--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/libtomcrypt/src/modes/xts/xts_decrypt.c	Sat Jun 24 17:50:50 2017 +0800
@@ -0,0 +1,141 @@
+/* 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://libtom.org
+ */
+#include "tomcrypt.h"
+
+/** 
+  Source donated by Elliptic Semiconductor Inc (www.ellipticsemi.com) to the LibTom Projects
+*/
+
+#ifdef LTC_XTS_MODE
+
+static int tweak_uncrypt(const unsigned char *C, unsigned char *P, unsigned char *T, symmetric_xts *xts)
+{
+   unsigned long x;
+   int err;
+
+   /* tweak encrypt block i */
+#ifdef LTC_FAST
+   for (x = 0; x < 16; x += sizeof(LTC_FAST_TYPE)) {
+      *((LTC_FAST_TYPE*)&P[x]) = *((LTC_FAST_TYPE*)&C[x]) ^ *((LTC_FAST_TYPE*)&T[x]);
+   }
+#else
+   for (x = 0; x < 16; x++) {
+       P[x] = C[x] ^ T[x];
+   }
+#endif
+     
+   err = cipher_descriptor[xts->cipher].ecb_decrypt(P, P, &xts->key1);  
+
+#ifdef LTC_FAST
+   for (x = 0; x < 16; x += sizeof(LTC_FAST_TYPE)) {
+      *((LTC_FAST_TYPE*)&P[x]) ^=  *((LTC_FAST_TYPE*)&T[x]);
+   }
+#else
+   for (x = 0; x < 16; x++) {
+       P[x] = P[x] ^ T[x];
+   }
+#endif
+
+   /* LFSR the tweak */
+   xts_mult_x(T);
+
+   return err;
+}   
+
+/** XTS Decryption
+  @param ct     [in] Ciphertext
+  @param ptlen  Length of plaintext (and ciphertext)
+  @param pt     [out]  Plaintext
+  @param tweak  [in] The 128--bit encryption tweak (e.g. sector number)
+  @param xts    The XTS structure
+  Returns CRYPT_OK upon success
+*/int xts_decrypt(
+   const unsigned char *ct, unsigned long ptlen,
+         unsigned char *pt,
+   const unsigned char *tweak,
+         symmetric_xts *xts)
+{
+   unsigned char PP[16], CC[16], T[16];
+   unsigned long i, m, mo, lim;
+   int           err;
+
+   /* check inputs */
+   LTC_ARGCHK(pt    != NULL);
+   LTC_ARGCHK(ct    != NULL);
+   LTC_ARGCHK(tweak != NULL);
+   LTC_ARGCHK(xts   != NULL);
+
+   /* check if valid */
+   if ((err = cipher_is_valid(xts->cipher)) != CRYPT_OK) {
+      return err;
+   }
+
+   /* get number of blocks */
+   m  = ptlen >> 4;
+   mo = ptlen & 15;
+
+   /* must have at least one full block */
+   if (m == 0) {
+      return CRYPT_INVALID_ARG;
+   }
+
+   /* encrypt the tweak */
+   if ((err = cipher_descriptor[xts->cipher].ecb_encrypt(tweak, T, &xts->key2)) != CRYPT_OK) {
+      return err;
+   }
+
+   /* for i = 0 to m-2 do */
+   if (mo == 0) {
+      lim = m;
+   } else {
+      lim = m - 1;
+   }
+
+   for (i = 0; i < lim; i++) {
+      err = tweak_uncrypt(ct, pt, T, xts);
+      ct += 16;
+      pt += 16;
+   }
+   
+   /* if ptlen not divide 16 then */
+   if (mo > 0) {
+      XMEMCPY(CC, T, 16);
+      xts_mult_x(CC);
+
+      /* PP = tweak decrypt block m-1 */
+      if ((err = tweak_uncrypt(ct, PP, CC, xts)) != CRYPT_OK) {
+         return err;
+      }
+
+      /* Pm = first ptlen % 16 bytes of PP */
+      for (i = 0; i < mo; i++) {
+          CC[i]    = ct[16+i];
+          pt[16+i] = PP[i];
+      }
+      for (; i < 16; i++) {
+          CC[i] = PP[i];
+      }
+
+      /* Pm-1 = Tweak uncrypt CC */
+      if ((err = tweak_uncrypt(CC, pt, T, xts)) != CRYPT_OK) {
+         return err;
+      }
+   }
+
+   return CRYPT_OK;
+}
+
+#endif
+
+/* $Source$ */
+/* $Revision$ */
+/* $Date$ */
+