rsa.c

/* rsa.c
 *
 * The RSA publickey algorithm.
 */

/* 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"

/* FIXME: Perhaps we should split this into several functions, so that
 * one can link in the signature functions without also getting the
 * verify functions. */

int
rsa_prepare_public_key(struct rsa_public_key *key)
{
  unsigned size = (mpz_sizeinbase(key->n, 2) + 7) / 8;

  /* For PKCS#1 to make sense, the size of the modulo, in octets, must
   * be at least 11 + the length of the DER-encoded Digest Info.
   *
   * And a DigestInfo is 34 octets for md5, and 35 octets for sha1.
   * 46 octets is 368 bits. */
  
  if (size < 46)
    {
      /* Make sure the signing and verification functions doesn't
       * try to use this key. */
      key->size = 0;

      return 0;
    }
  else
    {
      key->size = size;
      return 1;
    }
}

int
rsa_prepare_private_key(struct rsa_private_key *key)
{
  return rsa_prepare_public_key(&key->pub);
}