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/* 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://libtomcrypt.org
*/
/**
@file gcm_done.c
GCM implementation, Terminate the stream, by Tom St Denis
*/
#include "tomcrypt.h"
#ifdef GCM_MODE
/**
Terminate a GCM stream
@param gcm The GCM state
@param tag [out] The destination for the MAC tag
@param taglen [in/out] The length of the MAC tag
@return CRYPT_OK on success
*/
int gcm_done(gcm_state *gcm,
unsigned char *tag, unsigned long *taglen)
{
unsigned long x;
int err;
LTC_ARGCHK(gcm != NULL);
LTC_ARGCHK(tag != NULL);
LTC_ARGCHK(taglen != NULL);
if (gcm->buflen > 16 || gcm->buflen < 0) {
return CRYPT_INVALID_ARG;
}
if ((err = cipher_is_valid(gcm->cipher)) != CRYPT_OK) {
return err;
}
if (gcm->mode != GCM_MODE_TEXT) {
return CRYPT_INVALID_ARG;
}
/* handle remaining ciphertext */
if (gcm->buflen) {
gcm->pttotlen += gcm->buflen * CONST64(8);
gcm_mult_h(gcm, gcm->X);
}
/* length */
STORE64H(gcm->totlen, gcm->buf);
STORE64H(gcm->pttotlen, gcm->buf+8);
for (x = 0; x < 16; x++) {
gcm->X[x] ^= gcm->buf[x];
}
gcm_mult_h(gcm, gcm->X);
/* encrypt original counter */
cipher_descriptor[gcm->cipher].ecb_encrypt(gcm->Y_0, gcm->buf, &gcm->K);
for (x = 0; x < 16 && x < *taglen; x++) {
tag[x] = gcm->buf[x] ^ gcm->X[x];
}
*taglen = x;
cipher_descriptor[gcm->cipher].done(&gcm->K);
return CRYPT_OK;
}
#endif
/* $Source: /cvs/libtom/libtomcrypt/src/encauth/gcm/gcm_done.c,v $ */
/* $Revision: 1.7 $ */
/* $Date: 2005/05/05 14:35:58 $ */
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