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41 results

array.c

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  • rsa_md5.c 2.98 KiB
    /* rsa_md5.c
     *
     * Signatures using RSA and MD5.
     */
    
    /* nettle, low-level cryptographics library
     *
     * Copyright (C) 2001 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
    
    #if HAVE_LIBGMP
    
    #include "rsa.h"
    
    #include "bignum.h"
    
    #include <assert.h>
    #include <stdlib.h>
    #include <string.h>
    
    /* Forward declarations */
    static void
    pkcs1_encode_md5(mpz_t m, unsigned length, struct md5_ctx *hash);
    
    void
    rsa_md5_sign(struct rsa_private_key *key,
                 struct md5_ctx *hash,
                 mpz_t s)
    {
      assert(key->size >= 45);
    
      pkcs1_encode_md5(s, key->size - 1, hash);
    
      rsa_compute_root(key, s, s);
    }
    
    int
    rsa_md5_verify(struct rsa_public_key *key,
                   struct md5_ctx *hash,
                   const mpz_t s)
    {
      int res;
      
      mpz_t m1;
      mpz_t m2;
      
      if ( (mpz_sgn(s) <= 0)
           || (mpz_cmp(s, key->n) >= 0) )
        return 0;
           
      mpz_init(m1); mpz_init(m2);
      
      mpz_powm(m1, s, key->e, key->n);
    
      /* FIXME: Is it cheaper to convert m1 to a string and check that? */
      pkcs1_encode_md5(m2, key->size - 1, hash);
      res = !mpz_cmp(m1, m2);
    
      mpz_clear(m1); mpz_clear(m2);
    
      return res;
    }
    
    /* From pkcs-1v2
     *
     *   md5 OBJECT IDENTIFIER ::=
     *     {iso(1) member-body(2) US(840) rsadsi(113549) digestAlgorithm(2) 5}
     *
     * The parameters part of the algorithm identifier is NULL:
     *
     *   md5Identifier ::= AlgorithmIdentifier {md5, NULL}
     */
    
    static const uint8_t
    md5_prefix[] =
    {
      /* 18 octets prefix, 16 octets hash, 34 total. */
      0x30,       32, /* SEQUENCE */
        0x30,     12, /* SEQUENCE */
          0x06,    8, /* OBJECT IDENTIFIER */
      	0x2a, 0x86, 0x48, 0x86, 0xf7, 0x0d, 0x02, 0x05,
          0x05,    0, /* NULL */
        0x04,     16  /* OCTET STRING */
          /* Here comes the raw hash value */
    };
    
    static void
    pkcs1_encode_md5(mpz_t m, unsigned length, struct md5_ctx *hash)
    {
      uint8_t *em = alloca(length);
      unsigned i;
    
      assert(length >= MD5_DIGEST_SIZE);
    
      i = length - MD5_DIGEST_SIZE;
      
      md5_digest(hash, MD5_DIGEST_SIZE, em + i);
    
      assert(i >= sizeof(md5_prefix));
    
      i -= sizeof(md5_prefix);
      memcpy(em + i, md5_prefix, sizeof(md5_prefix));
    
      assert(i);
      em[--i] = 0;
    
      assert(i >= 9);
    
      em[0] = 1;
      memset(em + 1, 0xff, i - 1);
    
      nettle_mpz_set_str_256(m, length, em);
    }
    
    #endif /* HAVE_LIBGMP */