SSH2.php

<?php

/**
 * Pure-PHP implementation of SSHv2.
 *
 * PHP version 5
 *
 * Here are some examples of how to use this library:
 * <code>
 * <?php
 *    include 'vendor/autoload.php';
 *
 *    $ssh = new \phpseclib3\Net\SSH2('www.domain.tld');
 *    if (!$ssh->login('username', 'password')) {
 *        exit('Login Failed');
 *    }
 *
 *    echo $ssh->exec('pwd');
 *    echo $ssh->exec('ls -la');
 * ?>
 * </code>
 *
 * <code>
 * <?php
 *    include 'vendor/autoload.php';
 *
 *    $key = \phpseclib3\Crypt\PublicKeyLoader::load('...', '(optional) password');
 *
 *    $ssh = new \phpseclib3\Net\SSH2('www.domain.tld');
 *    if (!$ssh->login('username', $key)) {
 *        exit('Login Failed');
 *    }
 *
 *    echo $ssh->read('username@username:~$');
 *    $ssh->write("ls -la\n");
 *    echo $ssh->read('username@username:~$');
 * ?>
 * </code>
 *
 * @author    Jim Wigginton <terrafrost@php.net>
 * @copyright 2007 Jim Wigginton
 * @license   http://www.opensource.org/licenses/mit-license.html  MIT License
 * @link      http://phpseclib.sourceforge.net
 */

declare(strict_types=1);

namespace phpseclib3\Net;

use phpseclib3\Common\Functions\Strings;
use phpseclib3\Crypt\Blowfish;
use phpseclib3\Crypt\ChaCha20;
use phpseclib3\Crypt\Common\PrivateKey;
use phpseclib3\Crypt\Common\PublicKey;
use phpseclib3\Crypt\Common\SymmetricKey;
use phpseclib3\Crypt\DH;
use phpseclib3\Crypt\DSA;
use phpseclib3\Crypt\EC;
use phpseclib3\Crypt\Hash;
use phpseclib3\Crypt\Random;
use phpseclib3\Crypt\RC4;
use phpseclib3\Crypt\Rijndael;
use phpseclib3\Crypt\RSA;
use phpseclib3\Crypt\TripleDES;
use phpseclib3\Crypt\Twofish;
use phpseclib3\Exception\ConnectionClosedException;
use phpseclib3\Exception\InsufficientSetupException;
use phpseclib3\Exception\InvalidArgumentException;
use phpseclib3\Exception\LengthException;
use phpseclib3\Exception\LogicException;
use phpseclib3\Exception\NoSupportedAlgorithmsException;
use phpseclib3\Exception\RuntimeException;
use phpseclib3\Exception\UnableToConnectException;
use phpseclib3\Exception\UnexpectedValueException;
use phpseclib3\Exception\UnsupportedAlgorithmException;
use phpseclib3\Exception\UnsupportedCurveException;
use phpseclib3\Math\BigInteger;
use phpseclib3\Net\SSH2\ChannelConnectionFailureReason;
use phpseclib3\Net\SSH2\DisconnectReason;
use phpseclib3\Net\SSH2\MessageType;
use phpseclib3\Net\SSH2\MessageTypeExtra;
use phpseclib3\Net\SSH2\TerminalMode;
use phpseclib3\System\SSH\Agent;

/**
 * Pure-PHP implementation of SSHv2.
 *
 * @author  Jim Wigginton <terrafrost@php.net>
 */
class SSH2
{
    /**#@+
     * Compression Types
     *
     */
    /**
     * No compression
     */
    public const NET_SSH2_COMPRESSION_NONE = 1;
    /**
     * zlib compression
     */
    public const NET_SSH2_COMPRESSION_ZLIB = 2;
    /**
     * zlib@openssh.com
     */
    public const NET_SSH2_COMPRESSION_ZLIB_AT_OPENSSH = 3;
    /**#@-*/

    // Execution Bitmap Masks
    public const MASK_CONSTRUCTOR   = 0x00000001;
    public const MASK_CONNECTED     = 0x00000002;
    public const MASK_LOGIN_REQ     = 0x00000004;
    public const MASK_LOGIN         = 0x00000008;
    public const MASK_SHELL         = 0x00000010;
    public const MASK_WINDOW_ADJUST = 0x00000020;

    /*
     * Channel constants
     *
     * RFC4254 refers not to client and server channels but rather to sender and recipient channels.  we don't refer
     * to them in that way because RFC4254 toggles the meaning. the client sends a SSH_MSG_CHANNEL_OPEN message with
     * a sender channel and the server sends a SSH_MSG_CHANNEL_OPEN_CONFIRMATION in response, with a sender and a
     * recipient channel.  at first glance, you might conclude that SSH_MSG_CHANNEL_OPEN_CONFIRMATION's sender channel
     * would be the same thing as SSH_MSG_CHANNEL_OPEN's sender channel, but it's not, per this snippet:
     *     The 'recipient channel' is the channel number given in the original
     *     open request, and 'sender channel' is the channel number allocated by
     *     the other side.
     *
     * @see \phpseclib3\Net\SSH2::send_channel_packet()
     * @see \phpseclib3\Net\SSH2::get_channel_packet()
     */
    public const CHANNEL_EXEC          = 1; // PuTTy uses 0x100
    public const CHANNEL_SHELL         = 2;
    public const CHANNEL_SUBSYSTEM     = 3;
    public const CHANNEL_AGENT_FORWARD = 4;
    public const CHANNEL_KEEP_ALIVE    = 5;

    /**
     * Returns the message numbers
     *
     * @see \phpseclib3\Net\SSH2::getLog()
     */
    public const LOG_SIMPLE = 1;
    /**
     * Returns the message content
     *
     * @see \phpseclib3\Net\SSH2::getLog()
     */
    public const LOG_COMPLEX = 2;
    /**
     * Outputs the content real-time
     */
    public const LOG_REALTIME = 3;
    /**
     * Dumps the content real-time to a file
     */
    public const LOG_REALTIME_FILE = 4;
    /**
     * Outputs the message numbers real-time
     */
    public const LOG_SIMPLE_REALTIME = 5;
    /**
     * Make sure that the log never gets larger than this
     *
     * @see \phpseclib3\Net\SSH2::getLog()
     */
    public const LOG_MAX_SIZE = 1048576; // 1024 * 1024

    /**
     * Returns when a string matching $expect exactly is found
     *
     * @see \phpseclib3\Net\SSH2::read()
     */
    public const READ_SIMPLE = 1;
    /**
     * Returns when a string matching the regular expression $expect is found
     *
     * @see \phpseclib3\Net\SSH2::read()
     */
    public const READ_REGEX = 2;
    /**
     * Returns whenever a data packet is received.
     *
     * Some data packets may only contain a single character so it may be necessary
     * to call read() multiple times when using this option
     *
     * @see \phpseclib3\Net\SSH2::read()
     */
    public const READ_NEXT = 3;

    /**
     * The SSH identifier
     */
    private string $identifier;

    /**
     * The Socket Object
     *
     * @var resource|closed-resource|null
     */
    public $fsock;

    /**
     * Execution Bitmap
     *
     * The bits that are set represent functions that have been called already.  This is used to determine
     * if a requisite function has been successfully executed.  If not, an error should be thrown.
     */
    protected int $bitmap = 0;

    /**
     * Error information
     *
     * @see self::getErrors()
     * @see self::getLastError()
     */
    private array $errors = [];

    /**
     * Server Identifier
     *
     * @see self::getServerIdentification()
     */
    protected string|false $server_identifier = false;

    /**
     * Key Exchange Algorithms
     *
     * @see self::getKexAlgorithims()
     */
    private array|false $kex_algorithms = false;

    /**
     * Key Exchange Algorithm
     *
     * @see self::getMethodsNegotiated()
     */
    private string|false $kex_algorithm = false;

    /**
     * Minimum Diffie-Hellman Group Bit Size in RFC 4419 Key Exchange Methods
     *
     * @see self::_key_exchange()
     */
    private int $kex_dh_group_size_min = 1536;

    /**
     * Preferred Diffie-Hellman Group Bit Size in RFC 4419 Key Exchange Methods
     *
     * @see self::_key_exchange()
     */
    private int $kex_dh_group_size_preferred = 2048;

    /**
     * Maximum Diffie-Hellman Group Bit Size in RFC 4419 Key Exchange Methods
     *
     * @see self::_key_exchange()
     */
    private int $kex_dh_group_size_max = 4096;

    /**
     * Server Host Key Algorithms
     *
     * @see self::getServerHostKeyAlgorithms()
     */
    private array|false $server_host_key_algorithms = false;

    /**
     * Supported Private Key Algorithms
     *
     * In theory this should be the same as the Server Host Key Algorithms but, in practice,
     * some servers (eg. Azure) will support rsa-sha2-512 as a server host key algorithm but
     * not a private key algorithm
     *
     * @see self::privatekey_login()
     * @var array|false
     */
    private $supported_private_key_algorithms = false;

    /**
     * Encryption Algorithms: Client to Server
     *
     * @see self::getEncryptionAlgorithmsClient2Server()
     */
    private array|false $encryption_algorithms_client_to_server = false;

    /**
     * Encryption Algorithms: Server to Client
     *
     * @see self::getEncryptionAlgorithmsServer2Client()
     */
    private array|false $encryption_algorithms_server_to_client = false;

    /**
     * MAC Algorithms: Client to Server
     *
     * @see self::getMACAlgorithmsClient2Server()
     */
    private array|false $mac_algorithms_client_to_server = false;

    /**
     * MAC Algorithms: Server to Client
     *
     * @see self::getMACAlgorithmsServer2Client()
     */
    private array|false $mac_algorithms_server_to_client = false;

    /**
     * Compression Algorithms: Client to Server
     *
     * @see self::getCompressionAlgorithmsClient2Server()
     */
    private array|false $compression_algorithms_client_to_server = false;

    /**
     * Compression Algorithms: Server to Client
     *
     * @see self::getCompressionAlgorithmsServer2Client()
     */
    private array|false $compression_algorithms_server_to_client = false;

    /**
     * Languages: Server to Client
     */
    private array|false $languages_server_to_client = false;

    /**
     * Languages: Client to Server
     */
    private array|false $languages_client_to_server = false;

    /**
     * Preferred Algorithms
     *
     * @see self::setPreferredAlgorithms()
     */
    private array $preferred = [];

    /**
     * Block Size for Server to Client Encryption
     *
     * "Note that the length of the concatenation of 'packet_length',
     *  'padding_length', 'payload', and 'random padding' MUST be a multiple
     *  of the cipher block size or 8, whichever is larger.  This constraint
     *  MUST be enforced, even when using stream ciphers."
     *
     *  -- http://tools.ietf.org/html/rfc4253#section-6
     *
     * @see self::__construct()
     * @see self::send_binary_packet()
     */
    private int $encrypt_block_size = 8;

    /**
     * Block Size for Client to Server Encryption
     *
     * @see self::__construct()
     * @see self::get_binary_packet()
     */
    private int $decrypt_block_size = 8;

    /**
     * Server to Client Encryption Object
     *
     * @see self::get_binary_packet()
     */
    private SymmetricKey|false $decrypt = false;

    /**
     * Decryption Algorithm Name
     */
    private string|null $decryptName;

    /**
     * Decryption Invocation Counter
     *
     * Used by GCM
     */
    private string|null $decryptInvocationCounter;

    /**
     * Fixed Part of Nonce
     *
     * Used by GCM
     */
    private string|null $decryptFixedPart;

    /**
     * Server to Client Length Encryption Object
     *
     * @see self::get_binary_packet()
     */
    private SymmetricKey|false $lengthDecrypt = false;

    /**
     * Client to Server Encryption Object
     *
     * @see self::send_binary_packet()
     */
    private SymmetricKey|false $encrypt = false;

    /**
     * Encryption Algorithm Name
     */
    private string|null $encryptName;

    /**
     * Encryption Invocation Counter
     *
     * Used by GCM
     */
    private string|null $encryptInvocationCounter;

    /**
     * Fixed Part of Nonce
     *
     * Used by GCM
     */
    private string|null $encryptFixedPart;

    /**
     * Client to Server Length Encryption Object
     *
     * @see self::send_binary_packet()
     */
    private SymmetricKey|false $lengthEncrypt = false;

    /**
     * Client to Server HMAC Object
     *
     * @see self::send_binary_packet()
     */
    private Hash|\stdClass|false $hmac_create = false;

    /**
     * Client to Server HMAC Name
     */
    private string|false $hmac_create_name;

    /**
     * Client to Server ETM
     */
    private int|false $hmac_create_etm;

    /**
     * Server to Client HMAC Object
     *
     * @see self::get_binary_packet()
     */
    private Hash|\stdClass|false $hmac_check = false;

    /**
     * Server to Client HMAC Name
     */
    private string|false $hmac_check_name;

    /**
     * Server to Client ETM
     */
    private int|false $hmac_check_etm;

    /**
     * Size of server to client HMAC
     *
     * We need to know how big the HMAC will be for the server to client direction so that we know how many bytes to read.
     * For the client to server side, the HMAC object will make the HMAC as long as it needs to be.  All we need to do is
     * append it.
     *
     * @see self::get_binary_packet()
     */
    private int|false $hmac_size = false;

    /**
     * Server Public Host Key
     *
     * @see self::getServerPublicHostKey()
     */
    private string $server_public_host_key;

    /**
     * Session identifier
     *
     * "The exchange hash H from the first key exchange is additionally
     *  used as the session identifier, which is a unique identifier for
     *  this connection."
     *
     *  -- http://tools.ietf.org/html/rfc4253#section-7.2
     *
     * @see self::key_exchange()
     */
    private string|false $session_id = false;

    /**
     * Exchange hash
     *
     * The current exchange hash
     *
     * @see self::key_exchange()
     */
    private string|false $exchange_hash = false;

    /**
     * Send Sequence Number
     *
     * See 'Section 6.4.  Data Integrity' of rfc4253 for more info.
     *
     * @see self::send_binary_packet()
     */
    private int $send_seq_no = 0;

    /**
     * Get Sequence Number
     *
     * See 'Section 6.4.  Data Integrity' of rfc4253 for more info.
     *
     * @see self::get_binary_packet()
     */
    private int $get_seq_no = 0;

    /**
     * Server Channels
     *
     * Maps client channels to server channels
     *
     * @see self::get_channel_packet()
     * @see self::exec()
     */
    protected array $server_channels = [];

    /**
     * Channel Buffers
     *
     * If a client requests a packet from one channel but receives two packets from another those packets should
     * be placed in a buffer
     *
     * @see self::get_channel_packet()
     * @see self::exec()
     */
    private array $channel_buffers = [];

    /**
     * Channel Status
     *
     * Contains the type of the last sent message
     *
     * @see self::get_channel_packet()
     */
    protected array $channel_status = [];

    /**
     * The identifier of the interactive channel which was opened most recently
     *
     * @see self::getInteractiveChannelId()
     */
    private int $channel_id_last_interactive = 0;

    /**
     * Packet Size
     *
     * Maximum packet size indexed by channel
     *
     * @see self::send_channel_packet()
     */
    private array $packet_size_client_to_server = [];

    /**
     * Message Number Log
     *
     * @see self::getLog()
     */
    private array $message_number_log = [];

    /**
     * Message Log
     *
     * @see self::getLog()
     */
    private array $message_log = [];

    /**
     * The Window Size
     *
     * Bytes the other party can send before it must wait for the window to be adjusted (0x7FFFFFFF = 2GB)
     *
     * @see self::send_channel_packet()
     * @see self::exec()
     */
    protected int $window_size = 0x7FFFFFFF;

    /**
     * What we resize the window to
     *
     * When PuTTY resizes the window it doesn't add an additional 0x7FFFFFFF bytes - it adds 0x40000000 bytes.
     * Some SFTP clients (GoAnywhere) don't support adding 0x7FFFFFFF to the window size after the fact so
     * we'll just do what PuTTY does
     *
     * @see self::_send_channel_packet()
     * @see self::exec()
     */
    private int $window_resize = 0x40000000;

    /**
     * Window size, server to client
     *
     * Window size indexed by channel
     *
     * @see self::send_channel_packet()
     */
    protected array $window_size_server_to_client = [];

    /**
     * Window size, client to server
     *
     * Window size indexed by channel
     *
     * @see self::get_channel_packet()
     */
    private array $window_size_client_to_server = [];

    /**
     * Server signature
     *
     * Verified against $this->session_id
     *
     * @see self::getServerPublicHostKey()
     */
    private string $signature = '';

    /**
     * Server signature format
     *
     * ssh-rsa or ssh-dss.
     *
     * @see self::getServerPublicHostKey()
     */
    private string $signature_format = '';

    /**
     * Interactive Buffer
     *
     * @see self::read()
     */
    private string $interactiveBuffer = '';

    /**
     * Current log size
     *
     * Should never exceed self::LOG_MAX_SIZE
     *
     * @see self::_send_binary_packet()
     * @see self::_get_binary_packet()
     */
    private int $log_size;

    /**
     * Timeout
     *
     * @see SSH2::setTimeout()
     */
    protected int|null $timeout = null;

    /**
     * Current Timeout
     *
     * @see SSH2::get_channel_packet()
     */
    protected int|float|null $curTimeout = null;

    /**
     * Keep Alive Interval
     *
     * @see self::setKeepAlive()
     */
    private int|null $keepAlive = null;

    /**
     * Real-time log file pointer
     *
     * @see self::_append_log()
     * @var resource|closed-resource
     */
    private $realtime_log_file;

    /**
     * Real-time log file size
     *
     * @see self::_append_log()
     */
    private int $realtime_log_size;

