crypto/bn/bn_rand.c

   1 /*
   2  * Copyright 1995-2021 The OpenSSL Project Authors. All Rights Reserved.
   3  *
   4  * Licensed under the Apache License 2.0 (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 "crypto/rand.h"
  14 #include "bn_local.h"
  15 #include <openssl/rand.h>
  16 #include <openssl/sha.h>
  17 #include <openssl/evp.h>
  18
  19 typedef enum bnrand_flag_e {
  20     NORMAL, TESTING, PRIVATE
  21 } BNRAND_FLAG;
  22
  23 static int bnrand(BNRAND_FLAG flag, BIGNUM *rnd, int bits, int top, int bottom,
  24                   unsigned int strength, BN_CTX *ctx)
  25 {
  26     unsigned char *buf = NULL;
  27     int b, ret = 0, bit, bytes, mask;
  28     OSSL_LIB_CTX *libctx = ossl_bn_get_libctx(ctx);
  29
  30     if (bits == 0) {
  31         if (top != BN_RAND_TOP_ANY || bottom != BN_RAND_BOTTOM_ANY)
  32             goto toosmall;
  33         BN_zero(rnd);
  34         return 1;
  35     }
  36     if (bits < 0 || (bits == 1 && top > 0))
  37         goto toosmall;
  38
  39     bytes = (bits + 7) / 8;
  40     bit = (bits - 1) % 8;
  41     mask = 0xff << (bit + 1);
  42
  43     buf = OPENSSL_malloc(bytes);
  44     if (buf == NULL)
  45         goto err;
  46
  47     /* make a random number and set the top and bottom bits */
  48     b = flag == NORMAL ? RAND_bytes_ex(libctx, buf, bytes, strength)
  49                        : RAND_priv_bytes_ex(libctx, buf, bytes, strength);
  50     if (b <= 0)
  51         goto err;
  52
  53     if (flag == TESTING) {
  54         /*
  55          * generate patterns that are more likely to trigger BN library bugs
  56          */
  57         int i;
  58         unsigned char c;
  59
  60         for (i = 0; i < bytes; i++) {
  61             if (RAND_bytes_ex(libctx, &c, 1, strength) <= 0)
  62                 goto err;
  63             if (c >= 128 && i > 0)
  64                 buf[i] = buf[i - 1];
  65             else if (c < 42)
  66                 buf[i] = 0;
  67             else if (c < 84)
  68                 buf[i] = 255;
  69         }
  70     }
  71
  72     if (top >= 0) {
  73         if (top) {
  74             if (bit == 0) {
  75                 buf[0] = 1;
  76                 buf[1] |= 0x80;
  77             } else {
  78                 buf[0] |= (3 << (bit - 1));
  79             }
  80         } else {
  81             buf[0] |= (1 << bit);
  82         }
  83     }
  84     buf[0] &= ~mask;
  85     if (bottom)                 /* set bottom bit if requested */
  86         buf[bytes - 1] |= 1;
  87     if (!BN_bin2bn(buf, bytes, rnd))
  88         goto err;
  89     ret = 1;
  90  err:
  91     OPENSSL_clear_free(buf, bytes);
  92     bn_check_top(rnd);
  93     return ret;
  94
  95 toosmall:
  96     ERR_raise(ERR_LIB_BN, BN_R_BITS_TOO_SMALL);
  97     return 0;
  98 }
  99
 100 int BN_rand_ex(BIGNUM *rnd, int bits, int top, int bottom,
 101                unsigned int strength, BN_CTX *ctx)
 102 {
 103     return bnrand(NORMAL, rnd, bits, top, bottom, strength, ctx);
 104 }
 105 #ifndef FIPS_MODULE
 106 int BN_rand(BIGNUM *rnd, int bits, int top, int bottom)
 107 {
 108     return bnrand(NORMAL, rnd, bits, top, bottom, 0, NULL);
 109 }
 110
 111 int BN_bntest_rand(BIGNUM *rnd, int bits, int top, int bottom)
 112 {
 113     return bnrand(TESTING, rnd, bits, top, bottom, 0, NULL);
 114 }
 115 #endif
 116
 117 int BN_priv_rand_ex(BIGNUM *rnd, int bits, int top, int bottom,
 118                     unsigned int strength, BN_CTX *ctx)
 119 {
 120     return bnrand(PRIVATE, rnd, bits, top, bottom, strength, ctx);
 121 }
 122
 123 #ifndef FIPS_MODULE
 124 int BN_priv_rand(BIGNUM *rnd, int bits, int top, int bottom)
 125 {
 126     return bnrand(PRIVATE, rnd, bits, top, bottom, 0, NULL);
 127 }
 128 #endif
 129
 130 /* random number r:  0 <= r < range */
