crypto/bn/bn_rand.c

   1 /*
   2  * Copyright 1995-2016 The OpenSSL Project Authors. All Rights Reserved.
   3  *
   4  * Licensed under the OpenSSL license (the "License").  You may not use
   5  * this file except in compliance with the License.  You can obtain a copy
   6  * in the file LICENSE in the source distribution or at
   7  * https://www.openssl.org/source/license.html
   8  */
   9
  10 #include <stdio.h>
  11 #include <time.h>
  12 #include "internal/cryptlib.h"
  13 #include "bn_lcl.h"
  14 #include <openssl/rand.h>
  15 #include <openssl/sha.h>
  16
  17 typedef enum bnrand_flag_e {
  18     NORMAL, TESTING, PRIVATE
  19 } BNRAND_FLAG;
  20
  21 static int bnrand(BNRAND_FLAG flag, BIGNUM *rnd, int bits, int top, int bottom)
  22 {
  23     unsigned char *buf = NULL;
  24     int b, ret = 0, bit, bytes, mask;
  25
  26     if (bits == 0) {
  27         if (top != BN_RAND_TOP_ANY || bottom != BN_RAND_BOTTOM_ANY)
  28             goto toosmall;
  29         BN_zero(rnd);
  30         return 1;
  31     }
  32     if (bits < 0 || (bits == 1 && top > 0))
  33         goto toosmall;
  34
  35     bytes = (bits + 7) / 8;
  36     bit = (bits - 1) % 8;
  37     mask = 0xff << (bit + 1);
  38
  39     buf = OPENSSL_malloc(bytes);
  40     if (buf == NULL) {
  41         BNerr(BN_F_BNRAND, ERR_R_MALLOC_FAILURE);
  42         goto err;
  43     }
  44
  45     /* make a random number and set the top and bottom bits */
  46     b = flag == NORMAL ? RAND_bytes(buf, bytes) : RAND_priv_bytes(buf, bytes);
  47     if (b <= 0)
  48         goto err;
  49
  50     if (flag == TESTING) {
  51         /*
  52          * generate patterns that are more likely to trigger BN library bugs
  53          */
  54         int i;
  55         unsigned char c;
  56
  57         for (i = 0; i < bytes; i++) {
  58             if (RAND_bytes(&c, 1) <= 0)
  59                 goto err;
  60             if (c >= 128 && i > 0)
  61                 buf[i] = buf[i - 1];
  62             else if (c < 42)
  63                 buf[i] = 0;
  64             else if (c < 84)
  65                 buf[i] = 255;
  66         }
  67     }
  68
  69     if (top >= 0) {
  70         if (top) {
  71             if (bit == 0) {
  72                 buf[0] = 1;
  73                 buf[1] |= 0x80;
  74             } else {
  75                 buf[0] |= (3 << (bit - 1));
  76             }
  77         } else {
  78             buf[0] |= (1 << bit);
  79         }
  80     }
  81     buf[0] &= ~mask;
  82     if (bottom)                 /* set bottom bit if requested */
  83         buf[bytes - 1] |= 1;
  84     if (!BN_bin2bn(buf, bytes, rnd))
  85         goto err;
  86     ret = 1;
  87  err:
  88     OPENSSL_clear_free(buf, bytes);
  89     bn_check_top(rnd);
  90     return ret;
  91
  92 toosmall:
  93     BNerr(BN_F_BNRAND, BN_R_BITS_TOO_SMALL);
  94     return 0;
  95 }
  96
  97 int BN_rand(BIGNUM *rnd, int bits, int top, int bottom)
  98 {
  99     return bnrand(NORMAL, rnd, bits, top, bottom);
 100 }
 101
 102 int BN_bntest_rand(BIGNUM *rnd, int bits, int top, int bottom)
 103 {
 104     return bnrand(TESTING, rnd, bits, top, bottom);
 105 }
 106
 107 int BN_priv_rand(BIGNUM *rnd, int bits, int top, int bottom)
 108 {
 109     return bnrand(PRIVATE, rnd, bits, top, bottom);
 110 }
 111
 112 /* random number r:  0 <= r < range */
 113 static int bnrand_range(BNRAND_FLAG flag, BIGNUM *r, const BIGNUM *range)
 114 {
 115     int n;
 116     int count = 100;
 117
 118     if (range->neg || BN_is_zero(range)) {
 119         BNerr(BN_F_BNRAND_RANGE, BN_R_INVALID_RANGE);
 120         return 0;
 121     }
 122
 123     n = BN_num_bits(range);     /* n > 0 */
 124
 125     /* BN_is_bit_set(range, n - 1) always holds */
 126
 127     if (n == 1)
 128         BN_zero(r);
 129     else if (!BN_is_bit_set(range, n - 2) && !BN_is_bit_set(range, n - 3)) {
 130         /*
 131          * range = 100..._2, so 3*range (= 11..._2) is exactly one bit longer
 132          * than range
 133          */
 134         do {
 135             if (!bnrand(flag, r, n + 1, BN_RAND_TOP_ANY, BN_RAND_BOTTOM_ANY))
 136                 return 0;
 137
 138             /*
 139              * If r < 3*range, use r := r MOD range (which is either r, r -
 140              * range, or r - 2*range). Otherwise, iterate once more. Since
 141              * 3*range = 11..._2, each iteration succeeds with probability >=
 142              * .75.
