/*

 * Crypto wrapper for internal crypto implementation - modexp

 * Copyright (c) 2006-2009, Jouni Malinen <j@w1.fi>

 *

 * This software may be distributed under the terms of the BSD license.

 * See README for more details.

 */

#include "includes.h"

#include "common.h"

#include "tls/bignum.h"

#include "crypto.h"

int crypto_dh_init(u8 generator, const u8 *prime, size_t prime_len, u8 *privkey,

       u8 *pubkey)

{

  size_t pubkey_len, pad;

  if (os_get_random(privkey, prime_len) < 0)

    return -1;

  if (os_memcmp(privkey, prime, prime_len) > 0) {

    /* Make sure private value is smaller than prime */

    privkey[0] = 0;

  }

  pubkey_len = prime_len;

  if (crypto_mod_exp(&generator, 1, privkey, prime_len, prime, prime_len,

         pubkey, &pubkey_len) < 0)

    return -1;

  if (pubkey_len < prime_len) {

    pad = prime_len - pubkey_len;

    os_memmove(pubkey + pad, pubkey, pubkey_len);

    os_memset(pubkey, 0, pad);

  }

  return 0;

}

int crypto_dh_derive_secret(u8 generator, const u8 *prime, size_t prime_len,

          const u8 *order, size_t order_len,

          const u8 *privkey, size_t privkey_len,

          const u8 *pubkey, size_t pubkey_len,

          u8 *secret, size_t *len)

{

  struct bignum *pub;

  int res = -1;

  if (pubkey_len > prime_len ||

      (pubkey_len == prime_len &&

       os_memcmp(pubkey, prime, prime_len) >= 0))

    return -1;

  pub = bignum_init();

  if (!pub || bignum_set_unsigned_bin(pub, pubkey, pubkey_len) < 0 ||

      bignum_cmp_d(pub, 1) <= 0)

    goto fail;

  if (order) {

    struct bignum *p, *q, *tmp;

    int failed;

    /* verify: pubkey^q == 1 mod p */

    p = bignum_init();

    q = bignum_init();

    tmp = bignum_init();

    failed = !p || !q || !tmp ||

      bignum_set_unsigned_bin(p, prime, prime_len) < 0 ||

      bignum_set_unsigned_bin(q, order, order_len) < 0 ||

      bignum_exptmod(pub, q, p, tmp) < 0 ||

      bignum_cmp_d(tmp, 1) != 0;

    bignum_deinit(p);

    bignum_deinit(q);

    bignum_deinit(tmp);

    if (failed)

      goto fail;

  }

  res = crypto_mod_exp(pubkey, pubkey_len, privkey, privkey_len,

           prime, prime_len, secret, len);

fail:

  bignum_deinit(pub);

  return res;

}

int crypto_mod_exp(const u8 *base, size_t base_len,

       const u8 *power, size_t power_len,

       const u8 *modulus, size_t modulus_len,

       u8 *result, size_t *result_len)

{

  struct bignum *bn_base, *bn_exp, *bn_modulus, *bn_result;

  int ret = -1;

  bn_base = bignum_init();

  bn_exp = bignum_init();

  bn_modulus = bignum_init();

  bn_result = bignum_init();

  if (bn_base == NULL || bn_exp == NULL || bn_modulus == NULL ||

      bn_result == NULL)

    goto error;

  if (bignum_set_unsigned_bin(bn_base, base, base_len) < 0 ||

      bignum_set_unsigned_bin(bn_exp, power, power_len) < 0 ||

      bignum_set_unsigned_bin(bn_modulus, modulus, modulus_len) < 0)

    goto error;

  if (bignum_exptmod(bn_base, bn_exp, bn_modulus, bn_result) < 0)

    goto error;

  ret = bignum_get_unsigned_bin(bn_result, result, result_len);

error:

  bignum_deinit(bn_base);

  bignum_deinit(bn_exp);

  bignum_deinit(bn_modulus);

  bignum_deinit(bn_result);

  return ret;

}