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dh_key.c

/* crypto/dh/dh_key.c */
/* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
 * All rights reserved.
 *
 * This package is an SSL implementation written
 * by Eric Young (eay@cryptsoft.com).
 * The implementation was written so as to conform with Netscapes SSL.
 * 
 * This library is free for commercial and non-commercial use as long as
 * the following conditions are aheared to.  The following conditions
 * apply to all code found in this distribution, be it the RC4, RSA,
 * lhash, DES, etc., code; not just the SSL code.  The SSL documentation
 * included with this distribution is covered by the same copyright terms
 * except that the holder is Tim Hudson (tjh@cryptsoft.com).
 * 
 * Copyright remains Eric Young's, and as such any Copyright notices in
 * the code are not to be removed.
 * If this package is used in a product, Eric Young should be given attribution
 * as the author of the parts of the library used.
 * This can be in the form of a textual message at program startup or
 * in documentation (online or textual) provided with the package.
 * 
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *    "This product includes cryptographic software written by
 *     Eric Young (eay@cryptsoft.com)"
 *    The word 'cryptographic' can be left out if the rouines from the library
 *    being used are not cryptographic related :-).
 * 4. If you include any Windows specific code (or a derivative thereof) from 
 *    the apps directory (application code) you must include an acknowledgement:
 *    "This product includes software written by Tim Hudson (tjh@cryptsoft.com)"
 * 
 * THIS SOFTWARE IS PROVIDED BY ERIC YOUNG ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 * 
 * The licence and distribution terms for any publically available version or
 * derivative of this code cannot be changed.  i.e. this code cannot simply be
 * copied and put under another distribution licence
 * [including the GNU Public Licence.]
 */

#include <stdio.h>
#include "cryptlib.h"
#include <openssl/bn.h>
#include <openssl/rand.h>
#include <openssl/dh.h>

static int generate_key(DH *dh);
static int compute_key(unsigned char *key, const BIGNUM *pub_key, DH *dh);
static int dh_bn_mod_exp(const DH *dh, BIGNUM *r,
                  const BIGNUM *a, const BIGNUM *p,
                  const BIGNUM *m, BN_CTX *ctx,
                  BN_MONT_CTX *m_ctx);
static int dh_init(DH *dh);
static int dh_finish(DH *dh);

int DH_generate_key(DH *dh)
      {
      return dh->meth->generate_key(dh);
      }

int DH_compute_key(unsigned char *key, const BIGNUM *pub_key, DH *dh)
      {
      return dh->meth->compute_key(key, pub_key, dh);
      }

static DH_METHOD dh_ossl = {
"OpenSSL DH Method",
generate_key,
compute_key,
dh_bn_mod_exp,
dh_init,
dh_finish,
0,
NULL,
NULL
};

const DH_METHOD *DH_OpenSSL(void)
{
      return &dh_ossl;
}

static int generate_key(DH *dh)
      {
      int ok=0;
      int generate_new_key=0;
      unsigned l;
      BN_CTX *ctx;
      BN_MONT_CTX *mont=NULL;
      BIGNUM *pub_key=NULL,*priv_key=NULL;

      ctx = BN_CTX_new();
      if (ctx == NULL) goto err;

      if (dh->priv_key == NULL)
            {
            priv_key=BN_new();
            if (priv_key == NULL) goto err;
            generate_new_key=1;
            }
      else
            priv_key=dh->priv_key;

      if (dh->pub_key == NULL)
            {
            pub_key=BN_new();
            if (pub_key == NULL) goto err;
            }
      else
            pub_key=dh->pub_key;


      if (dh->flags & DH_FLAG_CACHE_MONT_P)
            {
            mont = BN_MONT_CTX_set_locked(&dh->method_mont_p,
                        CRYPTO_LOCK_DH, dh->p, ctx);
            if (!mont)
                  goto err;
            }

      if (generate_new_key)
            {
            l = dh->length ? dh->length : BN_num_bits(dh->p)-1; /* secret exponent length */
            if (!BN_rand(priv_key, l, 0, 0)) goto err;
            }

