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