/* 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 *//* EAX Implementation by Tom St Denis */#include "mycrypt.h"#ifdef EAX_MODEint eax_init(eax_state *eax, int cipher, const unsigned char *key, unsigned long keylen,             const unsigned char *nonce, unsigned long noncelen,             const unsigned char *header, unsigned long headerlen){   unsigned char buf[MAXBLOCKSIZE];   int           err, blklen;   omac_state    omac;   unsigned long len;   _ARGCHK(eax   != NULL);   _ARGCHK(key   != NULL);   _ARGCHK(nonce != NULL);   if (headerlen > 0) {      _ARGCHK(header != NULL);   }   if ((err = cipher_is_valid(cipher)) != CRYPT_OK) {      return err;   }   blklen = cipher_descriptor[cipher].block_length;   /* N = OMAC_0K(nonce) */   zeromem(buf, sizeof(buf));   if ((err = omac_init(&omac, cipher, key, keylen)) != CRYPT_OK) {      return err;   }   /* omac the [0]_n */   if ((err = omac_process(&omac, buf, blklen)) != CRYPT_OK) {      return err;   }   /* omac the nonce */   if ((err = omac_process(&omac, nonce, noncelen)) != CRYPT_OK) {      return err;   }   /* store result */   len = sizeof(eax->N);   if ((err = omac_done(&omac, eax->N, &len)) != CRYPT_OK) {      return err;   }   /* H = OMAC_1K(header) */   zeromem(buf, sizeof(buf));   buf[blklen - 1] = 1;   if ((err = omac_init(&eax->headeromac, cipher, key, keylen)) != CRYPT_OK) {      return err;   }   /* omac the [1]_n */   if ((err = omac_process(&eax->headeromac, buf, blklen)) != CRYPT_OK) {      return err;   }   /* omac the header */   if (headerlen != 0) {      if ((err = omac_process(&eax->headeromac, header, headerlen)) != CRYPT_OK) {         return err;      }   }   /* note we don't finish the headeromac, this allows us to add more header later */   /* setup the CTR mode */   if ((err = ctr_start(cipher, eax->N, key, keylen, 0, &eax->ctr)) != CRYPT_OK) {      return err;   }   /* use big-endian counter */   eax->ctr.mode = 1;   /* setup the OMAC for the ciphertext */   if ((err = omac_init(&eax->ctomac, cipher, key, keylen)) != CRYPT_OK) {       return err;   }   /* omac [2]_n */   zeromem(buf, sizeof(buf));   buf[blklen-1] = 2;   if ((err = omac_process(&eax->ctomac, buf, blklen)) != CRYPT_OK) {      return err;   }#ifdef CLEAN_STACK   zeromem(buf, sizeof(buf));   zeromem(&omac, sizeof(omac));#endif   return CRYPT_OK;}#endif