1 files changed, 86 insertions, 0 deletions
diff --git a/src/ltc/encauth/ocb3/ocb3_decrypt.c b/src/ltc/encauth/ocb3/ocb3_decrypt.c
new file mode 100644
index 00000000..24d6ad15
--- /dev/null
+++ b/src/ltc/encauth/ocb3/ocb3_decrypt.c
@@ -0,0 +1,86 @@
+/* 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, tomstdenis@gmail.com, http://libtom.org
+ */
+
+/**
+   @file ocb3_decrypt.c
+   OCB implementation, decrypt data, by Tom St Denis
+*/
+#include "tomcrypt.h"
+
+#ifdef LTC_OCB3_MODE
+
+/**
+   Decrypt blocks of ciphertext with OCB
+   @param ocb     The OCB state
+   @param ct      The ciphertext (length multiple of the block size of the block cipher)
+   @param ctlen   The length of the input (octets)
+   @param pt      [out] The plaintext (length of ct)
+   @return CRYPT_OK if successful
+*/
+int ocb3_decrypt(ocb3_state *ocb, const unsigned char *ct, unsigned long ctlen, unsigned char *pt)
+{
+   unsigned char tmp[MAXBLOCKSIZE];
+   int err, i, full_blocks;
+   unsigned char *pt_b, *ct_b;
+
+   LTC_ARGCHK(ocb != NULL);
+   LTC_ARGCHK(pt  != NULL);
+   LTC_ARGCHK(ct  != NULL);
+   if ((err = cipher_is_valid(ocb->cipher)) != CRYPT_OK) {
+      return err;
+   }
+   if (ocb->block_len != cipher_descriptor[ocb->cipher].block_length) {
+      return CRYPT_INVALID_ARG;
+   }
+
+   if (ctlen % ocb->block_len) { /* ctlen has to bu multiple of block_len */
+      return CRYPT_INVALID_ARG;
+   }
+
+   full_blocks = ctlen/ocb->block_len;
+   for(i=0; i<full_blocks; i++) {
+     pt_b = (unsigned char *)pt+i*ocb->block_len;
+     ct_b = (unsigned char *)ct+i*ocb->block_len;
+
+     /* ocb->Offset_current[] = ocb->Offset_current[] ^ Offset_{ntz(block_index)} */
+     ocb3_int_xor_blocks(ocb->Offset_current, ocb->Offset_current, ocb->L_[ocb3_int_ntz(ocb->block_index)], ocb->block_len);
+
+     /* tmp[] = ct[] XOR ocb->Offset_current[] */
+     ocb3_int_xor_blocks(tmp, ct_b, ocb->Offset_current, ocb->block_len);
+
+     /* decrypt */
+     if ((err = cipher_descriptor[ocb->cipher].ecb_decrypt(tmp, tmp, &ocb->key)) != CRYPT_OK) {
+        goto LBL_ERR;
+     }
+
+     /* pt[] = tmp[] XOR ocb->Offset_current[] */
+     ocb3_int_xor_blocks(pt_b, tmp, ocb->Offset_current, ocb->block_len);
+
+     /* ocb->checksum[] = ocb->checksum[] XOR pt[] */
+     ocb3_int_xor_blocks(ocb->checksum, ocb->checksum, pt_b, ocb->block_len);
+
+     ocb->block_index++;
+   }
+
+   err = CRYPT_OK;
+
+LBL_ERR:
+#ifdef LTC_CLEAN_STACK
+   zeromem(tmp, sizeof(tmp));
+#endif
+   return err;
+}
+
+#endif
+
+/* $Source$ */
+/* $Revision$ */
+/* $Date$ */