 143              */
 144             if (BN_cmp(r, range) >= 0) {
 145                 if (!BN_sub(r, r, range))
 146                     return 0;
 147                 if (BN_cmp(r, range) >= 0)
 148                     if (!BN_sub(r, r, range))
 149                         return 0;
 150             }
 151
 152             if (!--count) {
 153                 BNerr(BN_F_BNRAND_RANGE, BN_R_TOO_MANY_ITERATIONS);
 154                 return 0;
 155             }
 156
 157         }
 158         while (BN_cmp(r, range) >= 0);
 159     } else {
 160         do {
 161             /* range = 11..._2  or  range = 101..._2 */
 162             if (!bnrand(flag, r, n, BN_RAND_TOP_ANY, BN_RAND_BOTTOM_ANY))
 163                 return 0;
 164
 165             if (!--count) {
 166                 BNerr(BN_F_BNRAND_RANGE, BN_R_TOO_MANY_ITERATIONS);
 167                 return 0;
 168             }
 169         }
 170         while (BN_cmp(r, range) >= 0);
 171     }
 172
 173     bn_check_top(r);
 174     return 1;
 175 }
 176
 177 int BN_rand_range(BIGNUM *r, const BIGNUM *range)
 178 {
 179     return bnrand_range(NORMAL, r, range);
 180 }
 181
 182 int BN_priv_rand_range(BIGNUM *r, const BIGNUM *range)
 183 {
 184     return bnrand_range(PRIVATE, r, range);
 185 }
 186
 187 int BN_pseudo_rand(BIGNUM *rnd, int bits, int top, int bottom)
 188 {
 189     return BN_rand(rnd, bits, top, bottom);
 190 }
 191
 192 int BN_pseudo_rand_range(BIGNUM *r, const BIGNUM *range)
 193 {
 194     return BN_rand_range(r, range);
 195 }
 196
 197 /*
 198  * BN_generate_dsa_nonce generates a random number 0 <= out < range. Unlike
 199  * BN_rand_range, it also includes the contents of |priv| and |message| in
 200  * the generation so that an RNG failure isn't fatal as long as |priv|
 201  * remains secret. This is intended for use in DSA and ECDSA where an RNG
 202  * weakness leads directly to private key exposure unless this function is
 203  * used.
 204  */
 205 int BN_generate_dsa_nonce(BIGNUM *out, const BIGNUM *range,
 206                           const BIGNUM *priv, const unsigned char *message,
 207                           size_t message_len, BN_CTX *ctx)
 208 {
 209     SHA512_CTX sha;
 210     /*
 211      * We use 512 bits of random data per iteration to ensure that we have at
 212      * least |range| bits of randomness.
 213      */
 214     unsigned char random_bytes[64];
 215     unsigned char digest[SHA512_DIGEST_LENGTH];
 216     unsigned done, todo;
 217     /* We generate |range|+8 bytes of random output. */
 218     const unsigned num_k_bytes = BN_num_bytes(range) + 8;
 219     unsigned char private_bytes[96];
 220     unsigned char *k_bytes;
 221     int ret = 0;
 222
 223     k_bytes = OPENSSL_malloc(num_k_bytes);
 224     if (k_bytes == NULL)
 225         goto err;
 226
 227     /* We copy |priv| into a local buffer to avoid exposing its length. */
 228     todo = sizeof(priv->d[0]) * priv->top;
 229     if (todo > sizeof(private_bytes)) {
 230         /*
 231          * No reasonable DSA or ECDSA key should have a private key this
 232          * large and we don't handle this case in order to avoid leaking the
 233          * length of the private key.
 234          */
 235         BNerr(BN_F_BN_GENERATE_DSA_NONCE, BN_R_PRIVATE_KEY_TOO_LARGE);
 236         goto err;
 237     }
 238     memcpy(private_bytes, priv->d, todo);
 239     memset(private_bytes + todo, 0, sizeof(private_bytes) - todo);
 240
 241     for (done = 0; done < num_k_bytes;) {
 242         if (RAND_bytes(random_bytes, sizeof(random_bytes)) != 1)
 243             goto err;
 244         SHA512_Init(&sha);
 245         SHA512_Update(&sha, &done, sizeof(done));
 246         SHA512_Update(&sha, private_bytes, sizeof(private_bytes));
 247         SHA512_Update(&sha, message, message_len);
 248         SHA512_Update(&sha, random_bytes, sizeof(random_bytes));
 249         SHA512_Final(digest, &sha);
 250
 251         todo = num_k_bytes - done;
 252         if (todo > SHA512_DIGEST_LENGTH)
 253             todo = SHA512_DIGEST_LENGTH;
 254         memcpy(k_bytes + done, digest, todo);
 255         done += todo;
 256     }
 257
 258     if (!BN_bin2bn(k_bytes, num_k_bytes, out))
 259         goto err;
 260     if (BN_mod(out, out, range, ctx) != 1)
 261         goto err;
 262     ret = 1;
 263
 264  err:
 265     OPENSSL_free(k_bytes);
 266     OPENSSL_cleanse(private_bytes, sizeof(private_bytes));
 267     return ret;
 268 }