    /**
     * Has the signature been validated?
     *
     * @see self::getServerPublicHostKey()
     */
    private bool $signature_validated = false;

    /**
     * Real-time log file wrap boolean
     *
     * @see self::_append_log()
     */
    private bool $realtime_log_wrap;

    /**
     * Flag to suppress stderr from output
     *
     * @see self::enableQuietMode()
     */
    private bool $quiet_mode = false;

    /**
     * Time of first network activity
     */
    private float $last_packet;

    /**
     * Exit status returned from ssh if any
     */
    private int|null $exit_status = null;

    /**
     * Flag to request a PTY when using exec()
     *
     * @see self::enablePTY()
     */
    private bool $request_pty = false;

    /**
     * Contents of stdError
     */
    private string $stdErrorLog;

    /**
     * The Last Interactive Response
     *
     * @see self::_keyboard_interactive_process()
     */
    private string $last_interactive_response = '';

    /**
     * Keyboard Interactive Request / Responses
     *
     * @see self::_keyboard_interactive_process()
     */
    private array $keyboard_requests_responses = [];

    /**
     * Banner Message
     *
     * Quoting from the RFC, "in some jurisdictions, sending a warning message before
     * authentication may be relevant for getting legal protection."
     *
     * @see self::_filter()
     * @see self::getBannerMessage()
     */
    private string $banner_message = '';

    /**
     * Did read() timeout or return normally?
     *
     * @see self::isTimeout()
     */
    private bool $is_timeout = false;

    /**
     * Log Boundary
     *
     * @see self::_format_log()
     */
    private string $log_boundary = ':';

    /**
     * Log Long Width
     *
     * @see self::_format_log()
     */
    private int $log_long_width = 65;

    /**
     * Log Short Width
     *
     * @see self::_format_log()
     */
    private int $log_short_width = 16;

    /**
     * Hostname
     *
     * @see self::__construct()
     * @see self::_connect()
     */
    private string $host;

    /**
     * Port Number
     *
     * @see self::__construct()
     * @see self::connect()
     */
    private int $port;

    /**
     * Number of columns for terminal window size
     *
     * @see self::getWindowColumns()
     * @see self::setWindowColumns()
     * @see self::setWindowSize()
     */
    private int $windowColumns = 80;

    /**
     * Number of columns for terminal window size
     *
     * @see self::getWindowRows()
     * @see self::setWindowRows()
     * @see self::setWindowSize()
     */
    private int $windowRows = 24;

    /**
     * Crypto Engine
     *
     * @see self::setCryptoEngine()
     * @see self::_key_exchange()
     */
    private static int|false $crypto_engine = false;

    /**
     * A System_SSH_Agent for use in the SSH2 Agent Forwarding scenario
     */
    private Agent $agent;

    /**
     * Connection storage to replicates ssh2 extension functionality:
     * {@link http://php.net/manual/en/wrappers.ssh2.php#refsect1-wrappers.ssh2-examples}
     *
     * @var array<string, \WeakReference<SSH2>>
     */
    private static array $connections;

    /**
     * Send the identification string first?
     */
    private bool $send_id_string_first = true;

    /**
     * Send the key exchange initiation packet first?
     */
    private bool $send_kex_first = true;

    /**
     * Some versions of OpenSSH incorrectly calculate the key size
     */
    private bool $bad_key_size_fix = false;

    /**
     * Should we try to re-connect to re-establish keys?
     */
    private bool $retry_connect = false;

    /**
     * Binary Packet Buffer
     */
    private string|false $binary_packet_buffer = false;

    /**
     * Authentication Credentials
     */
    protected array $auth = [];

    /**
     * Terminal
     */
    private string $term = 'vt100';

    /**
     * The authentication methods that may productively continue authentication.
     *
     * @see https://tools.ietf.org/html/rfc4252#section-5.1
     */
    private array|null $auth_methods_to_continue = null;

    /**
     * Compression method
     */
    private int $compress = self::NET_SSH2_COMPRESSION_NONE;

    /**
     * Decompression method
     */
    private int $decompress = self::NET_SSH2_COMPRESSION_NONE;

    /**
     * Compression context
     *
     * @var resource|false|null
     */
    private $compress_context;

    /**
     * Decompression context
     *
     * @var resource|object
     */
    private $decompress_context;

    /**
     * Regenerate Compression Context
     */
    private bool $regenerate_compression_context = false;

    /**
     * Regenerate Decompression Context
     */
    private bool $regenerate_decompression_context = false;

    /**
     * Smart multi-factor authentication flag
     */
    private bool $smartMFA = true;

    /**
     * How many channels are currently opened
     *
     * @var int
     */
    private $channelCount = 0;

    /**
     * Does the server support multiple channels? If not then error out
     * when multiple channels are attempted to be opened
     *
     * @var bool
     */
    private $errorOnMultipleChannels;

    /**
     * Terrapin Countermeasure
     *
     * "During initial KEX, terminate the connection if any unexpected or out-of-sequence packet is received"
     * -- https://github.com/openssh/openssh-portable/commit/1edb00c58f8a6875fad6a497aa2bacf37f9e6cd5
     *
     * @var int
     */
    private $extra_packets;

    /**
     * Default Constructor.
     *
     * $host can either be a string, representing the host, or a stream resource.
     * If $host is a stream resource then $port doesn't do anything, altho $timeout
     * still will be used
     *
     * @see self::login()
     */
    public function __construct($host, int $port = 22, int $timeout = 10)
    {
        self::$connections[$this->getResourceId()] = \WeakReference::create($this);

        $this->timeout = $timeout;

        if (is_resource($host)) {
            $this->fsock = $host;
            return;
        }

        if (Strings::is_stringable($host)) {
            $this->host = $host;
            $this->port = $port;
        }
    }

    /**
     * Set Crypto Engine Mode
     *
     * Possible $engine values:
     * OpenSSL, Eval, PHP
     */
    public static function setCryptoEngine(int $engine): void
    {
        self::$crypto_engine = $engine;
    }

    /**
     * Send Identification String First
     *
     * https://tools.ietf.org/html/rfc4253#section-4.2 says "when the connection has been established,
     * both sides MUST send an identification string". It does not say which side sends it first. In
     * theory it shouldn't matter but it is a fact of life that some SSH servers are simply buggy
     */
    public function sendIdentificationStringFirst(): void
    {
        $this->send_id_string_first = true;
    }

    /**
     * Send Identification String Last
     *
     * https://tools.ietf.org/html/rfc4253#section-4.2 says "when the connection has been established,
     * both sides MUST send an identification string". It does not say which side sends it first. In
     * theory it shouldn't matter but it is a fact of life that some SSH servers are simply buggy
     */
    public function sendIdentificationStringLast(): void
    {
        $this->send_id_string_first = false;
    }

    /**
     * Send SSH_MSG_KEXINIT First
     *
     * https://tools.ietf.org/html/rfc4253#section-7.1 says "key exchange begins by each sending
     * sending the [SSH_MSG_KEXINIT] packet". It does not say which side sends it first. In theory
     * it shouldn't matter but it is a fact of life that some SSH servers are simply buggy
     */
    public function sendKEXINITFirst(): void
    {
        $this->send_kex_first = true;
    }

    /**
     * Send SSH_MSG_KEXINIT Last
     *
     * https://tools.ietf.org/html/rfc4253#section-7.1 says "key exchange begins by each sending
     * sending the [SSH_MSG_KEXINIT] packet". It does not say which side sends it first. In theory
     * it shouldn't matter but it is a fact of life that some SSH servers are simply buggy
     */
    public function sendKEXINITLast(): void
    {
        $this->send_kex_first = false;
    }

    /**
     * stream_select wrapper
     *
     * Quoting https://stackoverflow.com/a/14262151/569976,
     * "The general approach to `EINTR` is to simply handle the error and retry the operation again"
     *
     * This wrapper does that loop
     */
    private static function stream_select(&$read, &$write, &$except, $seconds, $microseconds = null)
    {
        $remaining = $seconds + $microseconds / 1000000;
        $start = microtime(true);
        while (true) {
            $result = @stream_select($read, $write, $except, $seconds, $microseconds);
            if ($result !== false) {
                return $result;
            }
            $elapsed = microtime(true) - $start;
            $seconds = (int) ($remaining - floor($elapsed));
            $microseconds = (int) (1000000 * ($remaining - $seconds));
            if ($elapsed >= $remaining) {
                return false;
            }
        }
    }

    /**
     * Connect to an SSHv2 server
     *
     * @throws UnexpectedValueException on receipt of unexpected packets
     * @throws RuntimeException on other errors
     */
    private function connect()
    {
        if ($this->bitmap & self::MASK_CONSTRUCTOR) {
            return;
        }

        $this->bitmap |= self::MASK_CONSTRUCTOR;

        $this->curTimeout = $this->timeout;

        $this->last_packet = microtime(true);

        if (!is_resource($this->fsock)) {
            $start = microtime(true);
            // with stream_select a timeout of 0 means that no timeout takes place;
            // with fsockopen a timeout of 0 means that you instantly timeout
            // to resolve this incompatibility a timeout of 100,000 will be used for fsockopen if timeout is 0
            $this->fsock = @fsockopen($this->host, $this->port, $errno, $errstr, $this->curTimeout == 0 ? 100000 : $this->curTimeout);
            if (!$this->fsock) {
                $host = $this->host . ':' . $this->port;
                throw new UnableToConnectException(rtrim("Cannot connect to $host. Error $errno. $errstr"));
            }
            $elapsed = microtime(true) - $start;

            if ($this->curTimeout) {
                $this->curTimeout -= $elapsed;
                if ($this->curTimeout < 0) {
                    throw new RuntimeException('Connection timed out whilst attempting to open socket connection');
                }
            }
        }

        $this->identifier = $this->generate_identifier();

        if ($this->send_id_string_first) {
            fwrite($this->fsock, $this->identifier . "\r\n");
        }

        /* According to the SSH2 specs,

          "The server MAY send other lines of data before sending the version
           string.  Each line SHOULD be terminated by a Carriage Return and Line
           Feed.  Such lines MUST NOT begin with "SSH-", and SHOULD be encoded
           in ISO-10646 UTF-8 [RFC3629] (language is not specified).  Clients
           MUST be able to process such lines." */
        $data = '';
        while (!feof($this->fsock) && !preg_match('#(.*)^(SSH-(\d\.\d+).*)#ms', $data, $matches)) {
            $line = '';
            while (true) {
                if ($this->curTimeout) {
                    if ($this->curTimeout < 0) {
                        throw new RuntimeException('Connection timed out whilst receiving server identification string');
                    }
                    $read = [$this->fsock];
                    $write = $except = null;
                    $start = microtime(true);
                    $sec = (int) floor($this->curTimeout);
                    $usec = (int) (1000000 * ($this->curTimeout - $sec));
                    if (static::stream_select($read, $write, $except, $sec, $usec) === false) {
                        throw new RuntimeException('Connection timed out whilst receiving server identification string');
                    }
                    $elapsed = microtime(true) - $start;
                    $this->curTimeout -= $elapsed;
                }

                $temp = stream_get_line($this->fsock, 255, "\n");
                if ($temp === false) {
                    throw new RuntimeException('Error reading from socket');
                }
                if (strlen($temp) == 255) {
                    continue;
                }

                $line .= "$temp\n";

                // quoting RFC4253, "Implementers who wish to maintain
                // compatibility with older, undocumented versions of this protocol may
                // want to process the identification string without expecting the
                // presence of the carriage return character for reasons described in
                // Section 5 of this document."

                //if (substr($line, -2) == "\r\n") {
                //    break;
                //}

                break;
            }

            $data .= $line;
        }

        if (feof($this->fsock)) {
            $this->bitmap = 0;
            throw new ConnectionClosedException('Connection closed by server');
        }

        $extra = $matches[1];

        if (defined('NET_SSH2_LOGGING')) {
            $this->append_log('<-', $matches[0]);
            $this->append_log('->', $this->identifier . "\r\n");
        }

        $this->server_identifier = trim($temp, "\r\n");
        if (strlen($extra)) {
            $this->errors[] = $data;
        }

        if (version_compare($matches[3], '1.99', '<')) {
            $this->bitmap = 0;
            throw new UnableToConnectException("Cannot connect to SSH $matches[3] servers");
        }

        // Ubuntu's OpenSSH from 5.8 to 6.9 didn't work with multiple channels. see
        // https://bugs.launchpad.net/ubuntu/+source/openssh/+bug/1334916 for more info.
        // https://lists.ubuntu.com/archives/oneiric-changes/2011-July/005772.html discusses
        // when consolekit was incorporated.
        // https://marc.info/?l=openssh-unix-dev&m=163409903417589&w=2 discusses some of the
        // issues with how Ubuntu incorporated consolekit
        $pattern = '#^SSH-2\.0-OpenSSH_([\d.]+)[^ ]* Ubuntu-.*$#';
        $match = preg_match($pattern, $this->server_identifier, $matches);
        $match = $match && version_compare('5.8', $matches[1], '<=');
        $match = $match && version_compare('6.9', $matches[1], '>=');
        $this->errorOnMultipleChannels = $match;

        if (!$this->send_id_string_first) {
            fwrite($this->fsock, $this->identifier . "\r\n");
        }

        if (!$this->send_kex_first) {
            $response = $this->get_binary_packet();

            if (is_bool($response) || !strlen($response) || ord($response[0]) != MessageType::KEXINIT) {
                $this->bitmap = 0;
                throw new UnexpectedValueException('Expected SSH_MSG_KEXINIT');
            }

            $this->key_exchange($response);
        }

        if ($this->send_kex_first) {
            $this->key_exchange();
        }

        $this->bitmap |= self::MASK_CONNECTED;

        return true;
    }

    /**
     * Generates the SSH identifier
     *
     * You should overwrite this method in your own class if you want to use another identifier
     */
    private function generate_identifier(): string
    {
        $identifier = 'SSH-2.0-phpseclib_3.0';

        $ext = [];
        if (extension_loaded('sodium')) {
            $ext[] = 'libsodium';
        }

        if (extension_loaded('openssl')) {
            $ext[] = 'openssl';
        }

        if (extension_loaded('gmp')) {
            $ext[] = 'gmp';
        } elseif (extension_loaded('bcmath')) {
            $ext[] = 'bcmath';
        }

        if (!empty($ext)) {
            $identifier .= ' (' . implode(', ', $ext) . ')';
        }

        return $identifier;
    }

    /**
     * Key Exchange
     *
     * @param string|bool $kexinit_payload_server optional
     * @throws UnexpectedValueException on receipt of unexpected packets
     * @throws RuntimeException on other errors
     * @throws NoSupportedAlgorithmsException when none of the algorithms phpseclib has loaded are compatible
     */
    private function key_exchange($kexinit_payload_server = false): bool
    {
        $preferred = $this->preferred;
        $send_kex = true;

        $kex_algorithms = $preferred['kex'] ??
            SSH2::getSupportedKEXAlgorithms();
        $server_host_key_algorithms = $preferred['hostkey'] ??
            SSH2::getSupportedHostKeyAlgorithms();
        $s2c_encryption_algorithms = $preferred['server_to_client']['crypt'] ??
            SSH2::getSupportedEncryptionAlgorithms();
        $c2s_encryption_algorithms = $preferred['client_to_server']['crypt'] ??
            SSH2::getSupportedEncryptionAlgorithms();
        $s2c_mac_algorithms = $preferred['server_to_client']['mac'] ??
            SSH2::getSupportedMACAlgorithms();
        $c2s_mac_algorithms = $preferred['client_to_server']['mac'] ??
            SSH2::getSupportedMACAlgorithms();
        $s2c_compression_algorithms = $preferred['server_to_client']['comp'] ??
            SSH2::getSupportedCompressionAlgorithms();
        $c2s_compression_algorithms = $preferred['client_to_server']['comp'] ??
            SSH2::getSupportedCompressionAlgorithms();

        $kex_algorithms = array_merge($kex_algorithms, ['ext-info-c', 'kex-strict-c-v00@openssh.com']);

        // some SSH servers have buggy implementations of some of the above algorithms
        switch (true) {
            case $this->server_identifier == 'SSH-2.0-SSHD':
            case substr($this->server_identifier, 0, 13) == 'SSH-2.0-DLINK':
                if (!isset($preferred['server_to_client']['mac'])) {
                    $s2c_mac_algorithms = array_values(array_diff(
                        $s2c_mac_algorithms,
                        ['hmac-sha1-96', 'hmac-md5-96']
                    ));
                }
                if (!isset($preferred['client_to_server']['mac'])) {
                    $c2s_mac_algorithms = array_values(array_diff(
                        $c2s_mac_algorithms,
                        ['hmac-sha1-96', 'hmac-md5-96']
                    ));
                }
                break;
            case substr($this->server_identifier, 0, 24) == 'SSH-2.0-TurboFTP_SERVER_':
                if (!isset($preferred['server_to_client']['crypt'])) {
                    $s2c_encryption_algorithms = array_values(array_diff(
                        $s2c_encryption_algorithms,
                        ['aes128-gcm@openssh.com', 'aes256-gcm@openssh.com']
                    ));
                }
                if (!isset($preferred['client_to_server']['crypt'])) {
                    $c2s_encryption_algorithms = array_values(array_diff(
                        $c2s_encryption_algorithms,
                        ['aes128-gcm@openssh.com', 'aes256-gcm@openssh.com']
                    ));
                }
        }

        $client_cookie = Random::string(16);

