invmod.c

来自「支持SSL v2/v3, TLS, PKCS #5, PKCS #7, PKCS」· C语言 代码 · 共 90 行

/*
 *  invmod.c
 *
 *  Compute modular inverses
 *
 * The contents of this file are subject to the Mozilla Public
 * License Version 1.1 (the "License"); you may not use this file
 * except in compliance with the License. You may obtain a copy of
 * the License at http://www.mozilla.org/MPL/
 *
 * Software distributed under the License is distributed on an "AS
 * IS" basis, WITHOUT WARRANTY OF ANY KIND, either express or
 * implied. See the License for the specific language governing
 * rights and limitations under the License.
 *
 * The Original Code is the MPI Arbitrary Precision Integer Arithmetic
 * library.
 *
 * The Initial Developer of the Original Code is Michael J. Fromberger.
 * Portions created by Michael J. Fromberger are 
 * Copyright (C) 1997, 1998, 1999, 2000 Michael J. Fromberger. 
 * All Rights Reserved.
 *
 * Contributor(s):
 *
 * Alternatively, the contents of this file may be used under the
 * terms of the GNU General Public License Version 2 or later (the
 * "GPL"), in which case the provisions of the GPL are applicable
 * instead of those above.  If you wish to allow use of your
 * version of this file only under the terms of the GPL and not to
 * allow others to use your version of this file under the MPL,
 * indicate your decision by deleting the provisions above and
 * replace them with the notice and other provisions required by
 * the GPL.  If you do not delete the provisions above, a recipient
 * may use your version of this file under either the MPL or the GPL.
 *
 *  $Id: invmod.c,v 1.1 2000/07/14 00:44:57 nelsonb%netscape.com Exp $
 */

#include <stdio.h>
#include <stdlib.h>

#include "mpi.h"

int main(int argc, char *argv[])
{
  mp_int    a, m;
  mp_err    res;
  char     *buf;
  int       len, out = 0;

  if(argc < 3) {
    fprintf(stderr, "Usage: %s <a> <m>\n", argv[0]);
    return 1;
  }

  mp_init(&a); mp_init(&m);
  mp_read_radix(&a, argv[1], 10);
  mp_read_radix(&m, argv[2], 10);

  if(mp_cmp(&a, &m) > 0)
    mp_mod(&a, &m, &a);

  switch((res = mp_invmod(&a, &m, &a))) {
  case MP_OKAY:
    len = mp_radix_size(&a, 10);
    buf = malloc(len);

    mp_toradix(&a, buf, 10);
    printf("%s\n", buf);
    free(buf);
    break;

  case MP_UNDEF:
    printf("No inverse\n");
    out = 1;
    break;

  default:
    printf("error: %s (%d)\n", mp_strerror(res), res);
    out = 2;
    break;
  }

  mp_clear(&a);
  mp_clear(&m);

  return out;
}