release/src/router/nettle/dsa-verify.c

   1 /* dsa-verify.c
   2  *
   3  * The DSA publickey algorithm.
   4  */
   5
   6 /* nettle, low-level cryptographics library
   7  *
   8  * Copyright (C) 2002, 2003 Niels Möller
   9  *
  10  * The nettle library is free software; you can redistribute it and/or modify
  11  * it under the terms of the GNU Lesser General Public License as published by
  12  * the Free Software Foundation; either version 2.1 of the License, or (at your
  13  * option) any later version.
  14  *
  15  * The nettle library is distributed in the hope that it will be useful, but
  16  * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
  17  * or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
  18  * License for more details.
  19  *
  20  * You should have received a copy of the GNU Lesser General Public License
  21  * along with the nettle library; see the file COPYING.LIB.  If not, write to
  22  * the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
  23  * MA 02111-1301, USA.
  24  */
  25
  26 #if HAVE_CONFIG_H
  27 # include "config.h"
  28 #endif
  29
  30 #include <stdlib.h>
  31
  32 #include "dsa.h"
  33
  34 #include "bignum.h"
  35
  36 int
  37 _dsa_verify(const struct dsa_public_key *key,
  38             unsigned digest_size,
  39             const uint8_t *digest,
  40             const struct dsa_signature *signature)
  41 {
  42   mpz_t w;
  43   mpz_t tmp;
  44   mpz_t v;
  45
  46   int res;
  47
  48   if (mpz_sizeinbase(key->q, 2) != 8 * digest_size)
  49     return 0;
  50
  51   /* Check that r and s are in the proper range */
  52   if (mpz_sgn(signature->r) <= 0 || mpz_cmp(signature->r, key->q) >= 0)
  53     return 0;
  54
  55   if (mpz_sgn(signature->s) <= 0 || mpz_cmp(signature->s, key->q) >= 0)
  56     return 0;
  57
  58   mpz_init(w);
  59
  60   /* Compute w = s^-1 (mod q) */
  61
  62   /* NOTE: In gmp-2, mpz_invert sometimes generates negative inverses,
  63    * so we need gmp-3 or better. */
  64   if (!mpz_invert(w, signature->s, key->q))
  65     {
  66       mpz_clear(w);
  67       return 0;
  68     }
  69
  70   mpz_init(tmp);
  71   mpz_init(v);
  72
  73   /* The message digest */
  74   nettle_mpz_set_str_256_u(tmp, digest_size, digest);
  75
  76   /* v = g^{w * h (mod q)} (mod p)  */
  77   mpz_mul(tmp, tmp, w);
  78   mpz_fdiv_r(tmp, tmp, key->q);
  79
  80   mpz_powm(v, key->g, tmp, key->p);
  81
  82   /* y^{w * r (mod q) } (mod p) */
  83   mpz_mul(tmp, signature->r, w);
  84   mpz_fdiv_r(tmp, tmp, key->q);
  85
  86   mpz_powm(tmp, key->y, tmp, key->p);
  87
  88   /* v = (g^{w * h} * y^{w * r} (mod p) ) (mod q) */
  89   mpz_mul(v, v, tmp);
  90   mpz_fdiv_r(v, v, key->p);
  91
  92   mpz_fdiv_r(v, v, key->q);
  93
  94   res = !mpz_cmp(v, signature->r);
  95
  96   mpz_clear(w);
  97   mpz_clear(tmp);
  98   mpz_clear(v);
  99
 100   return res;
 101 }