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/* Copyright (C) 2018 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
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, see <https://www.gnu.org/licenses/>.
*/
#include <assert.h>
#include <stdint.h>
#include <string.h>
#include "libdnssec/binary.h"
#include "libdnssec/error.h"
#include "libdnssec/key/dnskey.h"
#include "libdnssec/shared/shared.h"
/*!
* Compute keytag for RSA/MD5 key.
*
* \see RFC 2537 (section 2), RFC 4034 (appendix B.1)
*/
static uint16_t keytag_compat(const dnssec_binary_t *rdata)
{
assert(rdata);
assert(rdata->data);
if (rdata->size < 9) { // in fact, the condition could be stricter
return 0;
}
uint8_t msb = rdata->data[rdata->size - 3];
uint8_t lsb = rdata->data[rdata->size - 2];
return (msb << 8) + lsb;
}
/*!
* Compute keytag for other than RSA/MD5 key.
*
* \see RFC 4034 (appendix B)
*/
static uint16_t keytag_current(const dnssec_binary_t *rdata)
{
assert(rdata);
assert(rdata->data);
uint32_t ac = 0;
for (int i = 0; i < rdata->size; i++) {
ac += (i & 1) ? rdata->data[i] : rdata->data[i] << 8;
}
return (ac >> 16) + ac;
}
/* -- public API ----------------------------------------------------------- */
/*!
* Compute keytag for a DNSSEC key.
*/
_public_
int dnssec_keytag(const dnssec_binary_t *rdata, uint16_t *keytag)
{
if (!rdata || !keytag) {
return DNSSEC_EINVAL;
}
if (!rdata->data || rdata->size < DNSKEY_RDATA_OFFSET_PUBKEY) {
return DNSSEC_MALFORMED_DATA;
}
uint8_t algorithm = rdata->data[DNSKEY_RDATA_OFFSET_ALGORITHM];
if (algorithm == 1) {
*keytag = keytag_compat(rdata);
} else {
*keytag = keytag_current(rdata);
}
return DNSSEC_EOK;
}
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