linux/crypto/ansi_cprng.c
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   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
  46struct 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
  58static int dbg;
  59
  60static 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 {\
  71if (dbg)\
  72        printk(format, ##args);\
  73} while (0)
  74
  75static 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 */
  88static 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 */
 188static int get_prng_bytes(char *buf, size_t nbytes, struct prng_context *ctx)
 189{
 190        unsigned long flags;
 191        unsigned char *ptr = buf;
 192        unsigned int byte_count = (unsigned int)nbytes;
 193        int err;
 194
 195
 196        if (nbytes < 0)
 197                return -EINVAL;
 198
 199        spin_lock_irqsave(&ctx->prng_lock, flags);
 200
 201        err = -EINVAL;
 202        if (ctx->flags & PRNG_NEED_RESET)
 203                goto done;
 204
 205        /*
 206         * If the FIXED_SIZE flag is on, only return whole blocks of
 207         * pseudo random data
 208         */
 209        err = -EINVAL;
 210        if (ctx->flags & PRNG_FIXED_SIZE) {
 211                if (nbytes < DEFAULT_BLK_SZ)
 212                        goto done;
 213                byte_count = DEFAULT_BLK_SZ;
 214        }
 215
 216        err = byte_count;
 217
 218        dbgprint(KERN_CRIT "getting %d random bytes for context %p\n",
 219                byte_count, ctx);
 220
 221
 222remainder:
 223        if (ctx->rand_data_valid == DEFAULT_BLK_SZ) {
 224                if (_get_more_prng_bytes(ctx) < 0) {
 225                        memset(buf, 0, nbytes);
 226                        err = -EINVAL;
 227                        goto done;
 228                }
 229        }
 230
 231        /*
 232         * Copy any data less than an entire block
 233         */
 234        if (byte_count < DEFAULT_BLK_SZ) {
 235empty_rbuf:
 236                for (; ctx->rand_data_valid < DEFAULT_BLK_SZ;
 237                        ctx->rand_data_valid++) {
 238                        *ptr = ctx->rand_data[ctx->rand_data_valid];
 239                        ptr++;
 240                        byte_count--;
 241                        if (byte_count == 0)
 242                                goto done;
 243                }
 244        }
 245
 246        /*
 247         * Now copy whole blocks
 248         */
 249        for (; byte_count >= DEFAULT_BLK_SZ; byte_count -= DEFAULT_BLK_SZ) {
 250                if (ctx->rand_data_valid == DEFAULT_BLK_SZ) {
 251                        if (_get_more_prng_bytes(ctx) < 0) {
 252                                memset(buf, 0, nbytes);
 253                                err = -EINVAL;
 254                                goto done;
 255                        }
 256                }
 257                if (ctx->rand_data_valid > 0)
 258                        goto empty_rbuf;
 259                memcpy(ptr, ctx->rand_data, DEFAULT_BLK_SZ);
 260                ctx->rand_data_valid += DEFAULT_BLK_SZ;
 261                ptr += DEFAULT_BLK_SZ;
 262        }
 263
 264        /*
 265         * Now go back and get any remaining partial block
 266         */
 267        if (byte_count)
 268                goto remainder;
 269
 270done:
 271        spin_unlock_irqrestore(&ctx->prng_lock, flags);
 272        dbgprint(KERN_CRIT "returning %d from get_prng_bytes in context %p\n",
 273                err, ctx);
 274        return err;
 275}
 276
 277static void free_prng_context(struct prng_context *ctx)
 278{
 279        crypto_free_cipher(ctx->tfm);
 280}
 281
 282static int reset_prng_context(struct prng_context *ctx,
 283                              unsigned char *key, size_t klen,
 284                              unsigned char *V, unsigned char *DT)
 285{
 286        int ret;
 287        int rc = -EINVAL;
 288        unsigned char *prng_key;
 289
 290        spin_lock(&ctx->prng_lock);
 291        ctx->flags |= PRNG_NEED_RESET;
 292
 293        prng_key = (key != NULL) ? key : (unsigned char *)DEFAULT_PRNG_KEY;
 294
 295        if (!key)
 296                klen = DEFAULT_PRNG_KSZ;
 297
 298        if (V)
 299                memcpy(ctx->V, V, DEFAULT_BLK_SZ);
 300        else
 301                memcpy(ctx->V, DEFAULT_V_SEED, DEFAULT_BLK_SZ);
 302
 303        if (DT)
 304                memcpy(ctx->DT, DT, DEFAULT_BLK_SZ);
 305        else
 306                memset(ctx->DT, 0, DEFAULT_BLK_SZ);
 307
 308        memset(ctx->rand_data, 0, DEFAULT_BLK_SZ);
