CVE-2016-1938-nss-mp_exptmod.c

/* Example code for bug CVE-2016-1938 in mp_exptmod()
 * author: Hanno Böck, license: CC0 / public domain
 *
 * This shows that a bug in the mp_div() function of nss can also produce wrong results
 * in mp_exptmod().
 * Two calculations are compared: Directly calling mp_exptmod() and calling mp_expt()
 * and mp_mod() separately. A correct implementation should always produce the same
 * result.
 */

#define MP_IOFUNC 1
#include <mpi/mpi.h>

#define MI "0F0F0F0F0F0F0F0F0F0F0F0F0F0F0F0F0F0F0F0F0F0F0F0F0F0F0F0F0F0F0F0F0F0F0F0F0F0EED0F0F0F0F0F0F0F0F0F0F0F0F0F0F0F0F0F0F0F0F0F0F0F0F0F0F0F7C000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
#define AI "80"
#define BI "fc"

int main()
{
	mp_int an, bn, mn, r1, r2, xn;

	mp_init(&an);
	mp_init(&bn);
	mp_init(&mn);
	mp_init(&r1);
	mp_init(&xn);
	mp_init(&r2);

	mp_read_radix(&an, AI, 16);
	mp_read_radix(&bn, BI, 16);
	mp_read_radix(&mn, MI, 16);

	mp_exptmod(&an, &bn, &mn, &r2);
	mp_expt(&an, &bn, &xn);
	mp_mod(&xn, &mn, &r1);

	mp_print(&r1, stdout);
	printf("\n");

	mp_print(&r2, stdout);
	printf("\n");

	if (mp_cmp(&r1, &r2) != 0)
		printf("results don't match\n");
	else
		printf("results match\n");

	mp_clear(&an);
	mp_clear(&bn);
	mp_clear(&mn);
	mp_clear(&r1);
	mp_clear(&r2);
	mp_clear(&xn);

	return 0;
}