/* SPDX-License-Identifier: GPL-3.0-or-later

 * Copyright © 2019-2025 The TokTok team.

 */

#include "timed_auth.h"

#include <string.h>

#include "attributes.h"

#include "ccompat.h"

#include "crypto_core.h"

#include "mono_time.h"

static void create_timed_auth_to_hash(const Mono_Time *_Nonnull mono_time, uint16_t timeout, bool previous, const uint8_t *_Nullable data,

                                      uint16_t length, uint8_t *_Nonnull to_hash)

{

    const uint64_t t = (mono_time_get(mono_time) / timeout) - (previous ? 1 : 0);

    memcpy(to_hash, &t, sizeof(t));

    if (data != nullptr) {

        memcpy(to_hash + sizeof(t), data, length);

    }

}

void generate_timed_auth(const Mono_Time *mono_time, uint16_t timeout, const uint8_t *key,

                         const uint8_t *data, uint16_t length, uint8_t *timed_auth)

{

    const uint16_t to_hash_size = sizeof(uint64_t) + length;

    VLA(uint8_t, to_hash, to_hash_size);

    create_timed_auth_to_hash(mono_time, timeout, false, data, length, to_hash);

    crypto_hmac(timed_auth, key, to_hash, to_hash_size);

}

bool check_timed_auth(const Mono_Time *mono_time, uint16_t timeout, const uint8_t *key, const uint8_t *data,

                      uint16_t length, const uint8_t *timed_auth)

{

    const uint16_t to_hash_size = sizeof(uint64_t) + length;

    VLA(uint8_t, to_hash, to_hash_size);

    for (uint8_t i = 0; i < 2; ++i) {

        create_timed_auth_to_hash(mono_time, timeout, i != 0, data, length, to_hash);

        if (crypto_hmac_verify(timed_auth, key, to_hash, to_hash_size)) {

            return true;

        }

    }

    return false;

}