 131 static int bnrand_range(BNRAND_FLAG flag, BIGNUM *r, const BIGNUM *range,
 132                         unsigned int strength, BN_CTX *ctx)
 133 {
 134     int n;
 135     int count = 100;
 136
 137     if (r == NULL) {
 138         ERR_raise(ERR_LIB_BN, ERR_R_PASSED_NULL_PARAMETER);
 139         return 0;
 140     }
 141
 142     if (range->neg || BN_is_zero(range)) {
 143         ERR_raise(ERR_LIB_BN, BN_R_INVALID_RANGE);
 144         return 0;
 145     }
 146
 147     n = BN_num_bits(range);     /* n > 0 */
 148
 149     /* BN_is_bit_set(range, n - 1) always holds */
 150
 151     if (n == 1)
 152         BN_zero(r);
 153     else if (!BN_is_bit_set(range, n - 2) && !BN_is_bit_set(range, n - 3)) {
 154         /*
 155          * range = 100..._2, so 3*range (= 11..._2) is exactly one bit longer
 156          * than range
 157          */
 158         do {
 159             if (!bnrand(flag, r, n + 1, BN_RAND_TOP_ANY, BN_RAND_BOTTOM_ANY,
 160                         strength, ctx))
 161                 return 0;
 162
 163             /*
 164              * If r < 3*range, use r := r MOD range (which is either r, r -
 165              * range, or r - 2*range). Otherwise, iterate once more. Since
 166              * 3*range = 11..._2, each iteration succeeds with probability >=
 167              * .75.
 168              */
 169             if (BN_cmp(r, range) >= 0) {
 170                 if (!BN_sub(r, r, range))
 171                     return 0;
 172                 if (BN_cmp(r, range) >= 0)
 173                     if (!BN_sub(r, r, range))
 174                         return 0;
 175             }
 176
 177             if (!--count) {
 178                 ERR_raise(ERR_LIB_BN, BN_R_TOO_MANY_ITERATIONS);
 179                 return 0;
 180             }
 181
 182         }
 183         while (BN_cmp(r, range) >= 0);
 184     } else {
 185         do {
 186             /* range = 11..._2  or  range = 101..._2 */
 187             if (!bnrand(flag, r, n, BN_RAND_TOP_ANY, BN_RAND_BOTTOM_ANY, 0,
 188                         ctx))
 189                 return 0;
 190
 191             if (!--count) {
 192                 ERR_raise(ERR_LIB_BN, BN_R_TOO_MANY_ITERATIONS);
 193                 return 0;
 194             }
 195         }
 196         while (BN_cmp(r, range) >= 0);
 197     }
 198
 199     bn_check_top(r);
 200     return 1;
 201 }
 202
 203 int BN_rand_range_ex(BIGNUM *r, const BIGNUM *range, unsigned int strength,
 204                      BN_CTX *ctx)
 205 {
 206     return bnrand_range(NORMAL, r, range, strength, ctx);
 207 }
 208
 209 #ifndef FIPS_MODULE
 210 int BN_rand_range(BIGNUM *r, const BIGNUM *range)
 211 {
 212     return bnrand_range(NORMAL, r, range, 0, NULL);
 213 }
 214 #endif
 215
 216 int BN_priv_rand_range_ex(BIGNUM *r, const BIGNUM *range, unsigned int strength,
 217                           BN_CTX *ctx)
 218 {
 219     return bnrand_range(PRIVATE, r, range, strength, ctx);
 220 }
 221
 222 #ifndef FIPS_MODULE
 223 int BN_priv_rand_range(BIGNUM *r, const BIGNUM *range)
 224 {
 225     return bnrand_range(PRIVATE, r, range, 0, NULL);
 226 }
 227
 228 # ifndef OPENSSL_NO_DEPRECATED_3_0
 229 int BN_pseudo_rand(BIGNUM *rnd, int bits, int top, int bottom)
 230 {
 231     return BN_rand(rnd, bits, top, bottom);
 232 }
 233
 234 int BN_pseudo_rand_range(BIGNUM *r, const BIGNUM *range)
 235 {
 236     return BN_rand_range(r, range);
 237 }
 238 # endif
 239 #endif
 240
 241 /*
 242  * BN_generate_dsa_nonce generates a random number 0 <= out < range. Unlike
 243  * BN_rand_range, it also includes the contents of |priv| and |message| in
 244  * the generation so that an RNG failure isn't fatal as long as |priv|
 245  * remains secret. This is intended for use in DSA and ECDSA where an RNG
 246  * weakness leads directly to private key exposure unless this function is
 247  * used.