        $kexinit_payload_client = pack('Ca*', MessageType::KEXINIT, $client_cookie);
        $kexinit_payload_client .= Strings::packSSH2(
            'L10bN',
            $kex_algorithms,
            $server_host_key_algorithms,
            $c2s_encryption_algorithms,
            $s2c_encryption_algorithms,
            $c2s_mac_algorithms,
            $s2c_mac_algorithms,
            $c2s_compression_algorithms,
            $s2c_compression_algorithms,
            [], // language, client to server
            [], // language, server to client
            false, // first_kex_packet_follows
            0 // reserved for future extension
        );

        if ($kexinit_payload_server === false) {
            $this->send_binary_packet($kexinit_payload_client);

            $this->extra_packets = 0;
            $kexinit_payload_server = $this->get_binary_packet();

            if (
                is_bool($kexinit_payload_server)
                || !strlen($kexinit_payload_server)
                || ord($kexinit_payload_server[0]) != MessageType::KEXINIT
            ) {
                $this->disconnect_helper(DisconnectReason::PROTOCOL_ERROR);
                throw new UnexpectedValueException('Expected SSH_MSG_KEXINIT');
            }

            $send_kex = false;
        }

        $response = $kexinit_payload_server;
        Strings::shift($response, 1); // skip past the message number (it should be SSH_MSG_KEXINIT)
        $server_cookie = Strings::shift($response, 16);

        [
            $this->kex_algorithms,
            $this->server_host_key_algorithms,
            $this->encryption_algorithms_client_to_server,
            $this->encryption_algorithms_server_to_client,
            $this->mac_algorithms_client_to_server,
            $this->mac_algorithms_server_to_client,
            $this->compression_algorithms_client_to_server,
            $this->compression_algorithms_server_to_client,
            $this->languages_client_to_server,
            $this->languages_server_to_client,
            $first_kex_packet_follows
        ] = Strings::unpackSSH2('L10C', $response);
        if (in_array('kex-strict-s-v00@openssh.com', $this->kex_algorithms)) {
            if ($this->session_id === false && $this->extra_packets) {
                throw new \UnexpectedValueException('Possible Terrapin Attack detected');
            }
        }

        $this->supported_private_key_algorithms = $this->server_host_key_algorithms;

        if ($send_kex) {
            $this->send_binary_packet($kexinit_payload_client);
        }

        // we need to decide upon the symmetric encryption algorithms before we do the diffie-hellman key exchange

        // we don't initialize any crypto-objects, yet - we do that, later. for now, we need the lengths to make the
        // diffie-hellman key exchange as fast as possible
        $decrypt = self::array_intersect_first($s2c_encryption_algorithms, $this->encryption_algorithms_server_to_client);
        $decryptKeyLength = $this->encryption_algorithm_to_key_size($decrypt);
        if ($decryptKeyLength === null) {
            $this->disconnect_helper(DisconnectReason::KEY_EXCHANGE_FAILED);
            throw new NoSupportedAlgorithmsException('No compatible server to client encryption algorithms found');
        }

        $encrypt = self::array_intersect_first($c2s_encryption_algorithms, $this->encryption_algorithms_client_to_server);
        $encryptKeyLength = $this->encryption_algorithm_to_key_size($encrypt);
        if ($encryptKeyLength === null) {
            $this->disconnect_helper(DisconnectReason::KEY_EXCHANGE_FAILED);
            throw new NoSupportedAlgorithmsException('No compatible client to server encryption algorithms found');
        }

        // through diffie-hellman key exchange a symmetric key is obtained
        $this->kex_algorithm = self::array_intersect_first($kex_algorithms, $this->kex_algorithms);
        if ($this->kex_algorithm === false) {
            $this->disconnect_helper(DisconnectReason::KEY_EXCHANGE_FAILED);
            throw new NoSupportedAlgorithmsException('No compatible key exchange algorithms found');
        }

        $server_host_key_algorithm = self::array_intersect_first($server_host_key_algorithms, $this->server_host_key_algorithms);
        if ($server_host_key_algorithm === false) {
            $this->disconnect_helper(DisconnectReason::KEY_EXCHANGE_FAILED);
            throw new NoSupportedAlgorithmsException('No compatible server host key algorithms found');
        }

        $mac_algorithm_out = self::array_intersect_first($c2s_mac_algorithms, $this->mac_algorithms_client_to_server);
        if ($mac_algorithm_out === false) {
            $this->disconnect_helper(DisconnectReason::KEY_EXCHANGE_FAILED);
            throw new NoSupportedAlgorithmsException('No compatible client to server message authentication algorithms found');
        }

        $mac_algorithm_in = self::array_intersect_first($s2c_mac_algorithms, $this->mac_algorithms_server_to_client);
        if ($mac_algorithm_in === false) {
            $this->disconnect_helper(DisconnectReason::KEY_EXCHANGE_FAILED);
            throw new NoSupportedAlgorithmsException('No compatible server to client message authentication algorithms found');
        }

        $compression_map = [
            'none' => self::NET_SSH2_COMPRESSION_NONE,
            'zlib' => self::NET_SSH2_COMPRESSION_ZLIB,
            'zlib@openssh.com' => self::NET_SSH2_COMPRESSION_ZLIB_AT_OPENSSH,
        ];

        $compression_algorithm_in = self::array_intersect_first($s2c_compression_algorithms, $this->compression_algorithms_server_to_client);
        if ($compression_algorithm_in === false) {
            $this->disconnect_helper(DisconnectReason::KEY_EXCHANGE_FAILED);
            throw new NoSupportedAlgorithmsException('No compatible server to client compression algorithms found');
        }
        $this->decompress = $compression_map[$compression_algorithm_in];

        $compression_algorithm_out = self::array_intersect_first($c2s_compression_algorithms, $this->compression_algorithms_client_to_server);
        if ($compression_algorithm_out === false) {
            $this->disconnect_helper(DisconnectReason::KEY_EXCHANGE_FAILED);
            throw new NoSupportedAlgorithmsException('No compatible client to server compression algorithms found');
        }
        $this->compress = $compression_map[$compression_algorithm_out];

        switch ($this->kex_algorithm) {
            case 'diffie-hellman-group15-sha512':
            case 'diffie-hellman-group16-sha512':
            case 'diffie-hellman-group17-sha512':
            case 'diffie-hellman-group18-sha512':
            case 'ecdh-sha2-nistp521':
                $kexHash = new Hash('sha512');
                break;
            case 'ecdh-sha2-nistp384':
                $kexHash = new Hash('sha384');
                break;
            case 'diffie-hellman-group-exchange-sha256':
            case 'diffie-hellman-group14-sha256':
            case 'ecdh-sha2-nistp256':
            case 'curve25519-sha256@libssh.org':
            case 'curve25519-sha256':
                $kexHash = new Hash('sha256');
                break;
            default:
                $kexHash = new Hash('sha1');
        }

        // Only relevant in diffie-hellman-group-exchange-sha{1,256}, otherwise empty.

        $exchange_hash_rfc4419 = '';

        if (str_starts_with($this->kex_algorithm, 'curve25519-sha256') || str_starts_with($this->kex_algorithm, 'ecdh-sha2-nistp')) {
            $curve = str_starts_with($this->kex_algorithm, 'curve25519-sha256') ?
                'Curve25519' :
                substr($this->kex_algorithm, 10);
            $ourPrivate = EC::createKey($curve);
            $ourPublicBytes = $ourPrivate->getPublicKey()->getEncodedCoordinates();
            $clientKexInitMessage = MessageTypeExtra::KEX_ECDH_INIT;
            $serverKexReplyMessage = MessageTypeExtra::KEX_ECDH_REPLY;
        } else {
            if (str_starts_with($this->kex_algorithm, 'diffie-hellman-group-exchange')) {
                $dh_group_sizes_packed = pack(
                    'NNN',
                    $this->kex_dh_group_size_min,
                    $this->kex_dh_group_size_preferred,
                    $this->kex_dh_group_size_max
                );
                $packet = pack(
                    'Ca*',
                    MessageTypeExtra::KEXDH_GEX_REQUEST,
                    $dh_group_sizes_packed
                );
                $this->send_binary_packet($packet);
                $this->updateLogHistory('UNKNOWN (34)', 'SSH_MSG_KEXDH_GEX_REQUEST');

                $response = $this->get_binary_packet();

                [$type, $primeBytes, $gBytes] = Strings::unpackSSH2('Css', $response);
                if ($type != MessageTypeExtra::KEXDH_GEX_GROUP) {
                    $this->disconnect_helper(DisconnectReason::PROTOCOL_ERROR);
                    throw new UnexpectedValueException('Expected SSH_MSG_KEX_DH_GEX_GROUP');
                }
                $this->updateLogHistory('UNKNOWN (31)', 'SSH_MSG_KEXDH_GEX_GROUP');
                $prime = new BigInteger($primeBytes, -256);
                $g = new BigInteger($gBytes, -256);

                $exchange_hash_rfc4419 = $dh_group_sizes_packed . Strings::packSSH2(
                    'ss',
                    $primeBytes,
                    $gBytes
                );

                $params = DH::createParameters($prime, $g);
                $clientKexInitMessage = MessageTypeExtra::KEXDH_GEX_INIT;
                $serverKexReplyMessage = MessageTypeExtra::KEXDH_GEX_REPLY;
            } else {
                $params = DH::createParameters($this->kex_algorithm);
                $clientKexInitMessage = MessageType::KEXDH_INIT;
                $serverKexReplyMessage = MessageType::KEXDH_REPLY;
            }

            $keyLength = min($kexHash->getLengthInBytes(), max($encryptKeyLength, $decryptKeyLength));

            $ourPrivate = DH::createKey($params, 16 * $keyLength); // 2 * 8 * $keyLength
            $ourPublic = $ourPrivate->getPublicKey()->toBigInteger();
            $ourPublicBytes = $ourPublic->toBytes(true);
        }

        $data = pack('CNa*', $clientKexInitMessage, strlen($ourPublicBytes), $ourPublicBytes);

        $this->send_binary_packet($data);

        switch ($clientKexInitMessage) {
            case MessageTypeExtra::KEX_ECDH_INIT:
                $this->updateLogHistory('SSH_MSG_KEXDH_INIT', 'SSH_MSG_KEX_ECDH_INIT');
                break;
            case MessageTypeExtra::KEXDH_GEX_INIT:
                $this->updateLogHistory('UNKNOWN (32)', 'SSH_MSG_KEXDH_GEX_INIT');
        }

        $response = $this->get_binary_packet();

        [
            $type,
            $server_public_host_key,
            $theirPublicBytes,
            $this->signature
        ] = Strings::unpackSSH2('Csss', $response);

        if ($type != $serverKexReplyMessage) {
            $this->disconnect_helper(DisconnectReason::PROTOCOL_ERROR);
            throw new UnexpectedValueException("Expected $serverKexReplyMessage");
        }
        switch ($serverKexReplyMessage) {
            case MessageTypeExtra::KEX_ECDH_REPLY:
                $this->updateLogHistory('SSH_MSG_KEXDH_REPLY', 'SSH_MSG_KEX_ECDH_REPLY');
                break;
            case MessageTypeExtra::KEXDH_GEX_REPLY:
                $this->updateLogHistory('UNKNOWN (33)', 'SSH_MSG_KEXDH_GEX_REPLY');
        }

        $this->server_public_host_key = $server_public_host_key;
        [$public_key_format] = Strings::unpackSSH2('s', $server_public_host_key);
        if (strlen($this->signature) < 4) {
            throw new LengthException('The signature needs at least four bytes');
        }
        $temp = unpack('Nlength', substr($this->signature, 0, 4));
        $this->signature_format = substr($this->signature, 4, $temp['length']);

        $keyBytes = DH::computeSecret($ourPrivate, $theirPublicBytes);
        if (($keyBytes & "\xFF\x80") === "\x00\x00") {
            $keyBytes = substr($keyBytes, 1);
        } elseif (($keyBytes[0] & "\x80") === "\x80") {
            $keyBytes = "\0$keyBytes";
        }

        $this->exchange_hash = Strings::packSSH2(
            's5',
            $this->identifier,
            $this->server_identifier,
            $kexinit_payload_client,
            $kexinit_payload_server,
            $this->server_public_host_key
        );
        $this->exchange_hash .= $exchange_hash_rfc4419;
        $this->exchange_hash .= Strings::packSSH2(
            's3',
            $ourPublicBytes,
            $theirPublicBytes,
            $keyBytes
        );

        $this->exchange_hash = $kexHash->hash($this->exchange_hash);

        if ($this->session_id === false) {
            $this->session_id = $this->exchange_hash;
        }

        switch ($server_host_key_algorithm) {
            case 'rsa-sha2-256':
            case 'rsa-sha2-512':
            //case 'ssh-rsa':
                $expected_key_format = 'ssh-rsa';
                break;
            default:
                $expected_key_format = $server_host_key_algorithm;
        }
        if ($public_key_format != $expected_key_format || $this->signature_format != $server_host_key_algorithm) {
            switch (true) {
                case $this->signature_format == $server_host_key_algorithm:
                case $server_host_key_algorithm != 'rsa-sha2-256' && $server_host_key_algorithm != 'rsa-sha2-512':
                case $this->signature_format != 'ssh-rsa':
                    $this->disconnect_helper(DisconnectReason::HOST_KEY_NOT_VERIFIABLE);
                    throw new RuntimeException('Server Host Key Algorithm Mismatch (' . $this->signature_format . ' vs ' . $server_host_key_algorithm . ')');
            }
        }

        $packet = pack('C', MessageType::NEWKEYS);
        $this->send_binary_packet($packet);

        $response = $this->get_binary_packet();

        if ($response === false) {
            $this->disconnect_helper(DisconnectReason::CONNECTION_LOST);
            throw new ConnectionClosedException('Connection closed by server');
        }

        [$type] = Strings::unpackSSH2('C', $response);
        if ($type != MessageType::NEWKEYS) {
            $this->disconnect_helper(DisconnectReason::PROTOCOL_ERROR);
            throw new UnexpectedValueException('Expected SSH_MSG_NEWKEYS');
        }

        if (in_array('kex-strict-s-v00@openssh.com', $this->kex_algorithms)) {
            $this->get_seq_no = $this->send_seq_no = 0;
        }

        $keyBytes = pack('Na*', strlen($keyBytes), $keyBytes);

        $this->encrypt = self::encryption_algorithm_to_crypt_instance($encrypt);
        if ($this->encrypt) {
            if (self::$crypto_engine) {
                $this->encrypt->setPreferredEngine(self::$crypto_engine);
            }
            if ($this->encrypt->getBlockLengthInBytes()) {
                $this->encrypt_block_size = $this->encrypt->getBlockLengthInBytes();
            }
            $this->encrypt->disablePadding();

            if ($this->encrypt->usesIV()) {
                $iv = $kexHash->hash($keyBytes . $this->exchange_hash . 'A' . $this->session_id);
                while ($this->encrypt_block_size > strlen($iv)) {
                    $iv .= $kexHash->hash($keyBytes . $this->exchange_hash . $iv);
                }
                $this->encrypt->setIV(substr($iv, 0, $this->encrypt_block_size));
            }

            switch ($encrypt) {
                case 'aes128-gcm@openssh.com':
                case 'aes256-gcm@openssh.com':
                    $nonce = $kexHash->hash($keyBytes . $this->exchange_hash . 'A' . $this->session_id);
                    $this->encryptFixedPart = substr($nonce, 0, 4);
                    $this->encryptInvocationCounter = substr($nonce, 4, 8);
                    // fall-through
                case 'chacha20-poly1305@openssh.com':
                    break;
                default:
                    $this->encrypt->enableContinuousBuffer();
            }

            $key = $kexHash->hash($keyBytes . $this->exchange_hash . 'C' . $this->session_id);
            while ($encryptKeyLength > strlen($key)) {
                $key .= $kexHash->hash($keyBytes . $this->exchange_hash . $key);
            }
            switch ($encrypt) {
                case 'chacha20-poly1305@openssh.com':
                    $encryptKeyLength = 32;
                    $this->lengthEncrypt = self::encryption_algorithm_to_crypt_instance($encrypt);
                    $this->lengthEncrypt->setKey(substr($key, 32, 32));
            }
            $this->encrypt->setKey(substr($key, 0, $encryptKeyLength));
            $this->encryptName = $encrypt;
        }

        $this->decrypt = self::encryption_algorithm_to_crypt_instance($decrypt);
        if ($this->decrypt) {
            if (self::$crypto_engine) {
                $this->decrypt->setPreferredEngine(self::$crypto_engine);
            }
            if ($this->decrypt->getBlockLengthInBytes()) {
                $this->decrypt_block_size = $this->decrypt->getBlockLengthInBytes();
            }
            $this->decrypt->disablePadding();

            if ($this->decrypt->usesIV()) {
                $iv = $kexHash->hash($keyBytes . $this->exchange_hash . 'B' . $this->session_id);
                while ($this->decrypt_block_size > strlen($iv)) {
                    $iv .= $kexHash->hash($keyBytes . $this->exchange_hash . $iv);
                }
                $this->decrypt->setIV(substr($iv, 0, $this->decrypt_block_size));
            }

            switch ($decrypt) {
                case 'aes128-gcm@openssh.com':
                case 'aes256-gcm@openssh.com':
                    // see https://tools.ietf.org/html/rfc5647#section-7.1
                    $nonce = $kexHash->hash($keyBytes . $this->exchange_hash . 'B' . $this->session_id);
                    $this->decryptFixedPart = substr($nonce, 0, 4);
                    $this->decryptInvocationCounter = substr($nonce, 4, 8);
                    // fall-through
                case 'chacha20-poly1305@openssh.com':
                    break;
                default:
                    $this->decrypt->enableContinuousBuffer();
            }

            $key = $kexHash->hash($keyBytes . $this->exchange_hash . 'D' . $this->session_id);
            while ($decryptKeyLength > strlen($key)) {
                $key .= $kexHash->hash($keyBytes . $this->exchange_hash . $key);
            }
            switch ($decrypt) {
                case 'chacha20-poly1305@openssh.com':
                    $decryptKeyLength = 32;
                    $this->lengthDecrypt = self::encryption_algorithm_to_crypt_instance($decrypt);
                    $this->lengthDecrypt->setKey(substr($key, 32, 32));
            }
            $this->decrypt->setKey(substr($key, 0, $decryptKeyLength));
            $this->decryptName = $decrypt;
        }

        /* The "arcfour128" algorithm is the RC4 cipher, as described in
           [SCHNEIER], using a 128-bit key.  The first 1536 bytes of keystream
           generated by the cipher MUST be discarded, and the first byte of the
           first encrypted packet MUST be encrypted using the 1537th byte of
           keystream.

