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 static int bnrand(int testing, BIGNUM *rnd, int bits, int top, int bottom)
  18 {
  19     unsigned char *buf = NULL;
  20     int ret = 0, bit, bytes, mask;
  21     time_t tim;
  22
  23     if (bits == 0) {
  24         if (top != BN_RAND_TOP_ANY || bottom != BN_RAND_BOTTOM_ANY)
  25             goto toosmall;
  26         BN_zero(rnd);
  27         return 1;
  28     }
  29     if (bits < 0 || (bits == 1 && top > 0))
  30         goto toosmall;
  31
  32     bytes = (bits + 7) / 8;
  33     bit = (bits - 1) % 8;
  34     mask = 0xff << (bit + 1);
  35
  36     buf = OPENSSL_malloc(bytes);
  37     if (buf == NULL) {
  38         BNerr(BN_F_BNRAND, ERR_R_MALLOC_FAILURE);
  39         goto err;
  40     }
  41
  42     /* make a random number and set the top and bottom bits */
  43     time(&tim);
  44     RAND_add(&tim, sizeof(tim), 0.0);
  45
  46     if (RAND_bytes(buf, bytes) <= 0)
  47         goto err;
  48
  49     if (testing) {
  50         /*
  51          * generate patterns that are more likely to trigger BN library bugs
  52          */
  53         int i;
  54         unsigned char c;
  55
  56         for (i = 0; i < bytes; i++) {
  57             if (RAND_bytes(&c, 1) <= 0)
  58                 goto err;
  59             if (c >= 128 && i > 0)
  60                 buf[i] = buf[i - 1];
  61             else if (c < 42)
  62                 buf[i] = 0;
  63             else if (c < 84)
  64                 buf[i] = 255;
  65         }
  66     }
  67
  68     if (top >= 0) {
  69         if (top) {
  70             if (bit == 0) {
  71                 buf[0] = 1;
  72                 buf[1] |= 0x80;
  73             } else {
  74                 buf[0] |= (3 << (bit - 1));
  75             }
  76         } else {
  77             buf[0] |= (1 << bit);
  78         }
  79     }
  80     buf[0] &= ~mask;
  81     if (bottom)                 /* set bottom bit if requested */
  82         buf[bytes - 1] |= 1;
  83     if (!BN_bin2bn(buf, bytes, rnd))
  84         goto err;
  85     ret = 1;
  86  err:
  87     OPENSSL_clear_free(buf, bytes);
  88     bn_check_top(rnd);
  89     return (ret);
  90
  91 toosmall:
  92     BNerr(BN_F_BNRAND, BN_R_BITS_TOO_SMALL);
  93     return 0;
  94 }
  95
  96 int BN_rand(BIGNUM *rnd, int bits, int top, int bottom)
  97 {
  98     return bnrand(0, rnd, bits, top, bottom);
  99 }
 100
 101 int BN_bntest_rand(BIGNUM *rnd, int bits, int top, int bottom)
 102 {
 103     return bnrand(1, rnd, bits, top, bottom);
 104 }
 105
 106 /* random number r:  0 <= r < range */
 107 int BN_rand_range(BIGNUM *r, const BIGNUM *range)
 108 {
 109     int n;
 110     int count = 100;
 111
 112     if (range->neg || BN_is_zero(range)) {
 113         BNerr(BN_F_BN_RAND_RANGE, BN_R_INVALID_RANGE);
 114         return 0;
 115     }
 116
 117     n = BN_num_bits(range);     /* n > 0 */
 118
 119     /* BN_is_bit_set(range, n - 1) always holds */
 120
 121     if (n == 1)
 122         BN_zero(r);
 123     else if (!BN_is_bit_set(range, n - 2) && !BN_is_bit_set(range, n - 3)) {
 124         /*
 125          * range = 100..._2, so 3*range (= 11..._2) is exactly one bit longer
 126          * than range
 127          */
 128         do {
 129             if (!BN_rand(r, n + 1, BN_RAND_TOP_ANY, BN_RAND_BOTTOM_ANY))
 130                 return 0;
 131             /*
 132              * If r < 3*range, use r := r MOD range (which is either r, r -
 133              * range, or r - 2*range). Otherwise, iterate once more. Since
 134              * 3*range = 11..._2, each iteration succeeds with probability >=
 135              * .75.