 309        memset(ctx->last_rand_data, 0, DEFAULT_BLK_SZ);
 310
 311        if (ctx->tfm)
 312                crypto_free_cipher(ctx->tfm);
 313
 314        ctx->tfm = crypto_alloc_cipher("aes", 0, 0);
 315        if (IS_ERR(ctx->tfm)) {
 316                dbgprint(KERN_CRIT "Failed to alloc tfm for context %p\n",
 317                        ctx);
 318                ctx->tfm = NULL;
 319                goto out;
 320        }
 321
 322        ctx->rand_data_valid = DEFAULT_BLK_SZ;
 323
 324        ret = crypto_cipher_setkey(ctx->tfm, prng_key, klen);
 325        if (ret) {
 326                dbgprint(KERN_CRIT "PRNG: setkey() failed flags=%x\n",
 327                        crypto_cipher_get_flags(ctx->tfm));
 328                crypto_free_cipher(ctx->tfm);
 329                goto out;
 330        }
 331
 332        rc = 0;
 333        ctx->flags &= ~PRNG_NEED_RESET;
 334out:
 335        spin_unlock(&ctx->prng_lock);
 336
 337        return rc;
 338
 339}
 340
 341static int cprng_init(struct crypto_tfm *tfm)
 342{
 343        struct prng_context *ctx = crypto_tfm_ctx(tfm);
 344
 345        spin_lock_init(&ctx->prng_lock);
 346
 347        if (reset_prng_context(ctx, NULL, DEFAULT_PRNG_KSZ, NULL, NULL) < 0)
 348                return -EINVAL;
 349
 350        /*
 351         * after allocation, we should always force the user to reset
 352         * so they don't inadvertently use the insecure default values
 353         * without specifying them intentially
 354         */
 355        ctx->flags |= PRNG_NEED_RESET;
 356        return 0;
 357}
 358
 359static void cprng_exit(struct crypto_tfm *tfm)
 360{
 361        free_prng_context(crypto_tfm_ctx(tfm));
 362}
 363
 364static int cprng_get_random(struct crypto_rng *tfm, u8 *rdata,
 365                            unsigned int dlen)
 366{
 367        struct prng_context *prng = crypto_rng_ctx(tfm);
 368
 369        return get_prng_bytes(rdata, dlen, prng);
 370}
 371
 372/*
 373 *  This is the cprng_registered reset method the seed value is
 374 *  interpreted as the tuple { V KEY DT}
 375 *  V and KEY are required during reset, and DT is optional, detected
 376 *  as being present by testing the length of the seed
 377 */
 378static int cprng_reset(struct crypto_rng *tfm, u8 *seed, unsigned int slen)
 379{
 380        struct prng_context *prng = crypto_rng_ctx(tfm);
 381        u8 *key = seed + DEFAULT_BLK_SZ;
 382        u8 *dt = NULL;
 383
 384        if (slen < DEFAULT_PRNG_KSZ + DEFAULT_BLK_SZ)
 385                return -EINVAL;
 386
 387        if (slen >= (2 * DEFAULT_BLK_SZ + DEFAULT_PRNG_KSZ))
 388                dt = key + DEFAULT_PRNG_KSZ;
 389
 390        reset_prng_context(prng, key, DEFAULT_PRNG_KSZ, seed, dt);
 391
 392        if (prng->flags & PRNG_NEED_RESET)
 393                return -EINVAL;
 394        return 0;
 395}
 396
 397static struct crypto_alg rng_alg = {
 398        .cra_name               = "stdrng",
 399        .cra_driver_name        = "ansi_cprng",
 400        .cra_priority           = 100,
 401        .cra_flags              = CRYPTO_ALG_TYPE_RNG,
 402        .cra_ctxsize            = sizeof(struct prng_context),
 403        .cra_type               = &crypto_rng_type,
 404        .cra_module             = THIS_MODULE,
 405        .cra_list               = LIST_HEAD_INIT(rng_alg.cra_list),
 406        .cra_init               = cprng_init,
 407        .cra_exit               = cprng_exit,
 408        .cra_u                  = {
 409                .rng = {
 410                        .rng_make_random        = cprng_get_random,
 411                        .rng_reset              = cprng_reset,
 412                        .seedsize = DEFAULT_PRNG_KSZ + 2*DEFAULT_BLK_SZ,
 413                }
 414        }
 415};
 416
 417
 418/* Module initalization */
 419static int __init prng_mod_init(void)
 420{
 421        int ret = 0;
 422
 423        if (fips_enabled)
 424                rng_alg.cra_priority += 200;
 425
 426        ret = crypto_register_alg(&rng_alg);
 427
 428        if (ret)
 429                goto out;
 430out:
 431        return 0;
 432}
 433
 434static void __exit prng_mod_fini(void)
 435{
 436        crypto_unregister_alg(&rng_alg);
 437        return;
 438}
 439
 440MODULE_LICENSE("GPL");
 441MODULE_DESCRIPTION("Software Pseudo Random Number Generator");
 442MODULE_AUTHOR("Neil Horman <nhorman@tuxdriver.com>");
 443module_param(dbg, int, 0);
 444MODULE_PARM_DESC(dbg, "Boolean to enable debugging (0/1 == off/on)");
 445module_init(prng_mod_init);
 446module_exit(prng_mod_fini);
 447MODULE_ALIAS("stdrng");
 448