      {
            BIGNUM local_prk;
            BIGNUM *prk;

            if ((dh->flags & DH_FLAG_NO_EXP_CONSTTIME) == 0)
                  {
                  BN_init(&local_prk);
                  prk = &local_prk;
                  BN_with_flags(prk, priv_key, BN_FLG_CONSTTIME);
                  }
            else
                  prk = priv_key;

            if (!dh->meth->bn_mod_exp(dh, pub_key, dh->g, prk, dh->p, ctx, mont)) goto err;
      }
            
      dh->pub_key=pub_key;
      dh->priv_key=priv_key;
      ok=1;
err:
      if (ok != 1)
            DHerr(DH_F_GENERATE_KEY,ERR_R_BN_LIB);

      if ((pub_key != NULL)  && (dh->pub_key == NULL))  BN_free(pub_key);
      if ((priv_key != NULL) && (dh->priv_key == NULL)) BN_free(priv_key);
      BN_CTX_free(ctx);
      return(ok);
      }

static int compute_key(unsigned char *key, const BIGNUM *pub_key, DH *dh)
      {
      BN_CTX *ctx=NULL;
      BN_MONT_CTX *mont=NULL;
      BIGNUM *tmp;
      int ret= -1;
        int check_result;

      if (BN_num_bits(dh->p) > OPENSSL_DH_MAX_MODULUS_BITS)
            {
            DHerr(DH_F_COMPUTE_KEY,DH_R_MODULUS_TOO_LARGE);
            goto err;
            }

      ctx = BN_CTX_new();
      if (ctx == NULL) goto err;
      BN_CTX_start(ctx);
      tmp = BN_CTX_get(ctx);
      
      if (dh->priv_key == NULL)
            {
            DHerr(DH_F_COMPUTE_KEY,DH_R_NO_PRIVATE_VALUE);
            goto err;
            }

      if (dh->flags & DH_FLAG_CACHE_MONT_P)
            {
            mont = BN_MONT_CTX_set_locked(&dh->method_mont_p,
                        CRYPTO_LOCK_DH, dh->p, ctx);
            if ((dh->flags & DH_FLAG_NO_EXP_CONSTTIME) == 0)
                  {
                  /* XXX */
                  BN_set_flags(dh->priv_key, BN_FLG_CONSTTIME);
                  }
            if (!mont)
                  goto err;
            }

        if (!DH_check_pub_key(dh, pub_key, &check_result) || check_result)
            {
            DHerr(DH_F_COMPUTE_KEY,DH_R_INVALID_PUBKEY);
            goto err;
            }

      if (!dh->meth->bn_mod_exp(dh, tmp, pub_key, dh->priv_key,dh->p,ctx,mont))
            {
            DHerr(DH_F_COMPUTE_KEY,ERR_R_BN_LIB);
            goto err;
            }

      ret=BN_bn2bin(tmp,key);
err:
      if (ctx != NULL)
            {
            BN_CTX_end(ctx);
            BN_CTX_free(ctx);
            }
      return(ret);
      }

static int dh_bn_mod_exp(const DH *dh, BIGNUM *r,
                  const BIGNUM *a, const BIGNUM *p,
                  const BIGNUM *m, BN_CTX *ctx,
                  BN_MONT_CTX *m_ctx)
      {
      /* If a is only one word long and constant time is false, use the faster
       * exponenentiation function.
       */
      if (a->top == 1 && ((dh->flags & DH_FLAG_NO_EXP_CONSTTIME) != 0))
            {
            BN_ULONG A = a->d[0];
            return BN_mod_exp_mont_word(r,A,p,m,ctx,m_ctx);
            }
      else
            return BN_mod_exp_mont(r,a,p,m,ctx,m_ctx);
      }


static int dh_init(DH *dh)
      {
      dh->flags |= DH_FLAG_CACHE_MONT_P;
      return(1);
      }

static int dh_finish(DH *dh)
      {
      if(dh->method_mont_p)
            BN_MONT_CTX_free(dh->method_mont_p);
      return(1);
      }

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