81 lines
1.9 KiB
C
81 lines
1.9 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 gcm_done.c
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GCM implementation, Terminate the stream, by Tom St Denis
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*/
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#include "tomcrypt_private.h"
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#ifdef LTC_GCM_MODE
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/**
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Terminate a GCM stream
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@param gcm The GCM state
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@param tag [out] The destination for the MAC tag
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@param taglen [in/out] The length of the MAC tag
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@return CRYPT_OK on success
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*/
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int gcm_done(gcm_state *gcm,
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unsigned char *tag, unsigned long *taglen)
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{
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unsigned long x;
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int err;
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LTC_ARGCHK(gcm != NULL);
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LTC_ARGCHK(tag != NULL);
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LTC_ARGCHK(taglen != NULL);
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if (gcm->buflen > 16 || gcm->buflen < 0) {
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return CRYPT_INVALID_ARG;
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}
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if ((err = cipher_is_valid(gcm->cipher)) != CRYPT_OK) {
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return err;
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}
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if (gcm->mode == LTC_GCM_MODE_IV) {
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/* let's process the IV */
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if ((err = gcm_add_aad(gcm, NULL, 0)) != CRYPT_OK) return err;
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}
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if (gcm->mode == LTC_GCM_MODE_AAD) {
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/* let's process the AAD */
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if ((err = gcm_process(gcm, NULL, 0, NULL, 0)) != CRYPT_OK) return err;
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}
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if (gcm->mode != LTC_GCM_MODE_TEXT) {
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return CRYPT_INVALID_ARG;
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}
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/* handle remaining ciphertext */
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if (gcm->buflen) {
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gcm->pttotlen += gcm->buflen * CONST64(8);
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gcm_mult_h(gcm, gcm->X);
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}
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/* length */
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STORE64H(gcm->totlen, gcm->buf);
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STORE64H(gcm->pttotlen, gcm->buf+8);
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for (x = 0; x < 16; x++) {
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gcm->X[x] ^= gcm->buf[x];
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}
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gcm_mult_h(gcm, gcm->X);
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/* encrypt original counter */
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if ((err = cipher_descriptor[gcm->cipher].ecb_encrypt(gcm->Y_0, gcm->buf, &gcm->K)) != CRYPT_OK) {
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return err;
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}
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for (x = 0; x < 16 && x < *taglen; x++) {
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tag[x] = gcm->buf[x] ^ gcm->X[x];
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}
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*taglen = x;
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cipher_descriptor[gcm->cipher].done(&gcm->K);
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return CRYPT_OK;
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}
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#endif
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