/* 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@iahu.ca, http://libtomcrypt.org *//* OCB Implementation by Tom St Denis */#include "mycrypt.h"#ifdef OCB_MODEint ocb_decrypt(ocb_state *ocb, const unsigned char *ct, unsigned char *pt){   unsigned char Z[MAXBLOCKSIZE], tmp[MAXBLOCKSIZE];   int err, x;   _ARGCHK(ocb != NULL);   _ARGCHK(pt  != NULL);   _ARGCHK(ct  != NULL);   /* check if valid cipher */   if ((err = cipher_is_valid(ocb->cipher)) != CRYPT_OK) {      return err;   }   _ARGCHK(cipher_descriptor[ocb->cipher].ecb_decrypt != NULL);      /* check length */   if (ocb->block_len != cipher_descriptor[ocb->cipher].block_length) {      return CRYPT_INVALID_ARG;   }   /* Get Z[i] value */   ocb_shift_xor(ocb, Z);   /* xor ct in, encrypt, xor Z out */   for (x = 0; x < ocb->block_len; x++) {       tmp[x] = ct[x] ^ Z[x];   }   cipher_descriptor[ocb->cipher].ecb_decrypt(tmp, pt, &ocb->key);   for (x = 0; x < ocb->block_len; x++) {       pt[x] ^= Z[x];   }   /* compute checksum */   for (x = 0; x < ocb->block_len; x++) {       ocb->checksum[x] ^= pt[x];   }#ifdef CLEAN_STACK   zeromem(Z, sizeof(Z));   zeromem(tmp, sizeof(tmp));#endif   return CRYPT_OK;}#endif