           -- http://tools.ietf.org/html/rfc4345#section-4 */
        if ($encrypt == 'arcfour128' || $encrypt == 'arcfour256') {
            $this->encrypt->encrypt(str_repeat("\0", 1536));
        }
        if ($decrypt == 'arcfour128' || $decrypt == 'arcfour256') {
            $this->decrypt->decrypt(str_repeat("\0", 1536));
        }

        if (!$this->encrypt->usesNonce()) {
            [$this->hmac_create, $createKeyLength] = self::mac_algorithm_to_hash_instance($mac_algorithm_out);
        } else {
            $this->hmac_create = new \stdClass();
            $this->hmac_create_name = $mac_algorithm_out;
            //$mac_algorithm_out = 'none';
            $createKeyLength = 0;
        }

        if ($this->hmac_create instanceof Hash) {
            $key = $kexHash->hash($keyBytes . $this->exchange_hash . 'E' . $this->session_id);
            while ($createKeyLength > strlen($key)) {
                $key .= $kexHash->hash($keyBytes . $this->exchange_hash . $key);
            }
            $this->hmac_create->setKey(substr($key, 0, $createKeyLength));
            $this->hmac_create_name = $mac_algorithm_out;
            $this->hmac_create_etm = preg_match('#-etm@openssh\.com$#', $mac_algorithm_out);
        }

        if (!$this->decrypt->usesNonce()) {
            [$this->hmac_check, $checkKeyLength] = self::mac_algorithm_to_hash_instance($mac_algorithm_in);
            $this->hmac_size = $this->hmac_check->getLengthInBytes();
        } else {
            $this->hmac_check = new \stdClass();
            $this->hmac_check_name = $mac_algorithm_in;
            //$mac_algorithm_in = 'none';
            $checkKeyLength = 0;
            $this->hmac_size = 0;
        }

        if ($this->hmac_check instanceof Hash) {
            $key = $kexHash->hash($keyBytes . $this->exchange_hash . 'F' . $this->session_id);
            while ($checkKeyLength > strlen($key)) {
                $key .= $kexHash->hash($keyBytes . $this->exchange_hash . $key);
            }
            $this->hmac_check->setKey(substr($key, 0, $checkKeyLength));
            $this->hmac_check_name = $mac_algorithm_in;
            $this->hmac_check_etm = preg_match('#-etm@openssh\.com$#', $mac_algorithm_in);
        }

        $this->regenerate_compression_context = $this->regenerate_decompression_context = true;

        return true;
    }

    /**
     * Maps an encryption algorithm name to the number of key bytes.
     *
     * @param string $algorithm Name of the encryption algorithm
     * @return int|null Number of bytes as an integer or null for unknown
     */
    private function encryption_algorithm_to_key_size(string $algorithm): ?int
    {
        if ($this->bad_key_size_fix && self::bad_algorithm_candidate($algorithm)) {
            return 16;
        }

        switch ($algorithm) {
            case 'none':
                return 0;
            case 'aes128-gcm@openssh.com':
            case 'aes128-cbc':
            case 'aes128-ctr':
            case 'arcfour':
            case 'arcfour128':
            case 'blowfish-cbc':
            case 'blowfish-ctr':
            case 'twofish128-cbc':
            case 'twofish128-ctr':
                return 16;
            case '3des-cbc':
            case '3des-ctr':
            case 'aes192-cbc':
            case 'aes192-ctr':
            case 'twofish192-cbc':
            case 'twofish192-ctr':
                return 24;
            case 'aes256-gcm@openssh.com':
            case 'aes256-cbc':
            case 'aes256-ctr':
            case 'arcfour256':
            case 'twofish-cbc':
            case 'twofish256-cbc':
            case 'twofish256-ctr':
                return 32;
            case 'chacha20-poly1305@openssh.com':
                return 64;
        }
        return null;
    }

    /**
     * Maps an encryption algorithm name to an instance of a subclass of
     * \phpseclib3\Crypt\Common\SymmetricKey.
     *
     * @param string $algorithm Name of the encryption algorithm
     * @return SymmetricKey|null
     */
    private static function encryption_algorithm_to_crypt_instance(string $algorithm)
    {
        switch ($algorithm) {
            case '3des-cbc':
                return new TripleDES('cbc');
            case '3des-ctr':
                return new TripleDES('ctr');
            case 'aes256-cbc':
            case 'aes192-cbc':
            case 'aes128-cbc':
                return new Rijndael('cbc');
            case 'aes256-ctr':
            case 'aes192-ctr':
            case 'aes128-ctr':
                return new Rijndael('ctr');
            case 'blowfish-cbc':
                return new Blowfish('cbc');
            case 'blowfish-ctr':
                return new Blowfish('ctr');
            case 'twofish128-cbc':
            case 'twofish192-cbc':
            case 'twofish256-cbc':
            case 'twofish-cbc':
                return new Twofish('cbc');
            case 'twofish128-ctr':
            case 'twofish192-ctr':
            case 'twofish256-ctr':
                return new Twofish('ctr');
            case 'arcfour':
            case 'arcfour128':
            case 'arcfour256':
                return new RC4();
            case 'aes128-gcm@openssh.com':
            case 'aes256-gcm@openssh.com':
                return new Rijndael('gcm');
            case 'chacha20-poly1305@openssh.com':
                return new ChaCha20();
        }
        return null;
    }

    /**
     * Maps an encryption algorithm name to an instance of a subclass of
     * \phpseclib3\Crypt\Hash.
     *
     * @param string $algorithm Name of the encryption algorithm
     * @return array{Hash, int}|null
     */
    private static function mac_algorithm_to_hash_instance(string $algorithm): ?array
    {
        switch ($algorithm) {
            case 'umac-64@openssh.com':
            case 'umac-64-etm@openssh.com':
                return [new Hash('umac-64'), 16];
            case 'umac-128@openssh.com':
            case 'umac-128-etm@openssh.com':
                return [new Hash('umac-128'), 16];
            case 'hmac-sha2-512':
            case 'hmac-sha2-512-etm@openssh.com':
                return [new Hash('sha512'), 64];
            case 'hmac-sha2-256':
            case 'hmac-sha2-256-etm@openssh.com':
                return [new Hash('sha256'), 32];
            case 'hmac-sha1':
            case 'hmac-sha1-etm@openssh.com':
                return [new Hash('sha1'), 20];
            case 'hmac-sha1-96':
                return [new Hash('sha1-96'), 20];
            case 'hmac-md5':
                return [new Hash('md5'), 16];
            case 'hmac-md5-96':
                return [new Hash('md5-96'), 16];
        }
    }

    /*
     * Tests whether or not proposed algorithm has a potential for issues
     *
     * @link https://www.chiark.greenend.org.uk/~sgtatham/putty/wishlist/ssh2-aesctr-openssh.html
     * @link https://bugzilla.mindrot.org/show_bug.cgi?id=1291
     * @param string $algorithm Name of the encryption algorithm
     * @return bool
     */
    private static function bad_algorithm_candidate($algorithm): bool
    {
        switch ($algorithm) {
            case 'arcfour256':
            case 'aes192-ctr':
            case 'aes256-ctr':
                return true;
        }

        return false;
    }

    /**
     * Login
     *
     * The $password parameter can be a plaintext password, a \phpseclib3\Crypt\RSA|EC|DSA object, a \phpseclib3\System\SSH\Agent object or an array
     *
     * @param string|PrivateKey|array[]|Agent|null ...$args
     * @see self::_login()
     */
    public function login(string $username, ...$args): bool
    {
        if (!$this->retry_connect) {
            $this->auth[] = func_get_args();
        }

        // try logging with 'none' as an authentication method first since that's what
        // PuTTY does
        if (
            substr($this->server_identifier ?: '', 0, 15) !== 'SSH-2.0-CoreFTP' &&
            $this->auth_methods_to_continue === null
        ) {
            if ($this->sublogin($username)) {
                return true;
            }
            if (!count($args)) {
                return false;
            }
        }
        return $this->sublogin($username, ...$args);
    }

    /**
     * Login Helper
     *
     * @param string|PrivateKey|array[]|Agent|null ...$args
     * @see self::_login_helper()
     */
    protected function sublogin(string $username, ...$args): bool
    {
        if (!($this->bitmap & self::MASK_CONSTRUCTOR)) {
            $this->connect();
        }

        if (empty($args)) {
            return $this->login_helper($username);
        }

        foreach ($args as $arg) {
            switch (true) {
                case $arg instanceof PublicKey:
                    throw new UnexpectedValueException('A PublicKey object was passed to the login method instead of a PrivateKey object');
                case $arg instanceof PrivateKey:
                case $arg instanceof Agent:
                case is_array($arg):
                case Strings::is_stringable($arg):
                    break;
                default:
                    throw new UnexpectedValueException('$password needs to either be an instance of \phpseclib3\Crypt\Common\PrivateKey, \System\SSH\Agent, an array or a string');
            }
        }

        while (count($args)) {
            if (!$this->auth_methods_to_continue || !$this->smartMFA) {
                $newargs = $args;
                $args = [];
            } else {
                $newargs = [];
                foreach ($this->auth_methods_to_continue as $method) {
                    switch ($method) {
                        case 'publickey':
                            foreach ($args as $key => $arg) {
                                if ($arg instanceof PrivateKey || $arg instanceof Agent) {
                                    $newargs[] = $arg;
                                    unset($args[$key]);
                                    break;
                                }
                            }
                            break;
                        case 'keyboard-interactive':
                            $hasArray = $hasString = false;
                            foreach ($args as $arg) {
                                if ($hasArray || is_array($arg)) {
                                    $hasArray = true;
                                    break;
                                }
                                if ($hasString || Strings::is_stringable($arg)) {
                                    $hasString = true;
                                    break;
                                }
                            }
                            if ($hasArray && $hasString) {
                                foreach ($args as $key => $arg) {
                                    if (is_array($arg)) {
                                        $newargs[] = $arg;
                                        break 2;
                                    }
                                }
                            }
                            // fall-through
                        case 'password':
                            foreach ($args as $key => $arg) {
                                $newargs[] = $arg;
                                unset($args[$key]);
                                break;
                            }
                    }
                }
            }

            if (!count($newargs)) {
                return false;
            }

            foreach ($newargs as $arg) {
                if ($this->login_helper($username, $arg)) {
                    return true;
                }
            }
        }
        return false;
    }

    /**
     * Login Helper
     *
     * {@internal It might be worthwhile, at some point, to protect against {@link http://tools.ietf.org/html/rfc4251#section-9.3.9 traffic analysis}
     *           by sending dummy SSH_MSG_IGNORE messages.}
     *
     * @throws UnexpectedValueException on receipt of unexpected packets
     * @throws RuntimeException on other errors
     */
    private function login_helper(string $username, $password = null): bool
    {
        if (!($this->bitmap & self::MASK_CONNECTED)) {
            return false;
        }

        if (!($this->bitmap & self::MASK_LOGIN_REQ)) {
            $packet = Strings::packSSH2('Cs', MessageType::SERVICE_REQUEST, 'ssh-userauth');
            $this->send_binary_packet($packet);

            try {
                $response = $this->get_binary_packet();
            } catch (\Exception $e) {
                if ($this->retry_connect) {
                    $this->retry_connect = false;
                    $this->connect();
                    return $this->login_helper($username, $password);
                }
                $this->disconnect_helper(DisconnectReason::CONNECTION_LOST);
                throw $e;
            }

            [$type] = Strings::unpackSSH2('C', $response);

            if ($type == MessageType::EXT_INFO) {
                [$nr_extensions] = Strings::unpackSSH2('N', $response);
                for ($i = 0; $i < $nr_extensions; $i++) {
                    [$extension_name, $extension_value] = Strings::unpackSSH2('ss', $response);
                    if ($extension_name == 'server-sig-algs') {
                        $this->supported_private_key_algorithms = explode(',', $extension_value);
                    }
                }

                $response = $this->get_binary_packet();
                [$type] = Strings::unpackSSH2('C', $response);
            }

            [$service] = Strings::unpackSSH2('s', $response);
            if ($type != MessageType::SERVICE_ACCEPT || $service != 'ssh-userauth') {
                $this->disconnect_helper(DisconnectReason::PROTOCOL_ERROR);
                throw new UnexpectedValueException('Expected SSH_MSG_SERVICE_ACCEPT');
            }
            $this->bitmap |= self::MASK_LOGIN_REQ;
        }

        if (strlen($this->last_interactive_response)) {
            return !Strings::is_stringable($password) && !is_array($password) ? false : $this->keyboard_interactive_process($password);
        }

        if ($password instanceof PrivateKey) {
            return $this->privatekey_login($username, $password);
        }

        if ($password instanceof Agent) {
            return $this->ssh_agent_login($username, $password);
        }

        if (is_array($password)) {
            if ($this->keyboard_interactive_login($username, $password)) {
                $this->bitmap |= self::MASK_LOGIN;
                return true;
            }
            return false;
        }

        if (!isset($password)) {
            $packet = Strings::packSSH2(
                'Cs3',
                MessageType::USERAUTH_REQUEST,
                $username,
                'ssh-connection',
                'none'
            );

            $this->send_binary_packet($packet);

            $response = $this->get_binary_packet();

            [$type] = Strings::unpackSSH2('C', $response);
            switch ($type) {
                case MessageType::USERAUTH_SUCCESS:
                    $this->bitmap |= self::MASK_LOGIN;
                    return true;
                case MessageType::USERAUTH_FAILURE:
                    [$auth_methods] = Strings::unpackSSH2('L', $response);
                    $this->auth_methods_to_continue = $auth_methods;
                    // fall-through
                default:
                    return false;
            }
        }

        $packet = Strings::packSSH2(
            'Cs3bs',
            MessageType::USERAUTH_REQUEST,
            $username,
            'ssh-connection',
            'password',
            false,
            $password
        );

        // remove the username and password from the logged packet
        if (!defined('NET_SSH2_LOGGING')) {
            $logged = null;
        } else {
            $logged = Strings::packSSH2(
                'Cs3bs',
                MessageType::USERAUTH_REQUEST,
                $username,
                'ssh-connection',
                'password',
                false,
                'password'
            );
        }

        $this->send_binary_packet($packet, $logged);

        $response = $this->get_binary_packet();
        if ($response === false) {
            return false;
        }
        [$type] = Strings::unpackSSH2('C', $response);
        switch ($type) {
            case MessageTypeExtra::USERAUTH_PASSWD_CHANGEREQ: // in theory, the password can be changed
                $this->updateLogHistory('SSH_MSG_USERAUTH_INFO_REQUEST', 'SSH_MSG_USERAUTH_PASSWD_CHANGEREQ');

                [$message] = Strings::unpackSSH2('s', $response);
                $this->errors[] = 'SSH_MSG_USERAUTH_PASSWD_CHANGEREQ: ' . $message;

                return $this->disconnect_helper(DisconnectReason::AUTH_CANCELLED_BY_USER);
            case MessageType::USERAUTH_FAILURE:
                // can we use keyboard-interactive authentication?  if not then either the login is bad or the server employees
                // multi-factor authentication
                [$auth_methods, $partial_success] = Strings::unpackSSH2('Lb', $response);
                $this->auth_methods_to_continue = $auth_methods;
                if (!$partial_success && in_array('keyboard-interactive', $auth_methods)) {
                    if ($this->keyboard_interactive_login($username, $password)) {
                        $this->bitmap |= self::MASK_LOGIN;
                        return true;
                    }
                    return false;
                }
                return false;
            case MessageType::USERAUTH_SUCCESS:
                $this->bitmap |= self::MASK_LOGIN;
                return true;
        }

        return false;
    }

    /**
     * Login via keyboard-interactive authentication
     *
     * See {@link http://tools.ietf.org/html/rfc4256 RFC4256} for details.  This is not a full-featured keyboard-interactive authenticator.
     *
     * @param string|array $password
     */
    private function keyboard_interactive_login(string $username, $password): bool
    {
        $packet = Strings::packSSH2(
            'Cs5',
            MessageType::USERAUTH_REQUEST,
            $username,
            'ssh-connection',
            'keyboard-interactive',
            '', // language tag
            '' // submethods
        );
        $this->send_binary_packet($packet);

        return $this->keyboard_interactive_process($password);
    }

    /**
     * Handle the keyboard-interactive requests / responses.
     *
     * @throws RuntimeException on connection error
     */
    private function keyboard_interactive_process(...$responses)
    {
        if (strlen($this->last_interactive_response)) {
            $response = $this->last_interactive_response;
        } else {
            $orig = $response = $this->get_binary_packet();
        }

