crypto/dh/dh_key.c

   1 /* crypto/dh/dh_key.c */
   2 /* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
   3  * All rights reserved.
   4  *
   5  * This package is an SSL implementation written
   6  * by Eric Young (eay@cryptsoft.com).
   7  * The implementation was written so as to conform with Netscapes SSL.
   8  *
   9  * This library is free for commercial and non-commercial use as long as
  10  * the following conditions are aheared to.  The following conditions
  11  * apply to all code found in this distribution, be it the RC4, RSA,
  12  * lhash, DES, etc., code; not just the SSL code.  The SSL documentation
  13  * included with this distribution is covered by the same copyright terms
  14  * except that the holder is Tim Hudson (tjh@cryptsoft.com).
  15  *
  16  * Copyright remains Eric Young's, and as such any Copyright notices in
  17  * the code are not to be removed.
  18  * If this package is used in a product, Eric Young should be given attribution
  19  * as the author of the parts of the library used.
  20  * This can be in the form of a textual message at program startup or
  21  * in documentation (online or textual) provided with the package.
  22  *
  23  * Redistribution and use in source and binary forms, with or without
  24  * modification, are permitted provided that the following conditions
  25  * are met:
  26  * 1. Redistributions of source code must retain the copyright
  27  *    notice, this list of conditions and the following disclaimer.
  28  * 2. Redistributions in binary form must reproduce the above copyright
  29  *    notice, this list of conditions and the following disclaimer in the
  30  *    documentation and/or other materials provided with the distribution.
  31  * 3. All advertising materials mentioning features or use of this software
  32  *    must display the following acknowledgement:
  33  *    "This product includes cryptographic software written by
  34  *     Eric Young (eay@cryptsoft.com)"
  35  *    The word 'cryptographic' can be left out if the rouines from the library
  36  *    being used are not cryptographic related :-).
  37  * 4. If you include any Windows specific code (or a derivative thereof) from
  38  *    the apps directory (application code) you must include an acknowledgement:
  39  *    "This product includes software written by Tim Hudson (tjh@cryptsoft.com)"
  40  *
  41  * THIS SOFTWARE IS PROVIDED BY ERIC YOUNG ``AS IS'' AND
  42  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  43  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  44  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
  45  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  46  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  47  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  48  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  49  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  50  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  51  * SUCH DAMAGE.
  52  *
  53  * The licence and distribution terms for any publically available version or
  54  * derivative of this code cannot be changed.  i.e. this code cannot simply be
  55  * copied and put under another distribution licence
  56  * [including the GNU Public Licence.]
  57  */
  58
  59 #include <stdio.h>
  60 #include "internal/cryptlib.h"
  61 #include <openssl/rand.h>
  62 #include <openssl/dh.h>
  63 #include "internal/bn_int.h"
  64
  65 static int generate_key(DH *dh);
  66 static int compute_key(unsigned char *key, const BIGNUM *pub_key, DH *dh);
  67 static int dh_bn_mod_exp(const DH *dh, BIGNUM *r,
  68                          const BIGNUM *a, const BIGNUM *p,
  69                          const BIGNUM *m, BN_CTX *ctx, BN_MONT_CTX *m_ctx);
  70 static int dh_init(DH *dh);
  71 static int dh_finish(DH *dh);
  72
  73 int DH_generate_key(DH *dh)
  74 {
  75     return dh->meth->generate_key(dh);
  76 }
  77
  78 int DH_compute_key(unsigned char *key, const BIGNUM *pub_key, DH *dh)
  79 {
  80     return dh->meth->compute_key(key, pub_key, dh);
  81 }
  82
  83 int DH_compute_key_padded(unsigned char *key, const BIGNUM *pub_key, DH *dh)
  84 {
  85     int rv, pad;
  86     rv = dh->meth->compute_key(key, pub_key, dh);
  87     if (rv <= 0)
  88         return rv;
  89     pad = BN_num_bytes(dh->p) - rv;
  90     if (pad > 0) {
  91         memmove(key + pad, key, rv);
  92         memset(key, 0, pad);
  93     }
  94     return rv + pad;
  95 }
  96
  97 static DH_METHOD dh_ossl = {
  98     "OpenSSL DH Method",
  99     generate_key,
 100     compute_key,
 101     dh_bn_mod_exp,
 102     dh_init,
 103     dh_finish,
 104     DH_FLAG_FIPS_METHOD,
 105     NULL,
 106     NULL
 107 };
 108
 109 const DH_METHOD *DH_OpenSSL(void)
 110 {
 111     return &dh_ossl;
 112 }
 113
 114 static int generate_key(DH *dh)
 115 {
 116     int ok = 0;
 117     int generate_new_key = 0;
 118     unsigned l;
