--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/cbc_decrypt.c	Mon May 31 18:21:40 2004 +0000
@@ -0,0 +1,56 @@
+/* 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
+ */
+#include "mycrypt.h"
+
+#ifdef CBC
+
+int cbc_decrypt(const unsigned char *ct, unsigned char *pt, symmetric_CBC *cbc)
+{
+   int x, err;
+   unsigned char tmp[MAXBLOCKSIZE], tmp2[MAXBLOCKSIZE];
+
+   _ARGCHK(pt != NULL);
+   _ARGCHK(ct != NULL);
+   _ARGCHK(cbc != NULL);
+
+   /* decrypt the block from ct into tmp */
+   if ((err = cipher_is_valid(cbc->cipher)) != CRYPT_OK) {
+       return err;
+   }
+   cipher_descriptor[cbc->cipher].ecb_decrypt(ct, tmp, &cbc->key);
+   
+   /* is blocklen valid? */
+   if (cbc->blocklen < 0 || cbc->blocklen > (int)sizeof(cbc->IV)) {
+      return CRYPT_INVALID_ARG;
+   } 
+
+   /* xor IV against the plaintext of the previous step */
+   for (x = 0; x < cbc->blocklen; x++) { 
+       /* copy CT in case ct == pt */
+       tmp2[x] = ct[x]; 
+
+       /* actually decrypt the byte */
+       pt[x] = tmp[x] ^ cbc->IV[x]; 
+   }
+
+   /* replace IV with this current ciphertext */ 
+   for (x = 0; x < cbc->blocklen; x++) {
+       cbc->IV[x] = tmp2[x];
+   }
+   #ifdef CLEAN_STACK
+      zeromem(tmp, sizeof(tmp));
+      zeromem(tmp2, sizeof(tmp2));
+   #endif
+   return CRYPT_OK;
+}
+
+#endif
+