56 lines
1.2 KiB
C
56 lines
1.2 KiB
C
/* LibTomCrypt, modular cryptographic library -- Tom St Denis */
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/* SPDX-License-Identifier: Unlicense */
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#include "tomcrypt_private.h"
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#ifdef LTC_MDH
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/**
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Check DH public key (INTERNAL ONLY, not part of public API)
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@param key The key you wish to test
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@return CRYPT_OK if successful
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*/
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int dh_check_pubkey(const dh_key *key)
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{
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void *p_minus1;
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ltc_mp_digit digit;
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int i, digit_count, bits_set = 0, err;
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LTC_ARGCHK(key != NULL);
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if ((err = ltc_mp_init(&p_minus1)) != CRYPT_OK) {
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return err;
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}
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/* avoid: y <= 1 OR y >= p-1 */
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if ((err = ltc_mp_sub_d(key->prime, 1, p_minus1)) != CRYPT_OK) {
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goto error;
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}
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if (ltc_mp_cmp(key->y, p_minus1) != LTC_MP_LT || ltc_mp_cmp_d(key->y, 1) != LTC_MP_GT) {
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err = CRYPT_INVALID_ARG;
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goto error;
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}
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/* public key must have more than one bit set */
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digit_count = ltc_mp_get_digit_count(key->y);
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for (i = 0; i < digit_count && bits_set < 2; i++) {
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digit = ltc_mp_get_digit(key->y, i);
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while (digit > 0) {
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if (digit & 1) bits_set++;
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digit >>= 1;
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}
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}
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if (bits_set > 1) {
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err = CRYPT_OK;
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}
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else {
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err = CRYPT_INVALID_ARG;
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}
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error:
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ltc_mp_clear(p_minus1);
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return err;
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}
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#endif /* LTC_MDH */
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