 119     BN_CTX *ctx;
 120     BN_MONT_CTX *mont = NULL;
 121     BIGNUM *pub_key = NULL, *priv_key = NULL;
 122
 123     ctx = BN_CTX_new();
 124     if (ctx == NULL)
 125         goto err;
 126
 127     if (dh->priv_key == NULL) {
 128         priv_key = BN_secure_new();
 129         if (priv_key == NULL)
 130             goto err;
 131         generate_new_key = 1;
 132     } else
 133         priv_key = dh->priv_key;
 134
 135     if (dh->pub_key == NULL) {
 136         pub_key = BN_new();
 137         if (pub_key == NULL)
 138             goto err;
 139     } else
 140         pub_key = dh->pub_key;
 141
 142     if (dh->flags & DH_FLAG_CACHE_MONT_P) {
 143         mont = BN_MONT_CTX_set_locked(&dh->method_mont_p,
 144                                       CRYPTO_LOCK_DH, dh->p, ctx);
 145         if (!mont)
 146             goto err;
 147     }
 148
 149     if (generate_new_key) {
 150         if (dh->q) {
 151             do {
 152                 if (!BN_rand_range(priv_key, dh->q))
 153                     goto err;
 154             }
 155             while (BN_is_zero(priv_key) || BN_is_one(priv_key));
 156         } else {
 157             /* secret exponent length */
 158             l = dh->length ? dh->length : BN_num_bits(dh->p) - 1;
 159             if (!BN_rand(priv_key, l, 0, 0))
 160                 goto err;
 161         }
 162     }
 163
 164     {
 165         BIGNUM *local_prk = NULL;
 166         BIGNUM *prk;
 167
 168         if ((dh->flags & DH_FLAG_NO_EXP_CONSTTIME) == 0) {
 169             local_prk = prk = BN_new();
 170             if (local_prk == NULL)
 171                 goto err;
 172             BN_with_flags(prk, priv_key, BN_FLG_CONSTTIME);
 173         } else {
 174             prk = priv_key;
 175         }
 176
 177         if (!dh->meth->bn_mod_exp(dh, pub_key, dh->g, prk, dh->p, ctx, mont)) {
 178             BN_free(local_prk);
 179             goto err;
 180         }
 181         /* We MUST free local_prk before any further use of priv_key */
 182         BN_free(local_prk);
 183     }
 184
 185     dh->pub_key = pub_key;
 186     dh->priv_key = priv_key;
 187     ok = 1;
 188  err:
 189     if (ok != 1)
 190         DHerr(DH_F_GENERATE_KEY, ERR_R_BN_LIB);
 191
 192     if (pub_key != dh->pub_key)
 193         BN_free(pub_key);
 194     if (priv_key != dh->priv_key)
 195         BN_free(priv_key);
 196     BN_CTX_free(ctx);
 197     return (ok);
 198 }
 199
 200 static int compute_key(unsigned char *key, const BIGNUM *pub_key, DH *dh)
 201 {
 202     BN_CTX *ctx = NULL;
 203     BN_MONT_CTX *mont = NULL;
 204     BIGNUM *tmp;
 205     int ret = -1;
 206     int check_result;
 207
 208     if (BN_num_bits(dh->p) > OPENSSL_DH_MAX_MODULUS_BITS) {
 209         DHerr(DH_F_COMPUTE_KEY, DH_R_MODULUS_TOO_LARGE);
 210         goto err;
 211     }
 212
 213     ctx = BN_CTX_new();
 214     if (ctx == NULL)
 215         goto err;
 216     BN_CTX_start(ctx);
 217     tmp = BN_CTX_get(ctx);
 218
 219     if (dh->priv_key == NULL) {
 220         DHerr(DH_F_COMPUTE_KEY, DH_R_NO_PRIVATE_VALUE);
 221         goto err;
 222     }
 223
 224     if (dh->flags & DH_FLAG_CACHE_MONT_P) {
 225         mont = BN_MONT_CTX_set_locked(&dh->method_mont_p,
 226                                       CRYPTO_LOCK_DH, dh->p, ctx);
 227         if ((dh->flags & DH_FLAG_NO_EXP_CONSTTIME) == 0) {
 228             /* XXX */
 229             BN_set_flags(dh->priv_key, BN_FLG_CONSTTIME);
 230         }
 231         if (!mont)
 232             goto err;
 233     }
 234
 235     if (!DH_check_pub_key(dh, pub_key, &check_result) || check_result) {
 236         DHerr(DH_F_COMPUTE_KEY, DH_R_INVALID_PUBKEY);
 237         goto err;
 238     }
 239
 240     if (!dh->
 241         meth->bn_mod_exp(dh, tmp, pub_key, dh->priv_key, dh->p, ctx, mont)) {
 242         DHerr(DH_F_COMPUTE_KEY, ERR_R_BN_LIB);
 243         goto err;
 244     }
 245
 246     ret = BN_bn2bin(tmp, key);
 247  err:
 248     if (ctx != NULL) {
 249         BN_CTX_end(ctx);
 250         BN_CTX_free(ctx);
 251     }
 252     return (ret);
 253 }
 254
 255 static int dh_bn_mod_exp(const DH *dh, BIGNUM *r,
 256                          const BIGNUM *a, const BIGNUM *p,
 257                          const BIGNUM *m, BN_CTX *ctx, BN_MONT_CTX *m_ctx)
 258 {
 259     /*
 260      * If a is only one word long and constant time is false, use the faster
 261      * exponenentiation function.
 262      */
 263     if (bn_get_top(a) == 1 && ((dh->flags & DH_FLAG_NO_EXP_CONSTTIME) != 0)) {
 264         BN_ULONG A = bn_get_words(a)[0];
 265         return BN_mod_exp_mont_word(r, A, p, m, ctx, m_ctx);
 266     } else
 267         return BN_mod_exp_mont(r, a, p, m, ctx, m_ctx);
 268 }
 269
 270 static int dh_init(DH *dh)
 271 {
 272     dh->flags |= DH_FLAG_CACHE_MONT_P;
 273     return (1);
 274 }
 275
 276 static int dh_finish(DH *dh)
 277 {
 278     BN_MONT_CTX_free(dh->method_mont_p);
 279     return (1);
 280 }