EncryptionContext.php

<?php
 
/*
 *
 *  ____            _        _   __  __ _                  __  __ ____
 * |  _ \ ___   ___| | _____| |_|  \/  (_)_ __   ___      |  \/  |  _ \
 * | |_) / _ \ / __| |/ / _ \ __| |\/| | | '_ \ / _ \_____| |\/| | |_) |
 * |  __/ (_) | (__|   <  __/ |_| |  | | | | | |  __/_____| |  | |  __/
 * |_|   \___/ \___|_|\_\___|\__|_|  |_|_|_| |_|\___|     |_|  |_|_|
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * @author PocketMine Team
 * @link http://www.pocketmine.net/
 *
 *
 */
 
declare(strict_types=1);
 
namespace pocketmine\network\mcpe\encryption;
 
use Crypto\Cipher;
use pmmp\encoding\LE;
use function bin2hex;
use function openssl_digest;
use function openssl_error_string;
use function strlen;
use function substr;
 
class EncryptionContext{
    private const CHECKSUM_ALGO = "sha256";
 
    public static bool $ENABLED = true;
 
    private string $key;
 
    private Cipher $decryptCipher;
    private int $decryptCounter = 0;
 
    private Cipher $encryptCipher;
    private int $encryptCounter = 0;
 
    public function __construct(string $encryptionKey, string $algorithm, string $iv){
        $this->key = $encryptionKey;
 
        $this->decryptCipher = new Cipher($algorithm);
        $this->decryptCipher->decryptInit($this->key, $iv);
 
        $this->encryptCipher = new Cipher($algorithm);
        $this->encryptCipher->encryptInit($this->key, $iv);
    }
 
    public static function fakeGCM(string $encryptionKey) : self{
        return new EncryptionContext(
            $encryptionKey,
            "AES-256-CTR",
            substr($encryptionKey, 0, 12) . "\x00\x00\x00\x02"
        );
    }
 
    public static function cfb8(string $encryptionKey) : self{
        return new EncryptionContext(
            $encryptionKey,
            "AES-256-CFB8",
            substr($encryptionKey, 0, 16)
        );
    }
 
    public function decrypt(string $encrypted) : string{
        if(strlen($encrypted) < 9){
            throw new DecryptionException("Payload is too short");
        }
        $decrypted = $this->decryptCipher->decryptUpdate($encrypted);
        $payload = substr($decrypted, 0, -8);
 
        $packetCounter = $this->decryptCounter++;
 
        if(($expected = $this->calculateChecksum($packetCounter, $payload)) !== ($actual = substr($decrypted, -8))){
            throw new DecryptionException("Encrypted packet $packetCounter has invalid checksum (expected " . bin2hex($expected) . ", got " . bin2hex($actual) . ")");
        }
 
        return $payload;
    }
 
    public function encrypt(string $payload) : string{
        return $this->encryptCipher->encryptUpdate($payload . $this->calculateChecksum($this->encryptCounter++, $payload));
    }
 
    private function calculateChecksum(int $counter, string $payload) : string{
        $hash = openssl_digest(LE::packUnsignedLong($counter) . $payload . $this->key, self::CHECKSUM_ALGO, true);
        if($hash === false){
            throw new \RuntimeException("openssl_digest() error: " . openssl_error_string());
        }
        return substr($hash, 0, 8);
    }
}