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buffer-init.c

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  • Forked from Nettle / nettle
    Source project has a limited visibility.
    dsa-sign.c 2.36 KiB
    /* dsa-sign.c
     *
     * The DSA publickey algorithm.
     */
    
    /* nettle, low-level cryptographics library
     *
     * Copyright (C) 2002, 2010 Niels Mller
     *  
     * The nettle library is free software; you can redistribute it and/or modify
     * it under the terms of the GNU Lesser General Public License as published by
     * the Free Software Foundation; either version 2.1 of the License, or (at your
     * option) any later version.
     * 
     * The nettle library is distributed in the hope that it will be useful, but
     * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
     * or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
     * License for more details.
     * 
     * You should have received a copy of the GNU Lesser General Public License
     * along with the nettle library; see the file COPYING.LIB.  If not, write to
     * the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
     * MA 02111-1307, USA.
     */
    
    #if HAVE_CONFIG_H
    # include "config.h"
    #endif
    
    #include <assert.h>
    #include <stdlib.h>
    
    #include "dsa.h"
    
    #include "bignum.h"
    
    
    int
    _dsa_sign(const struct dsa_public_key *pub,
    	  const struct dsa_private_key *key,
    	  void *random_ctx, nettle_random_func random,
    	  unsigned digest_size,
    	  const uint8_t *digest,
    	  struct dsa_signature *signature)
    {
      mpz_t k;
      mpz_t h;
      mpz_t tmp;
    
      /* Require precise match of bitsize of q and hash size. The general
         description of DSA in FIPS186-3 allows both larger and smaller q;
         in the the latter case, the hash must be truncated to the right
         number of bits. */
      if (mpz_sizeinbase(pub->q, 2) != 8 * digest_size)
        return 0;
    
      /* Select k, 0<k<q, randomly */
      mpz_init_set(tmp, pub->q);
      mpz_sub_ui(tmp, tmp, 1);
    
      mpz_init(k);
      nettle_mpz_random(k, random_ctx, random, tmp);
      mpz_add_ui(k, k, 1);
    
      /* Compute r = (g^k (mod p)) (mod q) */
      mpz_powm(tmp, pub->g, k, pub->p);
      mpz_fdiv_r(signature->r, tmp, pub->q);
    
      /* Compute hash */
      mpz_init(h);
      nettle_mpz_set_str_256_u(h, digest_size, digest);
    
      /* Compute k^-1 (mod q) */
      if (!mpz_invert(k, k, pub->q))
        /* What do we do now? The key is invalid. */
        return 0;
    
      /* Compute signature s = k^-1 (h + xr) (mod q) */
      mpz_mul(tmp, signature->r, key->x);
      mpz_fdiv_r(tmp, tmp, pub->q);
      mpz_add(tmp, tmp, h);
      mpz_mul(tmp, tmp, k);
      mpz_fdiv_r(signature->s, tmp, pub->q);
    
      mpz_clear(k);
      mpz_clear(h);
      mpz_clear(tmp);
    
      return 1;
    }