        [$type] = Strings::unpackSSH2('C', $response);
        switch ($type) {
            case MessageType::USERAUTH_INFO_REQUEST:
                [
                    , // name; may be empty
                    , // instruction; may be empty
                    , // language tag; may be empty
                    $num_prompts
                ] = Strings::unpackSSH2('s3N', $response);

                for ($i = 0; $i < count($responses); $i++) {
                    if (is_array($responses[$i])) {
                        foreach ($responses[$i] as $key => $value) {
                            $this->keyboard_requests_responses[$key] = $value;
                        }
                        unset($responses[$i]);
                    }
                }
                $responses = array_values($responses);

                if (isset($this->keyboard_requests_responses)) {
                    for ($i = 0; $i < $num_prompts; $i++) {
                        [
                            $prompt, // prompt - ie. "Password: "; must not be empty
                            // echo
                        ] = Strings::unpackSSH2('sC', $response);
                        foreach ($this->keyboard_requests_responses as $key => $value) {
                            if (substr($prompt, 0, strlen($key)) == $key) {
                                $responses[] = $value;
                                break;
                            }
                        }
                    }
                }

                // see http://tools.ietf.org/html/rfc4256#section-3.2
                if (strlen($this->last_interactive_response)) {
                    $this->last_interactive_response = '';
                } else {
                    $this->updateLogHistory('UNKNOWN (60)', 'SSH_MSG_USERAUTH_INFO_REQUEST');
                }

                if (!count($responses) && $num_prompts) {
                    $this->last_interactive_response = $orig;
                    return false;
                }

                /*
                   After obtaining the requested information from the user, the client
                   MUST respond with an SSH_MSG_USERAUTH_INFO_RESPONSE message.
                */
                // see http://tools.ietf.org/html/rfc4256#section-3.4
                $packet = $logged = pack('CN', MessageType::USERAUTH_INFO_RESPONSE, count($responses));
                for ($i = 0; $i < count($responses); $i++) {
                    $packet .= Strings::packSSH2('s', $responses[$i]);
                    $logged .= Strings::packSSH2('s', 'dummy-answer');
                }

                $this->send_binary_packet($packet, $logged);

                $this->updateLogHistory('UNKNOWN (61)', 'SSH_MSG_USERAUTH_INFO_RESPONSE');

                /*
                   After receiving the response, the server MUST send either an
                   SSH_MSG_USERAUTH_SUCCESS, SSH_MSG_USERAUTH_FAILURE, or another
                   SSH_MSG_USERAUTH_INFO_REQUEST message.
                */
                // maybe phpseclib should force close the connection after x request / responses?  unless something like that is done
                // there could be an infinite loop of request / responses.
                return $this->keyboard_interactive_process();
            case MessageType::USERAUTH_SUCCESS:
                return true;
            case MessageType::USERAUTH_FAILURE:
                [$auth_methods] = Strings::unpackSSH2('L', $response);
                $this->auth_methods_to_continue = $auth_methods;
                return false;
        }

        return false;
    }

    /**
     * Login with an ssh-agent provided key
     */
    private function ssh_agent_login(string $username, Agent $agent): bool
    {
        $this->agent = $agent;
        $keys = $agent->requestIdentities();
        foreach ($keys as $key) {
            if ($this->privatekey_login($username, $key)) {
                return true;
            }
        }

        return false;
    }

    /**
     * Login with an RSA private key
     *
     * {@internal It might be worthwhile, at some point, to protect against {@link http://tools.ietf.org/html/rfc4251#section-9.3.9 traffic analysis}
     *           by sending dummy SSH_MSG_IGNORE messages.}
     *
     * @throws RuntimeException on connection error
     */
    private function privatekey_login(string $username, PrivateKey $privatekey): bool
    {
        $publickey = $privatekey->getPublicKey();

        if ($publickey instanceof RSA) {
            $privatekey = $privatekey->withPadding(RSA::SIGNATURE_PKCS1);
            $algos = ['rsa-sha2-256', 'rsa-sha2-512', 'ssh-rsa'];
            if (isset($this->preferred['hostkey'])) {
                $algos = array_intersect($algos, $this->preferred['hostkey']);
            }
            $algo = self::array_intersect_first($algos, $this->supported_private_key_algorithms);
            switch ($algo) {
                case 'rsa-sha2-512':
                    $hash = 'sha512';
                    $signatureType = 'rsa-sha2-512';
                    break;
                case 'rsa-sha2-256':
                    $hash = 'sha256';
                    $signatureType = 'rsa-sha2-256';
                    break;
                //case 'ssh-rsa':
                default:
                    $hash = 'sha1';
                    $signatureType = 'ssh-rsa';
            }
        } elseif ($publickey instanceof EC) {
            $privatekey = $privatekey->withSignatureFormat('SSH2');
            $curveName = $privatekey->getCurve();
            switch ($curveName) {
                case 'Ed25519':
                    $hash = 'sha512';
                    $signatureType = 'ssh-ed25519';
                    break;
                case 'secp256r1': // nistp256
                    $hash = 'sha256';
                    $signatureType = 'ecdsa-sha2-nistp256';
                    break;
                case 'secp384r1': // nistp384
                    $hash = 'sha384';
                    $signatureType = 'ecdsa-sha2-nistp384';
                    break;
                case 'secp521r1': // nistp521
                    $hash = 'sha512';
                    $signatureType = 'ecdsa-sha2-nistp521';
                    break;
                default:
                    if (is_array($curveName)) {
                        throw new UnsupportedCurveException('Specified Curves are not supported by SSH2');
                    }
                    throw new UnsupportedCurveException('Named Curve of ' . $curveName . ' is not supported by phpseclib3\'s SSH2 implementation');
            }
        } elseif ($publickey instanceof DSA) {
            $privatekey = $privatekey->withSignatureFormat('SSH2');
            $hash = 'sha1';
            $signatureType = 'ssh-dss';
        } else {
            throw new UnsupportedAlgorithmException('Please use either an RSA key, an EC one or a DSA key');
        }

        $publickeyStr = $publickey->toString('OpenSSH', ['binary' => true]);

        $part1 = Strings::packSSH2(
            'Csss',
            MessageType::USERAUTH_REQUEST,
            $username,
            'ssh-connection',
            'publickey'
        );
        $part2 = Strings::packSSH2('ss', $signatureType, $publickeyStr);

        $packet = $part1 . chr(0) . $part2;
        $this->send_binary_packet($packet);

        $response = $this->get_binary_packet();

        [$type] = Strings::unpackSSH2('C', $response);
        switch ($type) {
            case MessageType::USERAUTH_FAILURE:
                [$auth_methods] = Strings::unpackSSH2('L', $response);
                if (in_array('publickey', $auth_methods) && substr($signatureType, 0, 9) == 'rsa-sha2-') {
                    $this->supported_private_key_algorithms = array_diff($this->supported_private_key_algorithms, ['rsa-sha2-256', 'rsa-sha2-512']);
                    return $this->privatekey_login($username, $privatekey);
                }
                $this->auth_methods_to_continue = $auth_methods;
                $this->errors[] = 'SSH_MSG_USERAUTH_FAILURE';
                return false;
            case MessageTypeExtra::USERAUTH_PK_OK:
                // we'll just take it on faith that the public key blob and the public key algorithm name are as
                // they should be
                $this->updateLogHistory('SSH_MSG_USERAUTH_INFO_REQUEST', 'SSH_MSG_USERAUTH_PK_OK');
                break;
            case MessageType::USERAUTH_SUCCESS:
                $this->bitmap |= self::MASK_LOGIN;
                return true;
            default:
                $this->disconnect_helper(DisconnectReason::BY_APPLICATION);
                throw new ConnectionClosedException('Unexpected response to publickey authentication pt 1');
        }

        $packet = $part1 . chr(1) . $part2;
        $privatekey = $privatekey->withHash($hash);
        $signature = $privatekey->sign(Strings::packSSH2('s', $this->session_id) . $packet);
        if ($publickey instanceof RSA) {
            $signature = Strings::packSSH2('ss', $signatureType, $signature);
        }
        $packet .= Strings::packSSH2('s', $signature);

        $this->send_binary_packet($packet);

        $response = $this->get_binary_packet();

        [$type] = Strings::unpackSSH2('C', $response);
        switch ($type) {
            case MessageType::USERAUTH_FAILURE:
                // either the login is bad or the server employs multi-factor authentication
                [$auth_methods] = Strings::unpackSSH2('L', $response);
                $this->auth_methods_to_continue = $auth_methods;
                return false;
            case MessageType::USERAUTH_SUCCESS:
                $this->bitmap |= self::MASK_LOGIN;
                return true;
        }

        $this->disconnect_helper(DisconnectReason::BY_APPLICATION);
        throw new ConnectionClosedException('Unexpected response to publickey authentication pt 2');
    }

    /**
     * Return the currently configured timeout
     */
    public function getTimeout(): int
    {
        return $this->timeout;
    }

    /**
     * Set Timeout
     *
     * $ssh->exec('ping 127.0.0.1'); on a Linux host will never return and will run indefinitely.  setTimeout() makes it so it'll timeout.
     * Setting $timeout to false or 0 will mean there is no timeout.
     */
    public function setTimeout(int $timeout): void
    {
        $this->timeout = $this->curTimeout = $timeout;
    }

    /**
     * Set Keep Alive
     *
     * Sends an SSH2_MSG_IGNORE message every x seconds, if x is a positive non-zero number.
     */
    public function setKeepAlive(int $interval): void
    {
        $this->keepAlive = $interval;
    }

    /**
     * Get the output from stdError
     */
    public function getStdError(): string
    {
        return $this->stdErrorLog;
    }

    /**
     * Execute Command
     *
     * If $callback is set to false then \phpseclib3\Net\SSH2::get_channel_packet(self::CHANNEL_EXEC) will need to be called manually.
     * In all likelihood, this is not a feature you want to be taking advantage of.
     *
     * @return string|bool
     * @psalm-return ($callback is callable ? bool : string|bool)
     * @throws RuntimeException on connection error
     */
    public function exec(string $command, callable $callback = null)
    {
        $this->curTimeout = $this->timeout;
        $this->is_timeout = false;
        $this->stdErrorLog = '';

        if (!$this->isAuthenticated()) {
            return false;
        }

        //if ($this->isPTYOpen()) {
        //    throw new RuntimeException('If you want to run multiple exec()\'s you will need to disable (and re-enable if appropriate) a PTY for each one.');
        //}

        $this->open_channel(self::CHANNEL_EXEC);

        if ($this->request_pty === true) {
            $terminal_modes = pack('C', TerminalMode::TTY_OP_END);
            $packet = Strings::packSSH2(
                'CNsCsN4s',
                MessageType::CHANNEL_REQUEST,
                $this->server_channels[self::CHANNEL_EXEC],
                'pty-req',
                1,
                $this->term,
                $this->windowColumns,
                $this->windowRows,
                0,
                0,
                $terminal_modes
            );

            $this->send_binary_packet($packet);

            $this->channel_status[self::CHANNEL_EXEC] = MessageType::CHANNEL_REQUEST;
            if (!$this->get_channel_packet(self::CHANNEL_EXEC)) {
                $this->disconnect_helper(DisconnectReason::BY_APPLICATION);
                throw new RuntimeException('Unable to request pseudo-terminal');
            }
        }

        // sending a pty-req SSH_MSG_CHANNEL_REQUEST message is unnecessary and, in fact, in most cases, slows things
        // down.  the one place where it might be desirable is if you're doing something like \phpseclib3\Net\SSH2::exec('ping localhost &').
        // with a pty-req SSH_MSG_CHANNEL_REQUEST, exec() will return immediately and the ping process will then
        // then immediately terminate.  without such a request exec() will loop indefinitely.  the ping process won't end but
        // neither will your script.

        // although, in theory, the size of SSH_MSG_CHANNEL_REQUEST could exceed the maximum packet size established by
        // SSH_MSG_CHANNEL_OPEN_CONFIRMATION, RFC4254#section-5.1 states that the "maximum packet size" refers to the
        // "maximum size of an individual data packet". ie. SSH_MSG_CHANNEL_DATA.  RFC4254#section-5.2 corroborates.
        $packet = Strings::packSSH2(
            'CNsCs',
            MessageType::CHANNEL_REQUEST,
            $this->server_channels[self::CHANNEL_EXEC],
            'exec',
            1,
            $command
        );
        $this->send_binary_packet($packet);

        $this->channel_status[self::CHANNEL_EXEC] = MessageType::CHANNEL_REQUEST;

        if (!$this->get_channel_packet(self::CHANNEL_EXEC)) {
            return false;
        }

        $this->channel_status[self::CHANNEL_EXEC] = MessageType::CHANNEL_DATA;

        if ($this->request_pty === true) {
            $this->channel_id_last_interactive = self::CHANNEL_EXEC;
            return true;
        }

        $output = '';
        while (true) {
            $temp = $this->get_channel_packet(self::CHANNEL_EXEC);
            switch (true) {
                case $temp === true:
                    return is_callable($callback) ? true : $output;
                case $temp === false:
                    return false;
                default:
                    if (is_callable($callback)) {
                        if ($callback($temp) === true) {
                            $this->close_channel(self::CHANNEL_EXEC);
                            return true;
                        }
                    } else {
                        $output .= $temp;
                    }
            }
        }
    }

    /**
     * How many channels are currently open?
     *
     * @return int
     */
    public function getOpenChannelCount()
    {
        return $this->channelCount;
    }

    /**
     * Opens a channel
     */
    protected function open_channel(int $channel, bool $skip_extended = false): bool
    {
        if (isset($this->channel_status[$channel]) && $this->channel_status[$channel] != MessageType::CHANNEL_CLOSE) {
            throw new RuntimeException('Please close the channel (' . $channel . ') before trying to open it again');
        }

        $this->channelCount++;

        if ($this->channelCount > 1 && $this->errorOnMultipleChannels) {
            throw new RuntimeException("Ubuntu's OpenSSH from 5.8 to 6.9 doesn't work with multiple channels");
        }

        // RFC4254 defines the (client) window size as "bytes the other party can send before it must wait for the window to
        // be adjusted".  0x7FFFFFFF is, at 2GB, the max size.  technically, it should probably be decremented, but,
        // honestly, if you're transferring more than 2GB, you probably shouldn't be using phpseclib, anyway.
        // see http://tools.ietf.org/html/rfc4254#section-5.2 for more info
        $this->window_size_server_to_client[$channel] = $this->window_size;
        // 0x8000 is the maximum max packet size, per http://tools.ietf.org/html/rfc4253#section-6.1, although since PuTTy
        // uses 0x4000, that's what will be used here, as well.
        $packet_size = 0x4000;

        $packet = Strings::packSSH2(
            'CsN3',
            MessageType::CHANNEL_OPEN,
            'session',
            $channel,
            $this->window_size_server_to_client[$channel],
            $packet_size
        );

        $this->send_binary_packet($packet);

        $this->channel_status[$channel] = MessageType::CHANNEL_OPEN;

        return $this->get_channel_packet($channel, $skip_extended);
    }

    /**
     * Creates an interactive shell
     *
     * Returns bool(true) if the shell was opened.
     * Returns bool(false) if the shell was already open.
     *
     * @throws InsufficientSetupException if not authenticated
     * @throws UnexpectedValueException on receipt of unexpected packets
     * @throws RuntimeException on other errors
     * @see self::isShellOpen()
     * @see self::read()
     * @see self::write()
     */
    public function openShell(): bool
    {
        if (!$this->isAuthenticated()) {
            throw new InsufficientSetupException('Operation disallowed prior to login()');
        }

        $this->open_channel(self::CHANNEL_SHELL);

        $terminal_modes = pack('C', TerminalMode::TTY_OP_END);
        $packet = Strings::packSSH2(
            'CNsbsN4s',
            MessageType::CHANNEL_REQUEST,
            $this->server_channels[self::CHANNEL_SHELL],
            'pty-req',
            true, // want reply
            $this->term,
            $this->windowColumns,
            $this->windowRows,
            0,
            0,
            $terminal_modes
        );

        $this->send_binary_packet($packet);

        $this->channel_status[self::CHANNEL_SHELL] = MessageType::CHANNEL_REQUEST;

        if (!$this->get_channel_packet(self::CHANNEL_SHELL)) {
            throw new RuntimeException('Unable to request pty');
        }

        $packet = Strings::packSSH2(
            'CNsb',
            MessageType::CHANNEL_REQUEST,
            $this->server_channels[self::CHANNEL_SHELL],
            'shell',
            true // want reply
        );
        $this->send_binary_packet($packet);

        $response = $this->get_channel_packet(self::CHANNEL_SHELL);
        if ($response === false) {
            throw new RuntimeException('Unable to request shell');
        }

        $this->channel_status[self::CHANNEL_SHELL] = MessageType::CHANNEL_DATA;

        $this->channel_id_last_interactive = self::CHANNEL_SHELL;

        $this->bitmap |= self::MASK_SHELL;

        return true;
    }

    /**
     * Return the channel to be used with read(), write(), and reset(), if none were specified
     * @deprecated for lack of transparency in intended channel target, to be potentially replaced
     *             with method which guarantees open-ness of all yielded channels and throws
     *             error for multiple open channels
     * @see self::read()
     * @see self::write()
     */
    private function get_interactive_channel(): int
    {
        switch (true) {
            case $this->is_channel_status_data(self::CHANNEL_SUBSYSTEM):
                return self::CHANNEL_SUBSYSTEM;
            case $this->is_channel_status_data(self::CHANNEL_EXEC):
                return self::CHANNEL_EXEC;
            default:
                return self::CHANNEL_SHELL;
        }
    }

    /**
     * Indicates the DATA status on the given channel
     */
    private function is_channel_status_data(int $channel): bool
    {
        return isset($this->channel_status[$channel]) && $this->channel_status[$channel] == MessageType::CHANNEL_DATA;
    }

