--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/encauth/ocb/s_ocb_done.c	Fri May 06 13:23:02 2005 +0000
@@ -0,0 +1,140 @@
+/* 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
+ */
+
+/** 
+   @file s_ocb_done.c
+   OCB implementation, internal helper, by Tom St Denis
+*/
+#include "tomcrypt.h"
+
+#ifdef OCB_MODE
+
+/* Since the last block is encrypted in CTR mode the same code can
+ * be used to finish a decrypt or encrypt stream.  The only difference
+ * is we XOR the final ciphertext into the checksum so we have to xor it
+ * before we CTR [decrypt] or after [encrypt]
+ *
+ * the names pt/ptlen/ct really just mean in/inlen/out but this is the way I wrote it... 
+ */
+
+/**
+   Shared code to finish an OCB stream
+   @param ocb    The OCB state
+   @param pt     The remaining plaintext [or input]
+   @param ptlen  The length of the input (octets)
+   @param ct     [out] The output buffer
+   @param tag    [out] The destination for the authentication tag
+   @param taglen [in/out] The max size and resulting size of the authentication tag
+   @param mode   The mode we are terminating, 0==encrypt, 1==decrypt
+   @return       CRYPT_OK if successful
+*/
+int s_ocb_done(ocb_state *ocb, const unsigned char *pt, unsigned long ptlen,
+               unsigned char *ct, unsigned char *tag, unsigned long *taglen, int mode)
+
+{
+   unsigned char *Z, *Y, *X;
+   int err, x;
+
+   LTC_ARGCHK(ocb    != NULL);
+   LTC_ARGCHK(pt     != NULL);
+   LTC_ARGCHK(ct     != NULL);
+   LTC_ARGCHK(tag    != NULL);
+   LTC_ARGCHK(taglen != NULL);
+   if ((err = cipher_is_valid(ocb->cipher)) != CRYPT_OK) {
+      return err;
+   }
+   if (ocb->block_len != cipher_descriptor[ocb->cipher].block_length ||
+       (int)ptlen > ocb->block_len || (int)ptlen < 0) {
+      return CRYPT_INVALID_ARG;
+   }
+
+   /* allocate ram */
+   Z = XMALLOC(MAXBLOCKSIZE);
+   Y = XMALLOC(MAXBLOCKSIZE);
+   X = XMALLOC(MAXBLOCKSIZE);
+   if (X == NULL || Y == NULL || Z == NULL) {
+      if (X != NULL) {
+         XFREE(X);
+      }
+      if (Y != NULL) {
+         XFREE(Y);
+      }
+      if (Z != NULL) {
+         XFREE(Z);
+      }
+      return CRYPT_MEM;
+   }
+
+   /* compute X[m] = len(pt[m]) XOR Lr XOR Z[m] */
+   ocb_shift_xor(ocb, X); 
+   XMEMCPY(Z, X, ocb->block_len);
+
+   X[ocb->block_len-1] ^= (ptlen*8)&255;
+   X[ocb->block_len-2] ^= ((ptlen*8)>>8)&255;
+   for (x = 0; x < ocb->block_len; x++) {
+       X[x] ^= ocb->Lr[x]; 
+   }
+
+   /* Y[m] = E(X[m])) */
+   cipher_descriptor[ocb->cipher].ecb_encrypt(X, Y, &ocb->key);
+
+   if (mode == 1) {
+      /* decrypt mode, so let's xor it first */
+      /* xor C[m] into checksum */
+      for (x = 0; x < (int)ptlen; x++) {
+         ocb->checksum[x] ^= ct[x];
+      }  
+   }
+
+   /* C[m] = P[m] xor Y[m] */
+   for (x = 0; x < (int)ptlen; x++) {
+       ct[x] = pt[x] ^ Y[x];
+   }
+
+   if (mode == 0) {
+      /* encrypt mode */    
+      /* xor C[m] into checksum */
+      for (x = 0; x < (int)ptlen; x++) {
+          ocb->checksum[x] ^= ct[x];
+      }
+   }
+
+   /* xor Y[m] and Z[m] into checksum */
+   for (x = 0; x < ocb->block_len; x++) {
+       ocb->checksum[x] ^= Y[x] ^ Z[x];
+   }
+   
+   /* encrypt checksum, er... tag!! */
+   cipher_descriptor[ocb->cipher].ecb_encrypt(ocb->checksum, X, &ocb->key);
+   cipher_descriptor[ocb->cipher].done(&ocb->key);
+
+   /* now store it */
+   for (x = 0; x < ocb->block_len && x < (int)*taglen; x++) {
+       tag[x] = X[x];
+   }
+   *taglen = x;
+
+#ifdef LTC_CLEAN_STACK
+   zeromem(X, MAXBLOCKSIZE);
+   zeromem(Y, MAXBLOCKSIZE);
+   zeromem(Z, MAXBLOCKSIZE);
+   zeromem(ocb, sizeof(*ocb));
+#endif
+   
+   XFREE(X);
+   XFREE(Y);
+   XFREE(Z);
+
+   return CRYPT_OK;
+}
+
+#endif
+