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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.
*/
/**
@file ocb3_done.c
OCB implementation, INTERNAL ONLY helper, by Tom St Denis
*/
#include "tomcrypt.h"
#ifdef LTC_OCB3_MODE
/**
Finish OCB processing and compute the tag
@param ocb The OCB state
@param tag [out] The destination for the authentication tag
@param taglen [in/out] The max size and resulting size of the authentication tag
@return CRYPT_OK if successful
*/
int ocb3_done(ocb3_state *ocb, unsigned char *tag, unsigned long *taglen)
{
unsigned char tmp[MAXBLOCKSIZE];
int err, x;
LTC_ARGCHK(ocb != NULL);
LTC_ARGCHK(tag != NULL);
LTC_ARGCHK(taglen != NULL);
if ((err = cipher_is_valid(ocb->cipher)) != CRYPT_OK) {
goto LBL_ERR;
}
/* check taglen */
if ((int)*taglen < ocb->tag_len) {
*taglen = (unsigned long)ocb->tag_len;
return CRYPT_BUFFER_OVERFLOW;
}
/* finalize AAD processing */
if (ocb->adata_buffer_bytes>0) {
/* Offset_* = Offset_m xor L_* */
ocb3_int_xor_blocks(ocb->aOffset_current, ocb->aOffset_current, ocb->L_star, ocb->block_len);
/* CipherInput = (A_* || 1 || zeros(127-bitlen(A_*))) xor Offset_* */
ocb3_int_xor_blocks(tmp, ocb->adata_buffer, ocb->aOffset_current, ocb->adata_buffer_bytes);
for(x=ocb->adata_buffer_bytes; x<ocb->block_len; x++) {
if (x == ocb->adata_buffer_bytes) {
tmp[x] = 0x80 ^ ocb->aOffset_current[x];
}
else {
tmp[x] = 0x00 ^ ocb->aOffset_current[x];
}
}
/* Sum = Sum_m xor ENCIPHER(K, CipherInput) */
if ((err = cipher_descriptor[ocb->cipher].ecb_encrypt(tmp, tmp, &ocb->key)) != CRYPT_OK) {
goto LBL_ERR;
}
ocb3_int_xor_blocks(ocb->aSum_current, ocb->aSum_current, tmp, ocb->block_len);
}
/* finalize TAG computing */
/* at this point ocb->aSum_current = HASH(K, A) */
/* tag = tag ^ HASH(K, A) */
ocb3_int_xor_blocks(tmp, ocb->tag_part, ocb->aSum_current, ocb->block_len);
/* copy tag bytes */
for(x = 0; x < ocb->tag_len; x++) tag[x] = tmp[x];
*taglen = (unsigned long)ocb->tag_len;
err = CRYPT_OK;
LBL_ERR:
#ifdef LTC_CLEAN_STACK
zeromem(tmp, MAXBLOCKSIZE);
zeromem(ocb, sizeof(*ocb));
#endif
return err;
}
#endif
/* ref: $Format:%D$ */
/* git commit: $Format:%H$ */
/* commit time: $Format:%ai$ */
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