--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/tim_exptmod.c	Tue Jun 15 14:07:21 2004 +0000
@@ -0,0 +1,77 @@
+/* LibTomCrypt, modular cryptographic library -- Tom St Denis
+ *
+ * LibTomCrypt is a library that provides various cryptographic
+ * algorithms in a highly modular and flexible manner.
+ *
+ * The library is free for all purposes without any express
+ * guarantee it works.
+ *
+ * Tom St Denis, [email protected], http://libtomcrypt.org
+ */
+
+/* RSA Code by Tom St Denis */
+#include "mycrypt.h"
+
+#ifdef RSA_TIMING
+
+/* decrypts c into m */
+int tim_exptmod(prng_state *prng, int prng_idx, 
+                mp_int *c, mp_int *e, mp_int *d, mp_int *n, mp_int *m)
+{
+   int           err;
+   mp_int        r, tmp, tmp2;
+   unsigned char *rtmp;
+   unsigned long rlen;
+
+   _ARGCHK(c != NULL);
+   _ARGCHK(e != NULL);
+   _ARGCHK(d != NULL);
+   _ARGCHK(n != NULL);
+   _ARGCHK(m != NULL);
+
+   if ((err = prng_is_valid(prng_idx)) != CRYPT_OK) {
+      return err;
+   }
+
+   /* pick random r */ 
+   rtmp = XMALLOC(MAX_RSA_SIZE/8);
+   if (rtmp == NULL) {
+      return CRYPT_MEM;
+   }
+
+
+   rlen = mp_unsigned_bin_size(n);
+   if (prng_descriptor[prng_idx].read(rtmp, rlen, prng) != rlen) {
+      XFREE(rtmp);
+      return CRYPT_ERROR_READPRNG;
+   }
+
+   if ((err = mp_init_multi(&r, &tmp, &tmp2, NULL)) != MP_OKAY) {
+      XFREE(rtmp);
+      return mpi_to_ltc_error(err);
+   }
+
+   /* read in r */
+   if ((err = mp_read_unsigned_bin(&r, rtmp, rlen)) != MP_OKAY)              { goto __ERR; }
+
+   /* compute tmp = r^e */
+   if ((err = mp_exptmod(&r, e, n, &tmp)) != MP_OKAY)                        { goto __ERR; }
+
+   /* multiply C into the mix */
+   if ((err = mp_mulmod(c, &tmp, n, &tmp)) != MP_OKAY)                       { goto __ERR; }
+
+   /* raise to d */
+   if ((err = mp_exptmod(&tmp, d, n, &tmp)) != MP_OKAY)                      { goto __ERR; }
+   
+   /* invert r and multiply */
+   if ((err = mp_invmod(&r, n, &tmp2)) != MP_OKAY)                           { goto __ERR; }
+
+   /* multiply and we are totally set */
+   if ((err = mp_mulmod(&tmp, &tmp2, n, m)) != MP_OKAY)                      { goto __ERR; }
+
+__ERR:  mp_clear_multi(&r, &tmp, &tmp2, NULL);
+   XFREE(rtmp);
+   return mpi_to_ltc_error(err);
+}
+
+#endif