--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/libtomcrypt/src/pk/katja/katja_exptmod.c	Sat Feb 03 08:20:34 2007 +0000
@@ -0,0 +1,115 @@
+/* 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.com
+ */
+#include "tomcrypt.h"
+
+/**
+  @file katja_exptmod.c
+  Katja PKCS-style exptmod, Tom St Denis
+*/  
+
+#ifdef MKAT
+
+/** 
+   Compute an RSA modular exponentiation 
+   @param in         The input data to send into RSA
+   @param inlen      The length of the input (octets)
+   @param out        [out] The destination 
+   @param outlen     [in/out] The max size and resulting size of the output
+   @param which      Which exponent to use, e.g. PK_PRIVATE or PK_PUBLIC
+   @param key        The RSA key to use 
+   @return CRYPT_OK if successful
+*/   
+int katja_exptmod(const unsigned char *in,   unsigned long inlen,
+                        unsigned char *out,  unsigned long *outlen, int which,
+                        katja_key *key)
+{
+   void         *tmp, *tmpa, *tmpb;
+   unsigned long x;
+   int           err;
+
+   LTC_ARGCHK(in     != NULL);
+   LTC_ARGCHK(out    != NULL);
+   LTC_ARGCHK(outlen != NULL);
+   LTC_ARGCHK(key    != NULL);
+  
+   /* is the key of the right type for the operation? */
+   if (which == PK_PRIVATE && (key->type != PK_PRIVATE)) {
+      return CRYPT_PK_NOT_PRIVATE;
+   }
+
+   /* must be a private or public operation */
+   if (which != PK_PRIVATE && which != PK_PUBLIC) {
+      return CRYPT_PK_INVALID_TYPE;
+   }
+
+   /* init and copy into tmp */
+   if ((err = mp_init_multi(&tmp, &tmpa, &tmpb, NULL)) != CRYPT_OK)                                    { return err; }
+   if ((err = mp_read_unsigned_bin(tmp, (unsigned char *)in, (int)inlen)) != CRYPT_OK)                 { goto error; }
+
+   /* sanity check on the input */
+   if (mp_cmp(key->N, tmp) == LTC_MP_LT) {
+      err = CRYPT_PK_INVALID_SIZE;
+      goto done;
+   }
+
+   /* are we using the private exponent and is the key optimized? */
+   if (which == PK_PRIVATE) {
+      /* tmpa = tmp^dP mod p */
+      if ((err = mp_exptmod(tmp, key->dP, key->p, tmpa)) != CRYPT_OK)                               { goto error; }
+
+      /* tmpb = tmp^dQ mod q */
+      if ((err = mp_exptmod(tmp, key->dQ, key->q, tmpb)) != CRYPT_OK)                               { goto error; }
+
+      /* tmp = (tmpa - tmpb) * qInv (mod p) */
+      if ((err = mp_sub(tmpa, tmpb, tmp)) != CRYPT_OK)                                              { goto error; }
+      if ((err = mp_mulmod(tmp, key->qP, key->p, tmp)) != CRYPT_OK)                                 { goto error; }
+
+      /* tmp = tmpb + q * tmp */
+      if ((err = mp_mul(tmp, key->q, tmp)) != CRYPT_OK)                                             { goto error; }
+      if ((err = mp_add(tmp, tmpb, tmp)) != CRYPT_OK)                                               { goto error; }
+   } else {
+      /* exptmod it */
+      if ((err = mp_exptmod(tmp, key->N, key->N, tmp)) != CRYPT_OK)                                 { goto error; }
+   }
+
+   /* read it back */
+   x = (unsigned long)mp_unsigned_bin_size(key->N);
+   if (x > *outlen) {
+      *outlen = x;
+      err = CRYPT_BUFFER_OVERFLOW;
+      goto done;
+   }
+
+   /* this should never happen ... */
+   if (mp_unsigned_bin_size(tmp) > mp_unsigned_bin_size(key->N)) {
+      err = CRYPT_ERROR;
+      goto done;
+   }
+   *outlen = x;
+
+   /* convert it */
+   zeromem(out, x);
+   if ((err = mp_to_unsigned_bin(tmp, out+(x-mp_unsigned_bin_size(tmp)))) != CRYPT_OK)               { goto error; }
+
+   /* clean up and return */
+   err = CRYPT_OK;
+   goto done;
+error:
+done:
+   mp_clear_multi(tmp, tmpa, tmpb, NULL);
+   return err;
+}
+
+#endif
+
+/* $Source: /cvs/libtom/libtomcrypt/src/pk/katja/katja_exptmod.c,v $ */
+/* $Revision: 1.5 $ */
+/* $Date: 2006/06/16 21:53:41 $ */