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/*
chronyd/chronyc - Programs for keeping computer clocks accurate.
**********************************************************************
* Copyright (C) Miroslav Lichvar 2020
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of version 2 of the GNU General Public License as
* published by the Free Software Foundation.
*
* This program is distributed in the hope that it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* General Public License for more details.
*
* You should have received a copy of the GNU General Public License along
* with this program; if not, write to the Free Software Foundation, Inc.,
* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
*
**********************************************************************
=======================================================================
NTS Authenticator and Encrypted Extension Fields extension field
*/
#include "config.h"
#include "sysincl.h"
#include "nts_ntp_auth.h"
#include "logging.h"
#include "ntp_ext.h"
#include "nts_ntp.h"
#include "siv.h"
#include "util.h"
struct AuthHeader {
uint16_t nonce_length;
uint16_t ciphertext_length;
};
/* ================================================== */
static int
get_padding_length(int length)
{
return length % 4U ? 4 - length % 4U : 0;
}
/* ================================================== */
static int
get_padded_length(int length)
{
return length + get_padding_length(length);
}
/* ================================================== */
int
NNA_GenerateAuthEF(NTP_Packet *packet, NTP_PacketInfo *info, SIV_Instance siv,
const unsigned char *nonce, int max_nonce_length,
const unsigned char *plaintext, int plaintext_length,
int min_ef_length)
{
int auth_length, ciphertext_length, assoc_length, nonce_length, max_siv_nonce_length;
int nonce_padding, ciphertext_padding, additional_padding;
unsigned char *ciphertext, *body;
struct AuthHeader *header;
assert(sizeof (*header) == 4);
if (max_nonce_length <= 0 || plaintext_length < 0) {
DEBUG_LOG("Invalid nonce/plaintext length");
return 0;
}
assoc_length = info->length;
max_siv_nonce_length = SIV_GetMaxNonceLength(siv);
nonce_length = MIN(max_nonce_length, max_siv_nonce_length);
ciphertext_length = SIV_GetTagLength(siv) + plaintext_length;
nonce_padding = get_padding_length(nonce_length);
ciphertext_padding = get_padding_length(ciphertext_length);
min_ef_length = get_padded_length(min_ef_length);
auth_length = sizeof (*header) + nonce_length + nonce_padding +
ciphertext_length + ciphertext_padding;
additional_padding = MAX(min_ef_length - auth_length - 4, 0);
additional_padding = MAX(MIN(NTS_MIN_UNPADDED_NONCE_LENGTH, max_siv_nonce_length) -
nonce_length - nonce_padding, additional_padding);
auth_length += additional_padding;
if (!NEF_AddBlankField(packet, info, NTP_EF_NTS_AUTH_AND_EEF, auth_length,
(void **)&header)) {
DEBUG_LOG("Could not add EF");
return 0;
}
header->nonce_length = htons(nonce_length);
header->ciphertext_length = htons(ciphertext_length);
body = (unsigned char *)(header + 1);
ciphertext = body + nonce_length + nonce_padding;
BRIEF_ASSERT((unsigned char *)header + auth_length ==
ciphertext + ciphertext_length + ciphertext_padding + additional_padding);
memcpy(body, nonce, nonce_length);
memset(body + nonce_length, 0, nonce_padding);
if (!SIV_Encrypt(siv, nonce, nonce_length, packet, assoc_length,
plaintext, plaintext_length, ciphertext, ciphertext_length)) {
DEBUG_LOG("SIV encrypt failed");
info->length = assoc_length;
info->ext_fields--;
return 0;
}
memset(ciphertext + ciphertext_length, 0, ciphertext_padding + additional_padding);
return 1;
}
/* ================================================== */
int
NNA_DecryptAuthEF(NTP_Packet *packet, NTP_PacketInfo *info, SIV_Instance siv, int ef_start,
unsigned char *plaintext, int buffer_length, int *plaintext_length)
{
int siv_tag_length, max_siv_nonce_length, nonce_length, ciphertext_length;
unsigned char *nonce, *ciphertext;
int ef_type, ef_body_length;
void *ef_body;
struct AuthHeader *header;
if (buffer_length < 0)
return 0;
if (!NEF_ParseField(packet, info->length, ef_start,
NULL, &ef_type, &ef_body, &ef_body_length))
return 0;
if (ef_type != NTP_EF_NTS_AUTH_AND_EEF || ef_body_length < sizeof (*header))
return 0;
header = ef_body;
nonce_length = ntohs(header->nonce_length);
ciphertext_length = ntohs(header->ciphertext_length);
if (get_padded_length(nonce_length) +
get_padded_length(ciphertext_length) > ef_body_length)
return 0;
nonce = (unsigned char *)(header + 1);
ciphertext = nonce + get_padded_length(nonce_length);
max_siv_nonce_length = SIV_GetMaxNonceLength(siv);
siv_tag_length = SIV_GetTagLength(siv);
if (nonce_length < 1 ||
ciphertext_length < siv_tag_length ||
ciphertext_length - siv_tag_length > buffer_length) {
DEBUG_LOG("Unexpected nonce/ciphertext length");
return 0;
}
if (sizeof (*header) + MIN(NTS_MIN_UNPADDED_NONCE_LENGTH, max_siv_nonce_length) +
get_padded_length(ciphertext_length) > ef_body_length) {
DEBUG_LOG("Missing padding");
return 0;
}
*plaintext_length = ciphertext_length - siv_tag_length;
assert(*plaintext_length >= 0);
if (!SIV_Decrypt(siv, nonce, nonce_length, packet, ef_start,
ciphertext, ciphertext_length, plaintext, *plaintext_length)) {
DEBUG_LOG("SIV decrypt failed");
return 0;
}
return 1;
}
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