summaryrefslogtreecommitdiffstats
path: root/libtommath/bn_mp_prime_fermat.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_fermat.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_fermat.c')
-rw-r--r--libtommath/bn_mp_prime_fermat.c58
1 files changed, 58 insertions, 0 deletions
diff --git a/libtommath/bn_mp_prime_fermat.c b/libtommath/bn_mp_prime_fermat.c
new file mode 100644
index 0000000..fd74dbe
--- /dev/null
+++ b/libtommath/bn_mp_prime_fermat.c
@@ -0,0 +1,58 @@
+#include <tommath.h>
+#ifdef BN_MP_PRIME_FERMAT_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
+ */
+
+/* performs one Fermat test.
+ *
+ * If "a" were prime then b**a == b (mod a) since the order of
+ * the multiplicative sub-group would be phi(a) = a-1. That means
+ * it would be the same as b**(a mod (a-1)) == b**1 == b (mod a).
+ *
+ * Sets result to 1 if the congruence holds, or zero otherwise.
+ */
+int mp_prime_fermat (mp_int * a, mp_int * b, int *result)
+{
+ mp_int t;
+ int err;
+
+ /* default to composite */
+ *result = MP_NO;
+
+ /* ensure b > 1 */
+ if (mp_cmp_d(b, 1) != MP_GT) {
+ return MP_VAL;
+ }
+
+ /* init t */
+ if ((err = mp_init (&t)) != MP_OKAY) {
+ return err;
+ }
+
+ /* compute t = b**a mod a */
+ if ((err = mp_exptmod (b, a, a, &t)) != MP_OKAY) {
+ goto LBL_T;
+ }
+
+ /* is it equal to b? */
+ if (mp_cmp (&t, b) == MP_EQ) {
+ *result = MP_YES;
+ }
+
+ err = MP_OKAY;
+LBL_T:mp_clear (&t);
+ return err;
+}
+#endif