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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_encrypt_last.c
OCB implementation, internal helper, by Karel Miko
*/
#include "tomcrypt.h"
#ifdef LTC_OCB3_MODE
/**
Finish an OCB (encryption) stream
@param ocb The OCB state
@param pt The remaining plaintext
@param ptlen The length of the plaintext (octets)
@param ct [out] The output buffer
@return CRYPT_OK if successful
*/
int ocb3_encrypt_last(ocb3_state *ocb, const unsigned char *pt, unsigned long ptlen, unsigned char *ct)
{
unsigned char iOffset_star[MAXBLOCKSIZE];
unsigned char iPad[MAXBLOCKSIZE];
int err, x, full_blocks, full_blocks_len, last_block_len;
LTC_ARGCHK(ocb != NULL);
if (pt == NULL) LTC_ARGCHK(ptlen == 0);
if (ptlen != 0) {
LTC_ARGCHK(pt != NULL);
LTC_ARGCHK(ct != NULL);
}
if ((err = cipher_is_valid(ocb->cipher)) != CRYPT_OK) {
goto LBL_ERR;
}
full_blocks = ptlen/ocb->block_len;
full_blocks_len = full_blocks * ocb->block_len;
last_block_len = ptlen - full_blocks_len;
/* process full blocks first */
if (full_blocks>0) {
if ((err = ocb3_encrypt(ocb, pt, full_blocks_len, ct)) != CRYPT_OK) {
goto LBL_ERR;
}
}
/* at this point: m = ocb->block_index (last block index), Offset_m = ocb->Offset_current */
if (last_block_len>0) {
/* Offset_* = Offset_m xor L_* */
ocb3_int_xor_blocks(iOffset_star, ocb->Offset_current, ocb->L_star, ocb->block_len);
/* Pad = ENCIPHER(K, Offset_*) */
if ((err = cipher_descriptor[ocb->cipher].ecb_encrypt(iOffset_star, iPad, &ocb->key)) != CRYPT_OK) {
goto LBL_ERR;
}
/* C_* = P_* xor Pad[1..bitlen(P_*)] */
ocb3_int_xor_blocks(ct+full_blocks_len, pt+full_blocks_len, iPad, last_block_len);
/* Checksum_* = Checksum_m xor (P_* || 1 || zeros(127-bitlen(P_*))) */
ocb3_int_xor_blocks(ocb->checksum, ocb->checksum, pt+full_blocks_len, last_block_len);
for(x=last_block_len; x<ocb->block_len; x++) {
if (x == last_block_len)
ocb->checksum[x] ^= 0x80;
else
ocb->checksum[x] ^= 0x00;
}
/* Tag = ENCIPHER(K, Checksum_* xor Offset_* xor L_$) xor HASH(K,A) */
/* at this point we calculate only: Tag_part = ENCIPHER(K, Checksum_* xor Offset_* xor L_$) */
for(x=0; x<ocb->block_len; x++) {
ocb->tag_part[x] = (ocb->checksum[x] ^ iOffset_star[x]) ^ ocb->L_dollar[x];
}
if ((err = cipher_descriptor[ocb->cipher].ecb_encrypt(ocb->tag_part, ocb->tag_part, &ocb->key)) != CRYPT_OK) {
goto LBL_ERR;
}
}
else {
/* Tag = ENCIPHER(K, Checksum_m xor Offset_m xor L_$) xor HASH(K,A) */
/* at this point we calculate only: Tag_part = ENCIPHER(K, Checksum_m xor Offset_m xor L_$) */
for(x=0; x<ocb->block_len; x++) {
ocb->tag_part[x] = (ocb->checksum[x] ^ ocb->Offset_current[x]) ^ ocb->L_dollar[x];
}
if ((err = cipher_descriptor[ocb->cipher].ecb_encrypt(ocb->tag_part, ocb->tag_part, &ocb->key)) != CRYPT_OK) {
goto LBL_ERR;
}
}
err = CRYPT_OK;
LBL_ERR:
#ifdef LTC_CLEAN_STACK
zeromem(iOffset_star, MAXBLOCKSIZE);
zeromem(iPad, MAXBLOCKSIZE);
#endif
return err;
}
#endif
/* ref: $Format:%D$ */
/* git commit: $Format:%H$ */
/* commit time: $Format:%ai$ */
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