 248  */
 249 int BN_generate_dsa_nonce(BIGNUM *out, const BIGNUM *range,
 250                           const BIGNUM *priv, const unsigned char *message,
 251                           size_t message_len, BN_CTX *ctx)
 252 {
 253     EVP_MD_CTX *mdctx = EVP_MD_CTX_new();
 254     /*
 255      * We use 512 bits of random data per iteration to ensure that we have at
 256      * least |range| bits of randomness.
 257      */
 258     unsigned char random_bytes[64];
 259     unsigned char digest[SHA512_DIGEST_LENGTH];
 260     unsigned done, todo;
 261     /* We generate |range|+8 bytes of random output. */
 262     const unsigned num_k_bytes = BN_num_bytes(range) + 8;
 263     unsigned char private_bytes[96];
 264     unsigned char *k_bytes = NULL;
 265     int ret = 0;
 266     EVP_MD *md = NULL;
 267     OSSL_LIB_CTX *libctx = ossl_bn_get_libctx(ctx);
 268
 269     if (mdctx == NULL)
 270         goto err;
 271
 272     k_bytes = OPENSSL_malloc(num_k_bytes);
 273     if (k_bytes == NULL)
 274         goto err;
 275
 276     /* We copy |priv| into a local buffer to avoid exposing its length. */
 277     if (BN_bn2binpad(priv, private_bytes, sizeof(private_bytes)) < 0) {
 278         /*
 279          * No reasonable DSA or ECDSA key should have a private key this
 280          * large and we don't handle this case in order to avoid leaking the
 281          * length of the private key.
 282          */
 283         ERR_raise(ERR_LIB_BN, BN_R_PRIVATE_KEY_TOO_LARGE);
 284         goto err;
 285     }
 286
 287     md = EVP_MD_fetch(libctx, "SHA512", NULL);
 288     if (md == NULL) {
 289         ERR_raise(ERR_LIB_BN, BN_R_NO_SUITABLE_DIGEST);
 290         goto err;
 291     }
 292     for (done = 0; done < num_k_bytes;) {
 293         if (RAND_priv_bytes_ex(libctx, random_bytes, sizeof(random_bytes), 0) <= 0)
 294             goto err;
 295
 296         if (!EVP_DigestInit_ex(mdctx, md, NULL)
 297                 || !EVP_DigestUpdate(mdctx, &done, sizeof(done))
 298                 || !EVP_DigestUpdate(mdctx, private_bytes,
 299                                      sizeof(private_bytes))
 300                 || !EVP_DigestUpdate(mdctx, message, message_len)
 301                 || !EVP_DigestUpdate(mdctx, random_bytes, sizeof(random_bytes))
 302                 || !EVP_DigestFinal_ex(mdctx, digest, NULL))
 303             goto err;
 304
 305         todo = num_k_bytes - done;
 306         if (todo > SHA512_DIGEST_LENGTH)
 307             todo = SHA512_DIGEST_LENGTH;
 308         memcpy(k_bytes + done, digest, todo);
 309         done += todo;
 310     }
 311
 312     if (!BN_bin2bn(k_bytes, num_k_bytes, out))
 313         goto err;
 314     if (BN_mod(out, out, range, ctx) != 1)
 315         goto err;
 316     ret = 1;
 317
 318  err:
 319     EVP_MD_CTX_free(mdctx);
 320     EVP_MD_free(md);
 321     OPENSSL_free(k_bytes);
 322     OPENSSL_cleanse(private_bytes, sizeof(private_bytes));
 323     return ret;
 324 }