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

   1 /* dsa-sign.c
   2  *
   3  * The DSA publickey algorithm.
   4  */
   5
   6 /* nettle, low-level cryptographics library
   7  *
   8  * Copyright (C) 2002, 2010 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 <assert.h>
  31 #include <stdlib.h>
  32
  33 #include "dsa.h"
  34
  35 #include "bignum.h"
  36
  37
  38 int
  39 _dsa_sign(const struct dsa_public_key *pub,
  40           const struct dsa_private_key *key,
  41           void *random_ctx, nettle_random_func *random,
  42           unsigned digest_size,
  43           const uint8_t *digest,
  44           struct dsa_signature *signature)
  45 {
  46   mpz_t k;
  47   mpz_t h;
  48   mpz_t tmp;
  49
  50   /* Require precise match of bitsize of q and hash size. The general
  51      description of DSA in FIPS186-3 allows both larger and smaller q;
  52      in the the latter case, the hash must be truncated to the right
  53      number of bits. */
  54   if (mpz_sizeinbase(pub->q, 2) != 8 * digest_size)
  55     return 0;
  56
  57   /* Select k, 0<k<q, randomly */
  58   mpz_init_set(tmp, pub->q);
  59   mpz_sub_ui(tmp, tmp, 1);
  60
  61   mpz_init(k);
  62   nettle_mpz_random(k, random_ctx, random, tmp);
  63   mpz_add_ui(k, k, 1);
  64
  65   /* Compute r = (g^k (mod p)) (mod q) */
  66   mpz_powm(tmp, pub->g, k, pub->p);
  67   mpz_fdiv_r(signature->r, tmp, pub->q);
  68
  69   /* Compute hash */
  70   mpz_init(h);
  71   nettle_mpz_set_str_256_u(h, digest_size, digest);
  72
  73   /* Compute k^-1 (mod q) */
  74   if (!mpz_invert(k, k, pub->q))
  75     /* What do we do now? The key is invalid. */
  76     return 0;
  77
  78   /* Compute signature s = k^-1 (h + xr) (mod q) */
  79   mpz_mul(tmp, signature->r, key->x);
  80   mpz_fdiv_r(tmp, tmp, pub->q);
  81   mpz_add(tmp, tmp, h);
  82   mpz_mul(tmp, tmp, k);
  83   mpz_fdiv_r(signature->s, tmp, pub->q);
  84
  85   mpz_clear(k);
  86   mpz_clear(h);
  87   mpz_clear(tmp);
  88
  89   return 1;
  90 }