, DEFAULT_BLK_SZ);
 181
 182         return 0;
 183 }
 184
 185 /* Our exported functions */
 186 static int get_prng_bytes(char *buf, size_t nbytes, struct prng_context *ctx,
 187                                 int do_cont_test)
 188 {
 189         unsigned char *ptr = buf;
 190         unsigned int byte_count = (unsigned int)nbytes;
 191         int err;
 192
 193
 194         spin_lock_bh(&ctx->prng_lock);
 195
 196         err = -EINVAL;
 197         if (ctx->flags & PRNG_NEED_RESET)
 198                 goto done;
 199
 200         /*
 201          * If the FIXED_SIZE flag is on, only return whole blocks of
 202          * pseudo random data
 203          */
 204         err = -EINVAL;
 205         if (ctx->flags & PRNG_FIXED_SIZE) {
 206                 if (nbytes < DEFAULT_BLK_SZ)
 207                         goto done;
 208                 byte_count = DEFAULT_BLK_SZ;
 209         }
 210
 211         /*
 212          * Return 0 in case of success as mandated by the kernel
 213          * crypto API interface definition.
 214          */
 215         err = 0;
 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, do_cont_test) < 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                 while (ctx->rand_data_valid < DEFAULT_BLK_SZ) {
 236                         *ptr = ctx->rand_data[ctx->rand_data_valid];
 237                         ptr++;
 238                         byte_count--;
 239                         ctx->rand_data_valid++;
 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, do_cont_test) < 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                               const unsigned char *key, size_t klen,
 283                               const unsigned char *V, const unsigned char *DT)
 284 {
 285         int ret;
 286         const 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,
 355                             const u8 *src, unsigned int slen,
 356                             u8 *rdata, unsigned int dlen)
 357 {
 358         struct prng_context *prng = crypto_rng_ctx(tfm);
 359
 360         return get_prng_bytes(rdata, dlen, prng, 0);
 361 }
 362
 363 /*
 364  *  This is the cprng_registered reset method the seed value is
 365  *  interpreted as the tuple { V KEY DT}
 366  *  V and KEY are required during reset, and DT is optional, detected
 367  *  as being present by testing the length of the seed
 368  */
 369 static int cprng_reset(struct crypto_rng *tfm,
 370                        const u8 *seed, unsigned int slen)
 371 {
 372         struct prng_context *prng = crypto_rng_ctx(tfm);
 373         const u8 *key = seed + DEFAULT_BLK_SZ;
 374         const u8 *dt = NULL;
 375
 376         if (slen < DEFAULT_PRNG_KSZ + DEFAULT_BLK_SZ)
 377                 return -EINVAL;
 378
 379         if (slen >= (2 * DEFAULT_BLK_SZ + DEFAULT_PRNG_KSZ))
 380                 dt = key + DEFAULT_PRNG_KSZ;
 381
 382         reset_prng_context(prng, key, DEFAULT_PRNG_KSZ, seed, dt);
 383
 384         if (prng->flags & PRNG_NEED_RESET)
 385                 return -EINVAL;
 386         return 0;
 387 }
 388
 389 #ifdef CONFIG_CRYPTO_FIPS
 390 static int fips_cprng_get_random(struct crypto_rng *tfm,
 391                                  const u8 *src, unsigned int slen,
 392                                  u8 *rdata, unsigned int dlen)
 393 {
 394         struct prng_context *prng = crypto_rng_ctx(tfm);
 395
 396         return get_prng_bytes(rdata, dlen, prng, 1);
 397 }
 398
 399 static int fips_cprng_reset(struct crypto_rng *tfm,
 400                             const u8 *seed, unsigned int slen)
 401 {
 402         u8 rdata[DEFAULT_BLK_SZ];
 403         const u8 *key = seed + DEFAULT_BLK_SZ;
 404         int rc;
 405
 406         struct prng_context *prng = crypto_rng_ctx(tfm);
 407
 408         if (slen < DEFAULT_PRNG_KSZ + DEFAULT_BLK_SZ)
 409                 return -EINVAL;
 410
 411         /* fips strictly requires seed != key */
 412         if (!memcmp(seed, key, DEFAULT_PRNG_KSZ))
 413                 return -EINVAL;
 414
 415         rc = cprng_reset(tfm, seed, slen);
 416
 417         if (!rc)
 418                 goto out;
 419
 420         /* this primes our continuity test */
 421         rc = get_prng_bytes(rdata, DEFAULT_BLK_SZ, prng, 0);
 422         prng->rand_data_valid = DEFAULT_BLK_SZ;
 423
 424 out:
 425         return rc;
 426 }
 427 #endif
 428
 429 static struct rng_alg rng_algs[] = { {
 430         .generate               = cprng_get_random,
 431         .seed                   = cprng_reset,
 432         .seedsize               = DEFAULT_PRNG_KSZ + 2 * DEFAULT_BLK_SZ,
 433         .base                   =       {
 434                 .cra_name               = "stdrng",
 435                 .cra_driver_name        = "ansi_cprng",
 436                 .cra_priority           = 100,
 437                 .cra_ctxsize            = sizeof(struct prng_context),
 438                 .cra_module             = THIS_MODULE,
 439                 .cra_init               = cprng_init,
 440                 .cra_exit               = cprng_exit,
 441         }
 442 #ifdef CONFIG_CRYPTO_FIPS
 443 }, {
 444         .generate               = fips_cprng_get_random,
 445         .seed                   = fips_cprng_reset,
 446         .seedsize               = DEFAULT_PRNG_KSZ + 2 * DEFAULT_BLK_SZ,
 447         .base                   =       {
 448                 .cra_name               = "fips(ansi_cprng)",
 449                 .cra_driver_name        = "fips_ansi_cprng",
 450                 .cra_priority           = 300,
 451                 .cra_ctxsize            = sizeof(struct prng_context),
 452                 .cra_module             = THIS_MODULE,
 453                 .cra_init               = cprng_init,
 454                 .cra_exit               = cprng_exit,
 455         }
 456 #endif
 457 } };
 458
 459 /* Module initalization */
 460 static int __init prng_mod_init(void)
 461 {
 462         return crypto_register_rngs(rng_algs, ARRAY_SIZE(rng_algs));
 463 }
 464
 465 static void __exit prng_mod_fini(void)
 466 {
 467         crypto_unregister_rngs(rng_algs, ARRAY_SIZE(rng_algs));
 468 }
 469
 470 MODULE_LICENSE("GPL");
 471 MODULE_DESCRIPTION("Software Pseudo Random Number Generator");
 472 MODULE_AUTHOR("Neil Horman <nhorman@tuxdriver.com>");
 473 module_param(dbg, int, 0);
 474 MODULE_PARM_DESC(dbg, "Boolean to enable debugging (0/1 == off/on)");
 475 module_init(prng_mod_init);
 476 module_exit(prng_mod_fini);
 477 MODULE_ALIAS_CRYPTO("stdrng");
 478 MODULE_ALIAS_CRYPTO("ansi_cprng");