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 #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");