summaryrefslogtreecommitdiffstats
path: root/libtommath/bn_mp_prime_miller_rabin.c
diff options
context:
space:
mode:
authorKevin B Kenny <kennykb@acm.org>2005-01-19 22:41:26 (GMT)
committerKevin B Kenny <kennykb@acm.org>2005-01-19 22:41:26 (GMT)
commitb9cf65a08e6a59e434685e894e3189c201ac6791 (patch)
tree1f0868ef44c9f17d83d10dc94343df7b8cfe1842 /libtommath/bn_mp_prime_miller_rabin.c
parentc6a259aeeca4814a97cf6694814c63e74e4e18fa (diff)
downloadtcl-b9cf65a08e6a59e434685e894e3189c201ac6791.zip
tcl-b9cf65a08e6a59e434685e894e3189c201ac6791.tar.gz
tcl-b9cf65a08e6a59e434685e894e3189c201ac6791.tar.bz2
Import of libtommath 0.33
Diffstat (limited to 'libtommath/bn_mp_prime_miller_rabin.c')
-rw-r--r--libtommath/bn_mp_prime_miller_rabin.c99
1 files changed, 99 insertions, 0 deletions
diff --git a/libtommath/bn_mp_prime_miller_rabin.c b/libtommath/bn_mp_prime_miller_rabin.c
new file mode 100644
index 0000000..758a2c3
--- /dev/null
+++ b/libtommath/bn_mp_prime_miller_rabin.c
@@ -0,0 +1,99 @@
+#include <tommath.h>
+#ifdef BN_MP_PRIME_MILLER_RABIN_C
+/* LibTomMath, multiple-precision integer library -- Tom St Denis
+ *
+ * LibTomMath is a library that provides multiple-precision
+ * integer arithmetic as well as number theoretic functionality.
+ *
+ * The library was designed directly after the MPI library by
+ * Michael Fromberger but has been written from scratch with
+ * additional optimizations in place.
+ *
+ * The library is free for all purposes without any express
+ * guarantee it works.
+ *
+ * Tom St Denis, tomstdenis@iahu.ca, http://math.libtomcrypt.org
+ */
+
+/* Miller-Rabin test of "a" to the base of "b" as described in
+ * HAC pp. 139 Algorithm 4.24
+ *
+ * Sets result to 0 if definitely composite or 1 if probably prime.
+ * Randomly the chance of error is no more than 1/4 and often
+ * very much lower.
+ */
+int mp_prime_miller_rabin (mp_int * a, mp_int * b, int *result)
+{
+ mp_int n1, y, r;
+ int s, j, err;
+
+ /* default */
+ *result = MP_NO;
+
+ /* ensure b > 1 */
+ if (mp_cmp_d(b, 1) != MP_GT) {
+ return MP_VAL;
+ }
+
+ /* get n1 = a - 1 */
+ if ((err = mp_init_copy (&n1, a)) != MP_OKAY) {
+ return err;
+ }
+ if ((err = mp_sub_d (&n1, 1, &n1)) != MP_OKAY) {
+ goto LBL_N1;
+ }
+
+ /* set 2**s * r = n1 */
+ if ((err = mp_init_copy (&r, &n1)) != MP_OKAY) {
+ goto LBL_N1;
+ }
+
+ /* count the number of least significant bits
+ * which are zero
+ */
+ s = mp_cnt_lsb(&r);
+
+ /* now divide n - 1 by 2**s */
+ if ((err = mp_div_2d (&r, s, &r, NULL)) != MP_OKAY) {
+ goto LBL_R;
+ }
+
+ /* compute y = b**r mod a */
+ if ((err = mp_init (&y)) != MP_OKAY) {
+ goto LBL_R;
+ }
+ if ((err = mp_exptmod (b, &r, a, &y)) != MP_OKAY) {
+ goto LBL_Y;
+ }
+
+ /* if y != 1 and y != n1 do */
+ if (mp_cmp_d (&y, 1) != MP_EQ && mp_cmp (&y, &n1) != MP_EQ) {
+ j = 1;
+ /* while j <= s-1 and y != n1 */
+ while ((j <= (s - 1)) && mp_cmp (&y, &n1) != MP_EQ) {
+ if ((err = mp_sqrmod (&y, a, &y)) != MP_OKAY) {
+ goto LBL_Y;
+ }
+
+ /* if y == 1 then composite */
+ if (mp_cmp_d (&y, 1) == MP_EQ) {
+ goto LBL_Y;
+ }
+
+ ++j;
+ }
+
+ /* if y != n1 then composite */
+ if (mp_cmp (&y, &n1) != MP_EQ) {
+ goto LBL_Y;
+ }
+ }
+
+ /* probably prime now */
+ *result = MP_YES;
+LBL_Y:mp_clear (&y);
+LBL_R:mp_clear (&r);
+LBL_N1:mp_clear (&n1);
+ return err;
+}
+#endif