Шифрование путём обмена ключей

class Encryption
{
    public static function encrypt($key, $data)
    {
        $buf = [];
        $unpackedKey = unpack("H*", $key)[1];
        $buf[] = pack("q", strlen($unpackedKey));
        $buf[] = $unpackedKey;
        $unpackedData = unpack("H*", $data)[1];
        $buf[] = pack("q", strlen($unpackedData));
        $buf[] = $unpackedData;
 
        return implode("", $buf);
    }
 
    public static function decrypt($key, $encrypted)
    {
        $unpackedKeyLength = unpack("q", substr($encrypted, 0, 8))[1];
        $packedKey = pack("H*", substr($encrypted, 8, $unpackedKeyLength));
        if ($packedKey === $key) {
            $unpackedDataLength = unpack("q", substr($encrypted, 8 + $unpackedKeyLength, 8))[1];
            $packedData = pack("H*", substr($encrypted, 8 + $unpackedKeyLength + 8, $unpackedDataLength));
            return $packedData;
        }
 
        return null;
    }
}