    /**
     * Return an available open channel
     *
     * @return int
     */
    private function get_open_channel()
    {
        $channel = self::CHANNEL_EXEC;
        do {
            if (isset($this->channel_status[$channel]) && $this->channel_status[$channel] == MessageType::CHANNEL_OPEN) {
                return $channel;
            }
        } while ($channel++ < self::CHANNEL_SUBSYSTEM);

        return false;
    }

    /**
     * Request agent forwarding of remote server
     */
    public function requestAgentForwarding(): bool
    {
        $request_channel = $this->get_open_channel();
        if ($request_channel === false) {
            return false;
        }

        $packet = Strings::packSSH2(
            'CNsC',
            MessageType::CHANNEL_REQUEST,
            $this->server_channels[$request_channel],
            'auth-agent-req@openssh.com',
            1
        );

        $this->channel_status[$request_channel] = MessageType::CHANNEL_REQUEST;

        $this->send_binary_packet($packet);

        if (!$this->get_channel_packet($request_channel)) {
            return false;
        }

        $this->channel_status[$request_channel] = MessageType::CHANNEL_OPEN;

        return true;
    }

    /**
     * Returns the output of an interactive shell
     *
     * Returns when there's a match for $expect, which can take the form of a string literal or,
     * if $mode == self::READ_REGEX, a regular expression.
     *
     * If not specifying a channel, an open interactive channel will be selected, or, if there are
     * no open channels, an interactive shell will be created. If there are multiple open
     * interactive channels, a legacy behavior will apply in which channel selection prioritizes
     * an active subsystem, the exec pty, and, lastly, the shell. If using multiple interactive
     * channels, callers are discouraged from relying on this legacy behavior and should specify
     * the intended channel.
     *
     * @param int $mode One of the self::READ_* constants
     * @param int|null $channel Channel id returned by self::getInteractiveChannelId()
     * @return string|bool|null
     * @throws RuntimeException on connection error
     * @throws InsufficientSetupException on unexpected channel status, possibly due to closure
     * @see self::write()
     */
    public function read(string $expect = '', int $mode = self::READ_SIMPLE, int $channel = null)
    {
        if (!$this->isAuthenticated()) {
            throw new InsufficientSetupException('Operation disallowed prior to login()');
        }

        $this->curTimeout = $this->timeout;
        $this->is_timeout = false;

        if ($channel === null) {
            $channel = $this->get_interactive_channel();
        }

        if (!$this->is_channel_status_data($channel) && empty($this->channel_buffers[$channel])) {
            if ($channel != self::CHANNEL_SHELL) {
                throw new InsufficientSetupException('Data is not available on channel');
            } elseif (!$this->openShell()) {
                throw new RuntimeException('Unable to initiate an interactive shell session');
            }
        }

        if ($mode == self::READ_NEXT) {
            return $this->get_channel_packet($channel);
        }

        $match = $expect;
        while (true) {
            if ($mode == self::READ_REGEX) {
                preg_match($expect, substr($this->interactiveBuffer, -1024), $matches);
                $match = $matches[0] ?? '';
            }
            $pos = strlen($match) ? strpos($this->interactiveBuffer, $match) : false;
            if ($pos !== false) {
                return Strings::shift($this->interactiveBuffer, $pos + strlen($match));
            }
            $response = $this->get_channel_packet($channel);
            if ($response === true) {
                return Strings::shift($this->interactiveBuffer, strlen($this->interactiveBuffer));
            }

            $this->interactiveBuffer .= $response;
        }
    }

    /**
     * Inputs a command into an interactive shell.
     *
     * If not specifying a channel, an open interactive channel will be selected, or, if there are
     * no open channels, an interactive shell will be created. If there are multiple open
     * interactive channels, a legacy behavior will apply in which channel selection prioritizes
     * an active subsystem, the exec pty, and, lastly, the shell. If using multiple interactive
     * channels, callers are discouraged from relying on this legacy behavior and should specify
     * the intended channel.
     *
     * @param int|null $channel Channel id returned by self::getInteractiveChannelId()
     * @throws RuntimeException on connection error
     * @throws InsufficientSetupException on unexpected channel status, possibly due to closure
     * @see SSH2::read()
     */
    public function write(string $cmd, int $channel = null): void
    {
        if (!$this->isAuthenticated()) {
            throw new InsufficientSetupException('Operation disallowed prior to login()');
        }

        if ($channel === null) {
            $channel = $this->get_interactive_channel();
        }

        if (!$this->is_channel_status_data($channel)) {
            if ($channel != self::CHANNEL_SHELL) {
                throw new InsufficientSetupException('Data is not available on channel');
            } elseif (!$this->openShell()) {
                throw new RuntimeException('Unable to initiate an interactive shell session');
            }
        }

        $this->send_channel_packet($channel, $cmd);
    }

    /**
     * Start a subsystem.
     *
     * Right now only one subsystem at a time is supported. To support multiple subsystem's stopSubsystem() could accept
     * a string that contained the name of the subsystem, but at that point, only one subsystem of each type could be opened.
     * To support multiple subsystem's of the same name maybe it'd be best if startSubsystem() generated a new channel id and
     * returns that and then that that was passed into stopSubsystem() but that'll be saved for a future date and implemented
     * if there's sufficient demand for such a feature.
     *
          * @see self::stopSubsystem()
     */
    public function startSubsystem(string $subsystem): bool
    {
        $this->open_channel(self::CHANNEL_SUBSYSTEM);

        $packet = Strings::packSSH2(
            'CNsCs',
            MessageType::CHANNEL_REQUEST,
            $this->server_channels[self::CHANNEL_SUBSYSTEM],
            'subsystem',
            1,
            $subsystem
        );
        $this->send_binary_packet($packet);

        $this->channel_status[self::CHANNEL_SUBSYSTEM] = MessageType::CHANNEL_REQUEST;

        if (!$this->get_channel_packet(self::CHANNEL_SUBSYSTEM)) {
            return false;
        }

        $this->channel_status[self::CHANNEL_SUBSYSTEM] = MessageType::CHANNEL_DATA;

        $this->channel_id_last_interactive = self::CHANNEL_SUBSYSTEM;

        return true;
    }

    /**
     * Stops a subsystem.
     *
     * @see self::startSubsystem()
     */
    public function stopSubsystem(): bool
    {
        if ($this->isInteractiveChannelOpen(self::CHANNEL_SUBSYSTEM)) {
            $this->close_channel(self::CHANNEL_SUBSYSTEM);
        }
        return true;
    }

    /**
     * Closes a channel
     *
     * If read() timed out you might want to just close the channel and have it auto-restart on the next read() call
     *
     * If not specifying a channel, an open interactive channel will be selected. If there are
     * multiple open interactive channels, a legacy behavior will apply in which channel selection
     * prioritizes an active subsystem, the exec pty, and, lastly, the shell. If using multiple
     * interactive channels, callers are discouraged from relying on this legacy behavior and
     * should specify the intended channel.
     *
     * @param int|null $channel Channel id returned by self::getInteractiveChannelId()
     */
    public function reset(int $channel = null): void
    {
        if ($channel === null) {
            $channel = $this->get_interactive_channel();
        }
        if ($this->isInteractiveChannelOpen($channel)) {
            $this->close_channel($channel);
        }
    }

    /**
     * Is timeout?
     *
     * Did exec() or read() return because they timed out or because they encountered the end?
     */
    public function isTimeout(): bool
    {
        return $this->is_timeout;
    }

    /**
     * Disconnect
     */
    public function disconnect(): void
    {
        $this->disconnect_helper(DisconnectReason::BY_APPLICATION);
        if (isset($this->realtime_log_file) && is_resource($this->realtime_log_file)) {
            fclose($this->realtime_log_file);
        }
        unset(self::$connections[$this->getResourceId()]);
    }

    /**
     * Destructor.
     *
     * Will be called, automatically, if you're supporting just PHP5.  If you're supporting PHP4, you'll need to call
     * disconnect().
     */
    public function __destruct()
    {
        $this->disconnect();
    }

    /**
     * Is the connection still active?
     *
     * $level has 3x possible values:
     * 0 (default): phpseclib takes a passive approach to see if the connection is still active by calling feof()
     *    on the socket
     * 1: phpseclib takes an active approach to see if the connection is still active by sending an SSH_MSG_IGNORE
     *    packet that doesn't require a response
     * 2: phpseclib takes an active approach to see if the connection is still active by sending an SSH_MSG_CHANNEL_OPEN
     *    packet and imediately trying to close that channel. some routers, in particular, however, will only let you
     *    open one channel, so this approach could yield false positives
     *
     * @param int $level
     * @return bool
     */
    public function isConnected(int $level = 0): bool
    {
        if ($level < 0 || $level > 2) {
            throw new InvalidArgumentException('$level must be 0, 1 or 2');
        }

        if ($level == 0) {
            return ($this->bitmap & self::MASK_CONNECTED) && is_resource($this->fsock) && !feof($this->fsock);
        }
        try {
            if ($level == 1) {
                $this->send_binary_packet(pack('CN', NET_SSH2_MSG_IGNORE, 0));
            } else {
                $this->open_channel(self::CHANNEL_KEEP_ALIVE);
                $this->close_channel(self::CHANNEL_KEEP_ALIVE);
            }
            return true;
        } catch (\Exception $e) {
            return false;
        }
    }

    /**
     * Have you successfully been logged in?
     */
    public function isAuthenticated(): bool
    {
        return (bool) ($this->bitmap & self::MASK_LOGIN);
    }

    /**
     * Is the interactive shell active?
     */
    public function isShellOpen(): bool
    {
        return $this->isInteractiveChannelOpen(self::CHANNEL_SHELL);
    }

    /**
     * Is the exec pty active?
     */
    public function isPTYOpen(): bool
    {
        return $this->isInteractiveChannelOpen(self::CHANNEL_EXEC);
    }

    /**
     * Is the given interactive channel active?
     *
     * @param int $channel Channel id returned by self::getInteractiveChannelId()
     */
    public function isInteractiveChannelOpen(int $channel): bool
    {
        return $this->isAuthenticated() && $this->is_channel_status_data($channel);
    }

    /**
     * Returns a channel identifier, presently of the last interactive channel opened, regardless of current status.
     * Returns 0 if no interactive channel has been opened.
     *
     * @see self::isInteractiveChannelOpen()
     */
    public function getInteractiveChannelId(): int
    {
        return $this->channel_id_last_interactive;
    }

    /**
     * Pings a server connection, or tries to reconnect if the connection has gone down
     *
     * Inspired by http://php.net/manual/en/mysqli.ping.php
     */
    public function ping(): bool
    {
        if (!$this->isAuthenticated()) {
            if (!empty($this->auth)) {
                return $this->reconnect();
            }
            return false;
        }

        try {
            $this->open_channel(self::CHANNEL_KEEP_ALIVE);
        } catch (\RuntimeException $e) {
            return $this->reconnect();
        }

        $this->close_channel(self::CHANNEL_KEEP_ALIVE);
        return true;
    }

    /**
     * In situ reconnect method
     *
     * @return boolean
     */
    private function reconnect(): bool
    {
        $this->reset_connection(DisconnectReason::CONNECTION_LOST);
        $this->retry_connect = true;
        $this->connect();
        foreach ($this->auth as $auth) {
            $result = $this->login(...$auth);
        }
        return $result;
    }

    /**
     * Resets a connection for re-use
     */
    protected function reset_connection(int $reason): void
    {
        $this->disconnect_helper($reason);
        $this->decrypt = $this->encrypt = false;
        $this->decrypt_block_size = $this->encrypt_block_size = 8;
        $this->hmac_check = $this->hmac_create = false;
        $this->hmac_size = false;
        $this->session_id = false;
        $this->retry_connect = true;
        $this->get_seq_no = $this->send_seq_no = 0;
        $this->channel_status = [];
        $this->channel_id_last_interactive = 0;
    }

    /**
     * Gets Binary Packets
     *
     * See '6. Binary Packet Protocol' of rfc4253 for more info.
     *
     * @return bool|string
     * @see self::_send_binary_packet()
     */
    private function get_binary_packet(bool $skip_channel_filter = false)
    {
        if ($skip_channel_filter) {
            if (!is_resource($this->fsock)) {
                throw new InvalidArgumentException('fsock is not a resource.');
            }
            $read = [$this->fsock];
            $write = $except = null;

            if (!$this->curTimeout) {
                if ($this->keepAlive <= 0) {
                    static::stream_select($read, $write, $except, null);
                } else {
                    if (!static::stream_select($read, $write, $except, $this->keepAlive)) {
                        $this->send_binary_packet(pack('CN', MessageType::IGNORE, 0));
                        return $this->get_binary_packet(true);
                    }
                }
            } else {
                if ($this->curTimeout < 0) {
                    $this->is_timeout = true;
                    return true;
                }

                $start = microtime(true);

                if ($this->keepAlive > 0 && $this->keepAlive < $this->curTimeout) {
                    if (!static::stream_select($read, $write, $except, $this->keepAlive)) {
                        $this->send_binary_packet(pack('CN', MessageType::IGNORE, 0));
                        $elapsed = microtime(true) - $start;
                        $this->curTimeout -= $elapsed;
                        return $this->get_binary_packet(true);
                    }
                    $elapsed = microtime(true) - $start;
                    $this->curTimeout -= $elapsed;
                }

                $sec = (int) floor($this->curTimeout);
                $usec = (int) (1000000 * ($this->curTimeout - $sec));

                // this can return a "stream_select(): unable to select [4]: Interrupted system call" error
                if (!static::stream_select($read, $write, $except, $sec, $usec)) {
                    $this->is_timeout = true;
                    return true;
                }
                $elapsed = microtime(true) - $start;
                $this->curTimeout -= $elapsed;
            }
        }

        if (!is_resource($this->fsock) || feof($this->fsock)) {
            $this->bitmap = 0;
            $str = 'Connection closed (by server) prematurely';
            if (isset($elapsed)) {
                $str .= ' ' . $elapsed . 's';
            }
            throw new ConnectionClosedException($str);
        }

        $start = microtime(true);
        $sec = (int) floor($this->curTimeout);
        $usec = (int) (1000000 * ($this->curTimeout - $sec));
        stream_set_timeout($this->fsock, $sec, $usec);
        $raw = stream_get_contents($this->fsock, $this->decrypt_block_size);

        if (!strlen($raw)) {
            $this->bitmap = 0;
            throw new ConnectionClosedException('No data received from server');
        }

        if ($this->decrypt) {
            switch ($this->decryptName) {
                case 'aes128-gcm@openssh.com':
                case 'aes256-gcm@openssh.com':
                    $this->decrypt->setNonce(
                        $this->decryptFixedPart .
                        $this->decryptInvocationCounter
                    );
                    Strings::increment_str($this->decryptInvocationCounter);
                    $this->decrypt->setAAD($temp = Strings::shift($raw, 4));
                    extract(unpack('Npacket_length', $temp));
                    /**
                     * @var integer $packet_length
                     */

                    $raw .= $this->read_remaining_bytes($packet_length - $this->decrypt_block_size + 4);
                    $stop = microtime(true);
                    $tag = stream_get_contents($this->fsock, $this->decrypt_block_size);
                    $this->decrypt->setTag($tag);
                    $raw = $this->decrypt->decrypt($raw);
                    $raw = $temp . $raw;
                    $remaining_length = 0;
                    break;
                case 'chacha20-poly1305@openssh.com':
                    // This should be impossible, but we are checking anyway to narrow the type for Psalm.
                    if (!($this->decrypt instanceof ChaCha20)) {
                        throw new LogicException('$this->decrypt is not a ' . ChaCha20::class);
                    }

                    $nonce = pack('N2', 0, $this->get_seq_no);

                    $this->lengthDecrypt->setNonce($nonce);
                    $temp = $this->lengthDecrypt->decrypt($aad = Strings::shift($raw, 4));
                    extract(unpack('Npacket_length', $temp));
                    /**
                     * @var integer $packet_length
                     */

                    $raw .= $this->read_remaining_bytes($packet_length - $this->decrypt_block_size + 4);
                    $stop = microtime(true);
                    $tag = stream_get_contents($this->fsock, 16);

                    $this->decrypt->setNonce($nonce);
                    $this->decrypt->setCounter(0);
                    // this is the same approach that's implemented in Salsa20::createPoly1305Key()
                    // but we don't want to use the same AEAD construction that RFC8439 describes
                    // for ChaCha20-Poly1305 so we won't rely on it (see Salsa20::poly1305())
                    $this->decrypt->setPoly1305Key(
                        $this->decrypt->encrypt(str_repeat("\0", 32))
                    );
                    $this->decrypt->setAAD($aad);
                    $this->decrypt->setCounter(1);
                    $this->decrypt->setTag($tag);
                    $raw = $this->decrypt->decrypt($raw);
                    $raw = $temp . $raw;
                    $remaining_length = 0;
                    break;
                default:
                    if (!$this->hmac_check instanceof Hash || !$this->hmac_check_etm) {
                        $raw = $this->decrypt->decrypt($raw);
                        break;
                    }
                    extract(unpack('Npacket_length', $temp = Strings::shift($raw, 4)));
                    /**
                     * @var integer $packet_length
                     */
                    $raw .= $this->read_remaining_bytes($packet_length - $this->decrypt_block_size + 4);
                    $stop = microtime(true);
                    $encrypted = $temp . $raw;
                    $raw = $temp . $this->decrypt->decrypt($raw);
                    $remaining_length = 0;
            }
        }

        if (strlen($raw) < 5) {
            $this->bitmap = 0;
            throw new RuntimeException('Plaintext is too short');
        }
        extract(unpack('Npacket_length/Cpadding_length', Strings::shift($raw, 5)));
        /**
         * @var integer $packet_length
         * @var integer $padding_length
         */

        if (!isset($remaining_length)) {
            $remaining_length = $packet_length + 4 - $this->decrypt_block_size;
        }

