src/crypto/dh/check.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 <openssl/dh.h>

#include <openssl/bn.h>


int DH_check_pub_key(const DH *dh, const BIGNUM *pub_key, int *out_flags) {
  *out_flags = 0;

  BN_CTX *ctx = BN_CTX_new();
  if (ctx == NULL) {
    return 0;
  }
  BN_CTX_start(ctx);

  int ok = 0;

  // Check |pub_key| is greater than 1.
  BIGNUM *tmp = BN_CTX_get(ctx);
  if (tmp == NULL ||
      !BN_set_word(tmp, 1)) {
    goto err;
  }
  if (BN_cmp(pub_key, tmp) <= 0) {
    *out_flags |= DH_CHECK_PUBKEY_TOO_SMALL;
  }

  // Check |pub_key| is less than |dh->p| - 1.
  if (!BN_copy(tmp, dh->p) ||
      !BN_sub_word(tmp, 1)) {
    goto err;
  }
  if (BN_cmp(pub_key, tmp) >= 0) {
    *out_flags |= DH_CHECK_PUBKEY_TOO_LARGE;
  }

  if (dh->q != NULL) {
    // Check |pub_key|^|dh->q| is 1 mod |dh->p|. This is necessary for RFC 5114
    // groups which are not safe primes but pick a generator on a prime-order
    // subgroup of size |dh->q|.
    if (!BN_mod_exp_mont(tmp, pub_key, dh->q, dh->p, ctx, NULL)) {
      goto err;
    }
    if (!BN_is_one(tmp)) {
      *out_flags |= DH_CHECK_PUBKEY_INVALID;
    }
  }

  ok = 1;

err:
  BN_CTX_end(ctx);
  BN_CTX_free(ctx);
  return ok;
}


int DH_check(const DH *dh, int *out_flags) {
  // Check that p is a safe prime and if g is 2, 3 or 5, check that it is a
  // suitable generator where:
  //   for 2, p mod 24 == 11
  //   for 3, p mod 12 == 5
  //   for 5, p mod 10 == 3 or 7
  // should hold.
  int ok = 0, r;
  BN_CTX *ctx = NULL;
  BN_ULONG l;
  BIGNUM *t1 = NULL, *t2 = NULL;

  *out_flags = 0;
  ctx = BN_CTX_new();
  if (ctx == NULL) {
    goto err;
  }
  BN_CTX_start(ctx);
  t1 = BN_CTX_get(ctx);
  if (t1 == NULL) {
    goto err;
  }
  t2 = BN_CTX_get(ctx);
  if (t2 == NULL) {
    goto err;
  }

  if (dh->q) {
    if (BN_cmp(dh->g, BN_value_one()) <= 0) {
      *out_flags |= DH_CHECK_NOT_SUITABLE_GENERATOR;
    } else if (BN_cmp(dh->g, dh->p) >= 0) {
      *out_flags |= DH_CHECK_NOT_SUITABLE_GENERATOR;
    } else {
      // Check g^q == 1 mod p
      if (!BN_mod_exp_mont(t1, dh->g, dh->q, dh->p, ctx, NULL)) {
        goto err;
      }
      if (!BN_is_one(t1)) {
        *out_flags |= DH_CHECK_NOT_SUITABLE_GENERATOR;
      }
    }
    r = BN_is_prime_ex(dh->q, BN_prime_checks, ctx, NULL);
    if (r < 0) {
      goto err;
    }
    if (!r) {
      *out_flags |= DH_CHECK_Q_NOT_PRIME;
    }
    // Check p == 1 mod q  i.e. q divides p - 1
    if (!BN_div(t1, t2, dh->p, dh->q, ctx)) {
      goto err;
    }
    if (!BN_is_one(t2)) {
      *out_flags |= DH_CHECK_INVALID_Q_VALUE;
    }
    if (dh->j && BN_cmp(dh->j, t1)) {
      *out_flags |= DH_CHECK_INVALID_J_VALUE;
    }
  } else if (BN_is_word(dh->g, DH_GENERATOR_2)) {
    l = BN_mod_word(dh->p, 24);
    if (l == (BN_ULONG)-1) {
      goto err;
    }
    if (l != 11) {
      *out_flags |= DH_CHECK_NOT_SUITABLE_GENERATOR;
    }
  } else if (BN_is_word(dh->g, DH_GENERATOR_5)) {
    l = BN_mod_word(dh->p, 10);
    if (l == (BN_ULONG)-1) {
      goto err;
    }
    if (l != 3 && l != 7) {
      *out_flags |= DH_CHECK_NOT_SUITABLE_GENERATOR;
    }
  } else {
    *out_flags |= DH_CHECK_UNABLE_TO_CHECK_GENERATOR;
  }

  r = BN_is_prime_ex(dh->p, BN_prime_checks, ctx, NULL);
  if (r < 0) {
    goto err;
  }
  if (!r) {
    *out_flags |= DH_CHECK_P_NOT_PRIME;
  } else if (!dh->q) {
    if (!BN_rshift1(t1, dh->p)) {
      goto err;
    }
    r = BN_is_prime_ex(t1, BN_prime_checks, ctx, NULL);
    if (r < 0) {
      goto err;
    }
    if (!r) {
      *out_flags |= DH_CHECK_P_NOT_SAFE_PRIME;
    }
  }
  ok = 1;

err:
  if (ctx != NULL) {
    BN_CTX_end(ctx);
    BN_CTX_free(ctx);
  }
  return ok;
}