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 
   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                 for (; ctx->rand_data_valid < DEFAULT_BLK_SZ;
  234                         ctx->rand_data_valid++) {
  235                         *ptr = ctx->rand_data[ctx->rand_data_valid];
  236                         ptr++;
  237                         byte_count--;
  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");
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FreeBSD/Linux Kernel Cross Reference sys/crypto/ansi_cprng.c

FreeBSD/Linux Kernel Cross Reference
sys/crypto/ansi_cprng.c