        $buffer = $this->read_remaining_bytes($remaining_length);

        if (!isset($stop)) {
            $stop = microtime(true);
        }
        if (strlen($buffer)) {
            $raw .= $this->decrypt ? $this->decrypt->decrypt($buffer) : $buffer;
        }

        $payload = Strings::shift($raw, $packet_length - $padding_length - 1);
        $padding = Strings::shift($raw, $padding_length); // should leave $raw empty

        if ($this->hmac_check instanceof Hash) {
            $hmac = stream_get_contents($this->fsock, $this->hmac_size);
            if ($hmac === false || strlen($hmac) != $this->hmac_size) {
                $this->disconnect_helper(DisconnectReason::MAC_ERROR);
                throw new RuntimeException('Error reading socket');
            }

            $reconstructed = !$this->hmac_check_etm ?
                pack('NCa*', $packet_length, $padding_length, $payload . $padding) :
                $encrypted;
            if (($this->hmac_check->getHash() & "\xFF\xFF\xFF\xFF") == 'umac') {
                $this->hmac_check->setNonce("\0\0\0\0" . pack('N', $this->get_seq_no));
                if ($hmac != $this->hmac_check->hash($reconstructed)) {
                    $this->disconnect_helper(DisconnectReason::MAC_ERROR);
                    throw new RuntimeException('Invalid UMAC');
                }
            } else {
                if ($hmac != $this->hmac_check->hash(pack('Na*', $this->get_seq_no, $reconstructed))) {
                    $this->disconnect_helper(DisconnectReason::MAC_ERROR);
                    throw new RuntimeException('Invalid HMAC');
                }
            }
        }

        switch ($this->decompress) {
            case self::NET_SSH2_COMPRESSION_ZLIB_AT_OPENSSH:
                if (!$this->isAuthenticated()) {
                    break;
                }
                // fall-through
            case self::NET_SSH2_COMPRESSION_ZLIB:
                if ($this->regenerate_decompression_context) {
                    $this->regenerate_decompression_context = false;

                    $cmf = ord($payload[0]);
                    $cm = $cmf & 0x0F;
                    if ($cm != 8) { // deflate
                        throw new UnsupportedAlgorithmException("Only CM = 8 ('deflate') is supported ($cm)");
                    }
                    $cinfo = ($cmf & 0xF0) >> 4;
                    if ($cinfo > 7) {
                        throw new RuntimeException("CINFO above 7 is not allowed ($cinfo)");
                    }
                    $windowSize = 1 << ($cinfo + 8);

                    $flg = ord($payload[1]);
                    //$fcheck = $flg && 0x0F;
                    if ((($cmf << 8) | $flg) % 31) {
                        throw new RuntimeException('fcheck failed');
                    }
                    $fdict = boolval($flg & 0x20);
                    $flevel = ($flg & 0xC0) >> 6;

                    $this->decompress_context = inflate_init(ZLIB_ENCODING_RAW, ['window' => $cinfo + 8]);
                    $payload = substr($payload, 2);
                }
                if ($this->decompress_context) {
                    $payload = inflate_add($this->decompress_context, $payload, ZLIB_PARTIAL_FLUSH);
                }
        }

        $this->get_seq_no++;

        if (defined('NET_SSH2_LOGGING')) {
            $current = microtime(true);
            $message_number = sprintf(
                '<- %s (since last: %s, network: %ss)',
                ($constantName = MessageType::findConstantNameByValue($value = ord($payload[0])))
                    ? "SSH_MSG_$constantName"
                    : "UNKNOWN ($value)",
                round($current - $this->last_packet, 4),
                round($stop - $start, 4)
            );
            $this->append_log($message_number, $payload);
            $this->last_packet = $current;
        }

        return $this->filter($payload, $skip_channel_filter);
    }

    /**
     * Read Remaining Bytes
     *
     * @return string
     * @see self::get_binary_packet()
     */
    private function read_remaining_bytes(int $remaining_length)
    {
        if (!$remaining_length) {
            return '';
        }

        $adjustLength = false;
        if ($this->decrypt) {
            switch (true) {
                case $this->decryptName == 'aes128-gcm@openssh.com':
                case $this->decryptName == 'aes256-gcm@openssh.com':
                case $this->decryptName == 'chacha20-poly1305@openssh.com':
                case $this->hmac_check instanceof Hash && $this->hmac_check_etm:
                    $remaining_length += $this->decrypt_block_size - 4;
                    $adjustLength = true;
            }
        }

        // quoting <http://tools.ietf.org/html/rfc4253#section-6.1>,
        // "implementations SHOULD check that the packet length is reasonable"
        // PuTTY uses 0x9000 as the actual max packet size and so to shall we
        // don't do this when GCM mode is used since GCM mode doesn't encrypt the length
        if ($remaining_length < -$this->decrypt_block_size || $remaining_length > 0x9000 || $remaining_length % $this->decrypt_block_size != 0) {
            if (!$this->bad_key_size_fix && self::bad_algorithm_candidate($this->decrypt ? $this->decryptName : '') && !($this->bitmap & SSH2::MASK_LOGIN)) {
                $this->bad_key_size_fix = true;
                $this->reset_connection(DisconnectReason::KEY_EXCHANGE_FAILED);
                return false;
            }
            throw new RuntimeException('Invalid size');
        }

        if ($adjustLength) {
            $remaining_length -= $this->decrypt_block_size - 4;
        }

        $buffer = '';
        while ($remaining_length > 0) {
            $temp = stream_get_contents($this->fsock, $remaining_length);
            if ($temp === false || feof($this->fsock)) {
                $this->disconnect_helper(DisconnectReason::CONNECTION_LOST);
                throw new RuntimeException('Error reading from socket');
            }
            $buffer .= $temp;
            $remaining_length -= strlen($temp);
        }

        return $buffer;
    }

    /**
     * Filter Binary Packets
     *
     * Because some binary packets need to be ignored...
     *
     * @return string|bool
     * @see self::_get_binary_packet()
     */
    private function filter(string $payload, bool $skip_channel_filter)
    {
        switch (ord($payload[0])) {
            case MessageType::DISCONNECT:
                Strings::shift($payload, 1);
                [$reason_code, $message] = Strings::unpackSSH2('Ns', $payload);
                $this->errors[] = 'SSH_MSG_DISCONNECT: SSH_DISCONNECT_' . DisconnectReason::getConstantNameByValue($reason_code) . "\r\n$message";
                $this->bitmap = 0;
                return false;
            case MessageType::IGNORE:
                $this->extra_packets++;
                $payload = $this->get_binary_packet($skip_channel_filter);
                break;
            case MessageType::DEBUG:
                $this->extra_packets++;
                Strings::shift($payload, 2); // second byte is "always_display"
                [$message] = Strings::unpackSSH2('s', $payload);
                $this->errors[] = "SSH_MSG_DEBUG: $message";
                $payload = $this->get_binary_packet($skip_channel_filter);
                break;
            case MessageType::UNIMPLEMENTED:
                return false;
            case MessageType::KEXINIT:
                // this is here for key re-exchanges after the initial key exchange
                if ($this->session_id !== false) {
                    if (!$this->key_exchange($payload)) {
                        $this->bitmap = 0;
                        return false;
                    }
                    $payload = $this->get_binary_packet($skip_channel_filter);
                }
        }

        // see http://tools.ietf.org/html/rfc4252#section-5.4; only called when the encryption has been activated and when we haven't already logged in
        if (($this->bitmap & self::MASK_CONNECTED) && !$this->isAuthenticated() && !is_bool($payload) && ord($payload[0]) == MessageType::USERAUTH_BANNER) {
            Strings::shift($payload, 1);
            [$this->banner_message] = Strings::unpackSSH2('s', $payload);
            $payload = $this->get_binary_packet();
        }

        // only called when we've already logged in
        if (($this->bitmap & self::MASK_CONNECTED) && $this->isAuthenticated()) {
            if (is_bool($payload)) {
                return $payload;
            }

            switch (ord($payload[0])) {
                case MessageType::CHANNEL_REQUEST:
                    if (strlen($payload) == 31) {
                        extract(unpack('cpacket_type/Nchannel/Nlength', $payload));
                        if (substr($payload, 9, $length) == 'keepalive@openssh.com' && isset($this->server_channels[$channel])) {
                            if (ord(substr($payload, 9 + $length))) { // want reply
                                $this->send_binary_packet(pack('CN', MessageType::CHANNEL_SUCCESS, $this->server_channels[$channel]));
                            }
                            $payload = $this->get_binary_packet($skip_channel_filter);
                        }
                    }
                    break;
                case MessageType::CHANNEL_DATA:
                case MessageType::CHANNEL_EXTENDED_DATA:
                case MessageType::CHANNEL_CLOSE:
                case MessageType::CHANNEL_EOF:
                    if (!$skip_channel_filter && !empty($this->server_channels)) {
                        $this->binary_packet_buffer = $payload;
                        $this->get_channel_packet(true);
                        $payload = $this->get_binary_packet();
                    }
                    break;
                case MessageType::GLOBAL_REQUEST: // see http://tools.ietf.org/html/rfc4254#section-4
                    Strings::shift($payload, 1);
                    [$request_name] = Strings::unpackSSH2('s', $payload);
                    $this->errors[] = "SSH_MSG_GLOBAL_REQUEST: $request_name";

                    try {
                        $this->send_binary_packet(pack('C', MessageType::REQUEST_FAILURE));
                    } catch (\RuntimeException $e) {
                        return $this->disconnect_helper(DisconnectReason::BY_APPLICATION);
                    }

                    $payload = $this->get_binary_packet($skip_channel_filter);
                    break;
                case MessageType::CHANNEL_OPEN: // see http://tools.ietf.org/html/rfc4254#section-5.1
                    Strings::shift($payload, 1);
                    [$data, $server_channel] = Strings::unpackSSH2('sN', $payload);
                    switch ($data) {
                        case 'auth-agent':
                        case 'auth-agent@openssh.com':
                            if (isset($this->agent)) {
                                $new_channel = self::CHANNEL_AGENT_FORWARD;

                                [
                                    $remote_window_size,
                                    $remote_maximum_packet_size
                                ] = Strings::unpackSSH2('NN', $payload);

                                $this->packet_size_client_to_server[$new_channel] = $remote_window_size;
                                $this->window_size_server_to_client[$new_channel] = $remote_maximum_packet_size;
                                $this->window_size_client_to_server[$new_channel] = $this->window_size;

                                $packet_size = 0x4000;

                                $packet = pack(
                                    'CN4',
                                    MessageType::CHANNEL_OPEN_CONFIRMATION,
                                    $server_channel,
                                    $new_channel,
                                    $packet_size,
                                    $packet_size
                                );

                                $this->server_channels[$new_channel] = $server_channel;
                                $this->channel_status[$new_channel] = MessageType::CHANNEL_OPEN_CONFIRMATION;
                                $this->send_binary_packet($packet);
                            }
                            break;
                        default:
                            $packet = Strings::packSSH2(
                                'CN2ss',
                                MessageType::CHANNEL_OPEN_FAILURE,
                                $server_channel,
                                ChannelConnectionFailureReason::ADMINISTRATIVELY_PROHIBITED,
                                '', // description
                                '' // language tag
                            );

                            try {
                                $this->send_binary_packet($packet);
                            } catch (\RuntimeException $e) {
                                return $this->disconnect_helper(DisconnectReason::BY_APPLICATION);
                            }
                    }

                    $payload = $this->get_binary_packet($skip_channel_filter);
                    break;
                case MessageType::CHANNEL_WINDOW_ADJUST:
                    Strings::shift($payload, 1);
                    [$channel, $window_size] = Strings::unpackSSH2('NN', $payload);

                    $this->window_size_client_to_server[$channel] += $window_size;

                    $payload = ($this->bitmap & self::MASK_WINDOW_ADJUST) ? true : $this->get_binary_packet($skip_channel_filter);
            }
        }

        return $payload;
    }

    /**
     * Enable Quiet Mode
     *
     * Suppress stderr from output
     */
    public function enableQuietMode(): void
    {
        $this->quiet_mode = true;
    }

    /**
     * Disable Quiet Mode
     *
     * Show stderr in output
     */
    public function disableQuietMode(): void
    {
        $this->quiet_mode = false;
    }

    /**
     * Returns whether Quiet Mode is enabled or not
     *
     * @see self::enableQuietMode()
     * @see self::disableQuietMode()
     */
    public function isQuietModeEnabled(): bool
    {
        return $this->quiet_mode;
    }

    /**
     * Enable request-pty when using exec()
     */
    public function enablePTY(): void
    {
        $this->request_pty = true;
    }

    /**
     * Disable request-pty when using exec()
     */
    public function disablePTY(): void
    {
        if ($this->isPTYOpen()) {
            $this->close_channel(self::CHANNEL_EXEC);
        }
        $this->request_pty = false;
    }

    /**
     * Returns whether request-pty is enabled or not
     *
     * @see self::enablePTY()
     * @see self::disablePTY()
     */
    public function isPTYEnabled(): bool
    {
        return $this->request_pty;
    }

    /**
     * Gets channel data
     *
     * Returns the data as a string. bool(true) is returned if:
     *
     * - the server closes the channel
     * - if the connection times out
     * - if the channel status is CHANNEL_OPEN and the response was CHANNEL_OPEN_CONFIRMATION
     * - if the channel status is CHANNEL_REQUEST and the response was CHANNEL_SUCCESS
     * - if the channel status is CHANNEL_CLOSE and the response was CHANNEL_CLOSE
     *
     * bool(false) is returned if:
     *
     * - if the channel status is CHANNEL_REQUEST and the response was CHANNEL_FAILURE
     *
     * @throws RuntimeException on connection error
     */
    protected function get_channel_packet(int $client_channel, bool $skip_extended = false)
    {
        if (!empty($this->channel_buffers[$client_channel])) {
            switch ($this->channel_status[$client_channel]) {
                case MessageType::CHANNEL_REQUEST:
                    foreach ($this->channel_buffers[$client_channel] as $i => $packet) {
                        switch (ord($packet[0])) {
                            case MessageType::CHANNEL_SUCCESS:
                            case MessageType::CHANNEL_FAILURE:
                                unset($this->channel_buffers[$client_channel][$i]);
                                return substr($packet, 1);
                        }
                    }
                    break;
                default:
                    return substr(array_shift($this->channel_buffers[$client_channel]), 1);
            }
        }

        while (true) {
            if ($this->binary_packet_buffer !== false) {
                $response = $this->binary_packet_buffer;
                $this->binary_packet_buffer = false;
            } else {
                $response = $this->get_binary_packet(true);
                if ($response === true && $this->is_timeout) {
                    if ($client_channel == self::CHANNEL_EXEC && !$this->request_pty) {
                        $this->close_channel($client_channel);
                    }
                    return true;
                }
                if ($response === false) {
                    $this->disconnect_helper(DisconnectReason::CONNECTION_LOST);
                    throw new ConnectionClosedException('Connection closed by server');
                }
            }

            if ($client_channel == -1 && $response === true) {
                return true;
            }
            [$type, $channel] = Strings::unpackSSH2('CN', $response);

            // will not be setup yet on incoming channel open request
            if (isset($channel) && isset($this->channel_status[$channel]) && isset($this->window_size_server_to_client[$channel])) {
                $this->window_size_server_to_client[$channel] -= strlen($response);

                // resize the window, if appropriate
                if ($this->window_size_server_to_client[$channel] < 0) {
                // PuTTY does something more analogous to the following:
                //if ($this->window_size_server_to_client[$channel] < 0x3FFFFFFF) {
                    $packet = pack('CNN', MessageType::CHANNEL_WINDOW_ADJUST, $this->server_channels[$channel], $this->window_resize);
                    $this->send_binary_packet($packet);
                    $this->window_size_server_to_client[$channel] += $this->window_resize;
                }

                switch ($type) {
                    case MessageType::CHANNEL_EXTENDED_DATA:
                        /*
                        if ($client_channel == self::CHANNEL_EXEC) {
                            $this->send_channel_packet($client_channel, chr(0));
                        }
                        */
                        // currently, there's only one possible value for $data_type_code: NET_SSH2_EXTENDED_DATA_STDERR
                        [$data_type_code, $data] = Strings::unpackSSH2('Ns', $response);
                        $this->stdErrorLog .= $data;
                        if ($skip_extended || $this->quiet_mode) {
                            continue 2;
                        }
                        if ($client_channel == $channel && $this->channel_status[$channel] == MessageType::CHANNEL_DATA) {
                            return $data;
                        }
                        $this->channel_buffers[$channel][] = chr($type) . $data;

                        continue 2;
                    case MessageType::CHANNEL_REQUEST:
                        if ($this->channel_status[$channel] == MessageType::CHANNEL_CLOSE) {
                            continue 2;
                        }
                        [$value] = Strings::unpackSSH2('s', $response);
                        switch ($value) {
                            case 'exit-signal':
                                [
                                    , // FALSE
                                    $signal_name,
                                    , // core dumped
                                    $error_message
                                ] = Strings::unpackSSH2('bsbs', $response);

                                $this->errors[] = "SSH_MSG_CHANNEL_REQUEST (exit-signal): $signal_name";
                                if (strlen($error_message)) {
                                    $this->errors[count($this->errors) - 1] .= "\r\n$error_message";
                                }