 136              */
 137             if (BN_cmp(r, range) >= 0) {
 138                 if (!BN_sub(r, r, range))
 139                     return 0;
 140                 if (BN_cmp(r, range) >= 0)
 141                     if (!BN_sub(r, r, range))
 142                         return 0;
 143             }
 144
 145             if (!--count) {
 146                 BNerr(BN_F_BN_RAND_RANGE, BN_R_TOO_MANY_ITERATIONS);
 147                 return 0;
 148             }
 149
 150         }
 151         while (BN_cmp(r, range) >= 0);
 152     } else {
 153         do {
 154             /* range = 11..._2  or  range = 101..._2 */
 155             if (!BN_rand(r, n, BN_RAND_TOP_ANY, BN_RAND_BOTTOM_ANY))
 156                 return 0;
 157
 158             if (!--count) {
 159                 BNerr(BN_F_BN_RAND_RANGE, BN_R_TOO_MANY_ITERATIONS);
 160                 return 0;
 161             }
 162         }
 163         while (BN_cmp(r, range) >= 0);
 164     }
 165
 166     bn_check_top(r);
 167     return 1;
 168 }
 169
 170 int BN_pseudo_rand(BIGNUM *rnd, int bits, int top, int bottom)
 171 {
 172     return BN_rand(rnd, bits, top, bottom);
 173 }
 174
 175 int BN_pseudo_rand_range(BIGNUM *r, const BIGNUM *range)
 176 {
 177     return BN_rand_range(r, range);
 178 }
 179
 180 /*
 181  * BN_generate_dsa_nonce generates a random number 0 <= out < range. Unlike
 182  * BN_rand_range, it also includes the contents of |priv| and |message| in
 183  * the generation so that an RNG failure isn't fatal as long as |priv|
 184  * remains secret. This is intended for use in DSA and ECDSA where an RNG
 185  * weakness leads directly to private key exposure unless this function is
 186  * used.
 187  */
 188 int BN_generate_dsa_nonce(BIGNUM *out, const BIGNUM *range,
 189                           const BIGNUM *priv, const unsigned char *message,
 190                           size_t message_len, BN_CTX *ctx)
 191 {
 192     SHA512_CTX sha;
 193     /*
 194      * We use 512 bits of random data per iteration to ensure that we have at
 195      * least |range| bits of randomness.
 196      */
 197     unsigned char random_bytes[64];
 198     unsigned char digest[SHA512_DIGEST_LENGTH];
 199     unsigned done, todo;
 200     /* We generate |range|+8 bytes of random output. */
 201     const unsigned num_k_bytes = BN_num_bytes(range) + 8;
 202     unsigned char private_bytes[96];
 203     unsigned char *k_bytes;
 204     int ret = 0;
 205
 206     k_bytes = OPENSSL_malloc(num_k_bytes);
 207     if (k_bytes == NULL)
 208         goto err;
 209
 210     /* We copy |priv| into a local buffer to avoid exposing its length. */
 211     todo = sizeof(priv->d[0]) * priv->top;
 212     if (todo > sizeof(private_bytes)) {
 213         /*
 214          * No reasonable DSA or ECDSA key should have a private key this
 215          * large and we don't handle this case in order to avoid leaking the
 216          * length of the private key.
 217          */
 218         BNerr(BN_F_BN_GENERATE_DSA_NONCE, BN_R_PRIVATE_KEY_TOO_LARGE);
 219         goto err;
 220     }
 221     memcpy(private_bytes, priv->d, todo);
 222     memset(private_bytes + todo, 0, sizeof(private_bytes) - todo);
 223
 224     for (done = 0; done < num_k_bytes;) {
 225         if (RAND_bytes(random_bytes, sizeof(random_bytes)) != 1)
 226             goto err;
 227         SHA512_Init(&sha);
 228         SHA512_Update(&sha, &done, sizeof(done));
 229         SHA512_Update(&sha, private_bytes, sizeof(private_bytes));
 230         SHA512_Update(&sha, message, message_len);
 231         SHA512_Update(&sha, random_bytes, sizeof(random_bytes));
 232         SHA512_Final(digest, &sha);
 233
 234         todo = num_k_bytes - done;
 235         if (todo > SHA512_DIGEST_LENGTH)
 236             todo = SHA512_DIGEST_LENGTH;
 237         memcpy(k_bytes + done, digest, todo);
 238         done += todo;
 239     }
 240
 241     if (!BN_bin2bn(k_bytes, num_k_bytes, out))
 242         goto err;
 243     if (BN_mod(out, out, range, ctx) != 1)
 244         goto err;
 245     ret = 1;
 246
 247  err:
 248     OPENSSL_free(k_bytes);
 249     OPENSSL_cleanse(private_bytes, sizeof(private_bytes));
 250     return ret;
 251 }