/***************************************************************************
 *   Copyright (C) 2010 by Michael Fischer                                 *
 *   fischer-michael@cs.yale.edu                                           *
 *                                                                         *
 *   For use in Yale course CPSC 467b, Spring 2010                         *
 ***************************************************************************/

// Compute a^b (mod c) using openssl BN library
// usage:  modexp-ssl a b c

#include <stdio.h>
#include <openssl/bn.h>
#include <openssl/crypto.h>
#include "stopwatch.h"

// ----------------------------------------------------------------------------
int main(int argc, char* argv[]) {
	stopwatch watch;

	if (argc != 4) {
		fprintf(stderr, "usage: %s a b c\n", argv[0]);
		return 1;
	}

	// Start timing
	startTime(&watch);

	BIGNUM* a = BN_new();
	BIGNUM* b = BN_new();
	BIGNUM* c = BN_new();
	BIGNUM* d = BN_new();

	int ret;
	ret = BN_dec2bn(&a, argv[1]);
	ret = BN_dec2bn(&b, argv[2]);
	ret = BN_dec2bn(&c, argv[3]);

	BN_CTX *ctx = BN_CTX_new();
	ret = BN_mod_exp(d, a, b, c, ctx);
	BN_CTX_free(ctx);

	char* s;
	s = BN_bn2dec(d);
	puts(s);
	OPENSSL_free( s );

	BN_free(a);
	BN_free(b);
	BN_free(c);
	BN_free(d);

	// Stop timing
	stopTime(&watch);

	// Print timing results
	printElapsedTime(&watch);
}