Commit 2b0180c3 authored by Adam Langley's avatar Adam Langley Committed by Ben Laurie
Browse files

Ensure that x**0 mod 1 = 0.

parent 7753a3a6

crypto/bn/bn_exp.c

+8 −1
Original line number Diff line number Diff line
@@ -980,6 +980,13 @@ int BN_mod_exp_mont_word(BIGNUM *rr, BN_ULONG a, const BIGNUM *p, 
	bits = BN_num_bits(p);

	if (bits == 0)

		{

		/* x**0 mod 1 is still zero. */

		if (BN_is_one(m))

			{

			ret = 1;

			BN_zero(rr);

			}

		else

			ret = BN_one(rr);

		return ret;

		}

crypto/bn/exptest.c

+44 −1
Original line number Diff line number Diff line
@@ -71,6 +71,43 @@ 


static const char rnd_seed[] = "string to make the random number generator think it has entropy";



/* test_exp_mod_zero tests that x**0 mod 1 == 0. It returns zero on success. */

static int test_exp_mod_zero() {

	BIGNUM a, p, m;

	BIGNUM r;

	BN_CTX *ctx = BN_CTX_new();

	int ret = 1;



	BN_init(&m);

	BN_one(&m);



	BN_init(&a);

	BN_one(&a);



	BN_init(&p);

	BN_zero(&p);



	BN_init(&r);

	BN_mod_exp(&r, &a, &p, &m, ctx);

	BN_CTX_free(ctx);



	if (BN_is_zero(&r))

		ret = 0;

	else

		{

		printf("1**0 mod 1 = ");

		BN_print_fp(stdout, &r);

		printf(", should be 0\n");

		}



	BN_free(&r);

	BN_free(&a);

	BN_free(&p);

	BN_free(&m);



	return ret;

}



int main(int argc, char *argv[])

	{

	BN_CTX *ctx;
@@ -190,7 +227,13 @@ int main(int argc, char *argv[]) 
	ERR_remove_thread_state(NULL);

	CRYPTO_mem_leaks(out);

	BIO_free(out);

	printf("\n");



	if (test_exp_mod_zero() != 0)

		goto err;



	printf("done\n");



	EXIT(0);

err:

	ERR_load_crypto_strings();