Command line app to call openssl primality check

prime-test.c

/* Copyright (C) 2019 Karim Kanso. All Rights Reserved.
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program 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 General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */



/* Trivial program to call the openssl primality check from the
 * command line.
 *
 * Usage, pass prime number to test as first parameter on command
 * line.
 *
 * Exit code:
 *  2 - Error
 *  1 - Is Prime
 *  0 - Not Prime
 *
 * Compile:
 *  gcc -Wall -Wpedantic -c prime-test.c -o prime-test.o
 *  gcc prime-test.o -lcrypto -o prime-test
 */

#include <stdio.h>
#include <string.h>
#include <openssl/bn.h>

int main(int argc, char** argv) {
  if (argc != 2) {
    fputs("usage: provide the prime number as sole argument\n", stderr);
    return 1;
  }

  int i_ret = 2;
  BIGNUM *p_bn = BN_new();
  BN_CTX *p_bn_ctx = BN_CTX_new();

  if (BN_dec2bn(&p_bn, argv[1]) != strlen(argv[1])) {
    fputs("bad integer\n", stderr);
    goto cleanup;
  }

  int i_bits =  BN_num_bits(p_bn);
  switch (BN_is_prime_ex(p_bn, i_bits / 2, p_bn_ctx, NULL)) {
  case -1:
    fputs("prime check failed\n", stderr);
    break;
  case 1:
    fputs("is prime\n", stdout);
    i_ret = 0;
    break;
  case 0:
    fputs("not prime\n", stdout);
    i_ret = 1;
    break;
  default:
    fputs("internal error\n", stderr);
    break;
  }

 cleanup:
  BN_free(p_bn);
  p_bn = NULL;
  BN_CTX_free(p_bn_ctx);
  p_bn_ctx = NULL;
  return i_ret;
}