                                $this->send_binary_packet(pack('CN', MessageType::CHANNEL_EOF, $this->server_channels[$client_channel]));
                                $this->send_binary_packet(pack('CN', MessageType::CHANNEL_CLOSE, $this->server_channels[$channel]));

                                $this->channel_status[$channel] = MessageType::CHANNEL_EOF;

                                continue 3;
                            case 'exit-status':
                                [, $this->exit_status] = Strings::unpackSSH2('CN', $response);

                                // "The client MAY ignore these messages."
                                // -- http://tools.ietf.org/html/rfc4254#section-6.10

                                continue 3;
                            default:
                                // "Some systems may not implement signals, in which case they SHOULD ignore this message."
                                //  -- http://tools.ietf.org/html/rfc4254#section-6.9
                                continue 3;
                        }
                }

                switch ($this->channel_status[$channel]) {
                    case MessageType::CHANNEL_OPEN:
                        switch ($type) {
                            case MessageType::CHANNEL_OPEN_CONFIRMATION:
                                [
                                    $this->server_channels[$channel],
                                    $window_size,
                                    $this->packet_size_client_to_server[$channel]
                                ] = Strings::unpackSSH2('NNN', $response);

                                if ($window_size < 0) {
                                    $window_size &= 0x7FFFFFFF;
                                    $window_size += 0x80000000;
                                }
                                $this->window_size_client_to_server[$channel] = $window_size;
                                $result = $client_channel == $channel ? true : $this->get_channel_packet($client_channel, $skip_extended);
                                $this->on_channel_open();
                                return $result;
                            case MessageType::CHANNEL_OPEN_FAILURE:
                                $this->disconnect_helper(DisconnectReason::BY_APPLICATION);
                                throw new RuntimeException('Unable to open channel');
                            default:
                                if ($client_channel == $channel) {
                                    $this->disconnect_helper(DisconnectReason::BY_APPLICATION);
                                    throw new RuntimeException('Unexpected response to open request');
                                }
                                return $this->get_channel_packet($client_channel, $skip_extended);
                        }
                        break;
                    case MessageType::CHANNEL_REQUEST:
                        switch ($type) {
                            case MessageType::CHANNEL_SUCCESS:
                                return true;
                            case MessageType::CHANNEL_FAILURE:
                                return false;
                            case MessageType::CHANNEL_DATA:
                                [$data] = Strings::unpackSSH2('s', $response);
                                $this->channel_buffers[$channel][] = chr($type) . $data;
                                return $this->get_channel_packet($client_channel, $skip_extended);
                            default:
                                $this->disconnect_helper(DisconnectReason::BY_APPLICATION);
                                throw new RuntimeException('Unable to fulfill channel request');
                        }
                    case MessageType::CHANNEL_CLOSE:
                        if ($client_channel == $channel && $type == MessageType::CHANNEL_CLOSE) {
                            return true;
                        }
                        return $this->get_channel_packet($client_channel, $skip_extended);
                }
            }

            // ie. $this->channel_status[$channel] == MessageType::CHANNEL_DATA

            switch ($type) {
                case MessageType::CHANNEL_DATA:
                    /*
                    if ($channel == self::CHANNEL_EXEC) {
                        // SCP requires null packets, such as this, be sent.  further, in the case of the ssh.com SSH server
                        // this actually seems to make things twice as fast.  more to the point, the message right after
                        // SSH_MSG_CHANNEL_DATA (usually SSH_MSG_IGNORE) won't block for as long as it would have otherwise.
                        // in OpenSSH it slows things down but only by a couple thousandths of a second.
                        $this->send_channel_packet($channel, chr(0));
                    }
                    */
                    [$data] = Strings::unpackSSH2('s', $response);

                    if ($channel == self::CHANNEL_AGENT_FORWARD) {
                        $agent_response = $this->agent->forwardData($data);
                        if (!is_bool($agent_response)) {
                            $this->send_channel_packet($channel, $agent_response);
                        }
                        break;
                    }

                    if ($client_channel == $channel) {
                        return $data;
                    }
                    $this->channel_buffers[$channel][] = chr($type) . $data;
                    break;
                case MessageType::CHANNEL_CLOSE:
                    $this->curTimeout = 5;

                    $this->close_channel_bitmap($channel);

                    if ($this->channel_status[$channel] != MessageType::CHANNEL_EOF) {
                        $this->send_binary_packet(pack('CN', MessageType::CHANNEL_CLOSE, $this->server_channels[$channel]));
                    }

                    $this->channel_status[$channel] = MessageType::CHANNEL_CLOSE;
                    $this->channelCount--;

                    if ($client_channel == $channel) {
                        return true;
                    }
                    // fall-through
                case MessageType::CHANNEL_EOF:
                    break;
                default:
                    $this->disconnect_helper(DisconnectReason::BY_APPLICATION);
                    throw new RuntimeException("Error reading channel data ($type)");
            }
        }
    }

    /**
     * Sends Binary Packets
     *
     * See '6. Binary Packet Protocol' of rfc4253 for more info.
     *
     * @see self::_get_binary_packet()
     */
    protected function send_binary_packet(string $data, string $logged = null): void
    {
        if (!is_resource($this->fsock) || feof($this->fsock)) {
            $this->bitmap = 0;
            throw new ConnectionClosedException('Connection closed prematurely');
        }

        if (!isset($logged)) {
            $logged = $data;
        }

        switch ($this->compress) {
            case self::NET_SSH2_COMPRESSION_ZLIB_AT_OPENSSH:
                if (!$this->isAuthenticated()) {
                    break;
                }
                // fall-through
            case self::NET_SSH2_COMPRESSION_ZLIB:
                if (!$this->regenerate_compression_context) {
                    $header = '';
                } else {
                    $this->regenerate_compression_context = false;
                    $this->compress_context = deflate_init(ZLIB_ENCODING_RAW, ['window' => 15]);
                    $header = "\x78\x9C";
                }
                if ($this->compress_context) {
                    $data = $header . deflate_add($this->compress_context, $data, ZLIB_PARTIAL_FLUSH);
                }
        }

        // 4 (packet length) + 1 (padding length) + 4 (minimal padding amount) == 9
        $packet_length = strlen($data) + 9;
        if ($this->encrypt && $this->encrypt->usesNonce()) {
            $packet_length -= 4;
        }
        // round up to the nearest $this->encrypt_block_size
        $packet_length += (($this->encrypt_block_size - 1) * $packet_length) % $this->encrypt_block_size;
        // subtracting strlen($data) is obvious - subtracting 5 is necessary because of packet_length and padding_length
        $padding_length = $packet_length - strlen($data) - 5;
        switch (true) {
            case $this->encrypt && $this->encrypt->usesNonce():
            case $this->hmac_create instanceof Hash && $this->hmac_create_etm:
                $padding_length += 4;
                $packet_length += 4;
        }

        $padding = Random::string($padding_length);

        // we subtract 4 from packet_length because the packet_length field isn't supposed to include itself
        $packet = pack('NCa*', $packet_length - 4, $padding_length, $data . $padding);

        $hmac = '';
        if ($this->hmac_create instanceof Hash && !$this->hmac_create_etm) {
            if (($this->hmac_create->getHash() & "\xFF\xFF\xFF\xFF") == 'umac') {
                $this->hmac_create->setNonce("\0\0\0\0" . pack('N', $this->send_seq_no));
                $hmac = $this->hmac_create->hash($packet);
            } else {
                $hmac = $this->hmac_create->hash(pack('Na*', $this->send_seq_no, $packet));
            }
        }

        if ($this->encrypt) {
            switch ($this->encryptName) {
                case 'aes128-gcm@openssh.com':
                case 'aes256-gcm@openssh.com':
                    $this->encrypt->setNonce(
                        $this->encryptFixedPart .
                        $this->encryptInvocationCounter
                    );
                    Strings::increment_str($this->encryptInvocationCounter);
                    $this->encrypt->setAAD($temp = ($packet & "\xFF\xFF\xFF\xFF"));
                    $packet = $temp . $this->encrypt->encrypt(substr($packet, 4));
                    break;
                case 'chacha20-poly1305@openssh.com':
                    // This should be impossible, but we are checking anyway to narrow the type for Psalm.
                    if (!($this->encrypt instanceof ChaCha20)) {
                        throw new LogicException('$this->encrypt is not a ' . ChaCha20::class);
                    }

                    $nonce = pack('N2', 0, $this->send_seq_no);

                    $this->encrypt->setNonce($nonce);
                    $this->lengthEncrypt->setNonce($nonce);

                    $length = $this->lengthEncrypt->encrypt($packet & "\xFF\xFF\xFF\xFF");

                    $this->encrypt->setCounter(0);
                    // this is the same approach that's implemented in Salsa20::createPoly1305Key()
                    // but we don't want to use the same AEAD construction that RFC8439 describes
                    // for ChaCha20-Poly1305 so we won't rely on it (see Salsa20::poly1305())
                    $this->encrypt->setPoly1305Key(
                        $this->encrypt->encrypt(str_repeat("\0", 32))
                    );
                    $this->encrypt->setAAD($length);
                    $this->encrypt->setCounter(1);
                    $packet = $length . $this->encrypt->encrypt(substr($packet, 4));
                    break;
                default:
                    $packet = $this->hmac_create instanceof Hash && $this->hmac_create_etm ?
                        ($packet & "\xFF\xFF\xFF\xFF") . $this->encrypt->encrypt(substr($packet, 4)) :
                        $this->encrypt->encrypt($packet);
            }
        }

        if ($this->hmac_create instanceof Hash && $this->hmac_create_etm) {
            if (($this->hmac_create->getHash() & "\xFF\xFF\xFF\xFF") == 'umac') {
                $this->hmac_create->setNonce("\0\0\0\0" . pack('N', $this->send_seq_no));
                $hmac = $this->hmac_create->hash($packet);
            } else {
                $hmac = $this->hmac_create->hash(pack('Na*', $this->send_seq_no, $packet));
            }
        }

        $this->send_seq_no++;

        $packet .= $this->encrypt && $this->encrypt->usesNonce() ? $this->encrypt->getTag() : $hmac;

        $start = microtime(true);
        $sent = @fwrite($this->fsock, $packet);
        $stop = microtime(true);

        if (defined('NET_SSH2_LOGGING')) {
            $current = microtime(true);
            $message_number = sprintf(
                '-> %s (since last: %s, network: %ss)',
                ($constantName = MessageType::findConstantNameByValue($value = ord($logged[0]), false))
                    ? "SSH_MSG_$constantName"
                    : "UNKNOWN ($value)",
                round($current - $this->last_packet, 4),
                round($stop - $start, 4)
            );
            $this->append_log($message_number, $logged);
            $this->last_packet = $current;
        }

        if (strlen($packet) != $sent) {
            $this->bitmap = 0;
            $message = $sent === false ?
                'Unable to write ' . strlen($packet) . ' bytes' :
                "Only $sent of " . strlen($packet) . " bytes were sent";
            throw new RuntimeException($message);
        }
    }

    /**
     * Logs data packets
     *
     * Makes sure that only the last 1MB worth of packets will be logged
     */
    private function append_log(string $message_number, string $message): void
    {
        $this->append_log_helper(
            NET_SSH2_LOGGING,
            $message_number,
            $message,
            $this->message_number_log,
            $this->message_log,
            $this->log_size,
            $this->realtime_log_file,
            $this->realtime_log_wrap,
            $this->realtime_log_size
        );
    }

    /**
     * Logs data packet helper
     *
     * @param resource &$realtime_log_file
     */
    protected function append_log_helper(int $constant, string $message_number, string $message, array &$message_number_log, array &$message_log, int &$log_size, &$realtime_log_file, bool &$realtime_log_wrap, int &$realtime_log_size): void
    {
        // remove the byte identifying the message type from all but the first two messages (ie. the identification strings)
        if (strlen($message_number) > 2) {
            Strings::shift($message);
        }

        switch ($constant) {
            // useful for benchmarks
            case self::LOG_SIMPLE:
                $message_number_log[] = $message_number;
                break;
            case self::LOG_SIMPLE_REALTIME:
                echo $message_number;
                echo PHP_SAPI == 'cli' ? "\r\n" : '<br>';
                @flush();
                @ob_flush();
                break;
            // the most useful log for SSH2
            case self::LOG_COMPLEX:
                $message_number_log[] = $message_number;
                $log_size += strlen($message);
                $message_log[] = $message;
                while ($log_size > self::LOG_MAX_SIZE) {
                    $log_size -= strlen(array_shift($message_log));
                    array_shift($message_number_log);
                }
                break;
            // dump the output out realtime; packets may be interspersed with non packets,
            // passwords won't be filtered out and select other packets may not be correctly
            // identified
            case self::LOG_REALTIME:
                switch (PHP_SAPI) {
                    case 'cli':
                        $start = $stop = "\r\n";
                        break;
                    default:
                        $start = '<pre>';
                        $stop = '</pre>';
                }
                echo $start . $this->format_log([$message], [$message_number]) . $stop;
                @flush();
                @ob_flush();
                break;
            // basically the same thing as self::LOG_REALTIME with the caveat that NET_SSH2_LOG_REALTIME_FILENAME
            // needs to be defined and that the resultant log file will be capped out at self::LOG_MAX_SIZE.
            // the earliest part of the log file is denoted by the first <<< START >>> and is not going to necessarily
            // at the beginning of the file
            case self::LOG_REALTIME_FILE:
                if (!isset($realtime_log_file)) {
                    // PHP doesn't seem to like using constants in fopen()
                    $filename = NET_SSH2_LOG_REALTIME_FILENAME;
                    $fp = fopen($filename, 'w');
                    $realtime_log_file = $fp;
                }
                if (!is_resource($realtime_log_file)) {
                    break;
                }
                $entry = $this->format_log([$message], [$message_number]);
                if ($realtime_log_wrap) {
                    $temp = "<<< START >>>\r\n";
                    $entry .= $temp;
                    fseek($realtime_log_file, ftell($realtime_log_file) - strlen($temp));
                }
                $realtime_log_size += strlen($entry);
                if ($realtime_log_size > self::LOG_MAX_SIZE) {
                    fseek($realtime_log_file, 0);
                    $realtime_log_size = strlen($entry);
                    $realtime_log_wrap = true;
                }
                fwrite($realtime_log_file, $entry);
        }
    }

    /**
     * Sends channel data
     *
     * Spans multiple SSH_MSG_CHANNEL_DATAs if appropriate
     */
    protected function send_channel_packet(int $client_channel, string $data): void
    {
        while (strlen($data)) {
            if (!$this->window_size_client_to_server[$client_channel]) {
                $this->bitmap ^= self::MASK_WINDOW_ADJUST;
                // using an invalid channel will let the buffers be built up for the valid channels
                $this->get_channel_packet(-1);
                $this->bitmap ^= self::MASK_WINDOW_ADJUST;
            }

            /* The maximum amount of data allowed is determined by the maximum
               packet size for the channel, and the current window size, whichever
               is smaller.
                 -- http://tools.ietf.org/html/rfc4254#section-5.2 */
            $max_size = min(
                $this->packet_size_client_to_server[$client_channel],
                $this->window_size_client_to_server[$client_channel]
            );

            $temp = Strings::shift($data, $max_size);
            $packet = Strings::packSSH2(
                'CNs',
                MessageType::CHANNEL_DATA,
                $this->server_channels[$client_channel],
                $temp
            );
            $this->window_size_client_to_server[$client_channel] -= strlen($temp);
            $this->send_binary_packet($packet);
        }
    }

    /**
     * Closes and flushes a channel
     *
     * \phpseclib3\Net\SSH2 doesn't properly close most channels.  For exec() channels are normally closed by the server
     * and for SFTP channels are presumably closed when the client disconnects.  This functions is intended
     * for SCP more than anything.
     */
    private function close_channel(int $client_channel, bool $want_reply = false): void
    {
        // see http://tools.ietf.org/html/rfc4254#section-5.3

        $this->send_binary_packet(pack('CN', MessageType::CHANNEL_EOF, $this->server_channels[$client_channel]));

        if (!$want_reply) {
            $this->send_binary_packet(pack('CN', MessageType::CHANNEL_CLOSE, $this->server_channels[$client_channel]));
        }

        $this->channel_status[$client_channel] = MessageType::CHANNEL_CLOSE;
        $this->channelCount--;

        $this->curTimeout = 5;

        while (!is_bool($this->get_channel_packet($client_channel))) {
        }

        if ($want_reply) {
            $this->send_binary_packet(pack('CN', MessageType::CHANNEL_CLOSE, $this->server_channels[$client_channel]));
        }

        $this->close_channel_bitmap($client_channel);
    }

    /**
     * Maintains execution state bitmap in response to channel closure
     */
    private function close_channel_bitmap(int $client_channel): void
    {
        switch ($client_channel) {
            case self::CHANNEL_SHELL:
                // Shell status has been maintained in the bitmap for backwards
                //  compatibility sake, but can be removed going forward
                if ($this->bitmap & self::MASK_SHELL) {
                    $this->bitmap &= ~self::MASK_SHELL;
                }
                break;
        }
    }

    /**
     * Disconnect
     *
     * @return false
     */
    protected function disconnect_helper(int $reason): bool
    {
        if ($this->bitmap & self::MASK_CONNECTED) {
            $data = Strings::packSSH2('CNss', MessageType::DISCONNECT, $reason, '', '');
            try {
                $this->send_binary_packet($data);
            } catch (\Exception $e) {
            }
        }

        $this->bitmap = 0;
        if (is_resource($this->fsock) && get_resource_type($this->fsock) === 'stream') {
            fclose($this->fsock);
        }

        return false;
    }

    /**
     * Returns a log of the packets that have been sent and received.
     *
     * Returns a string if NET_SSH2_LOGGING == self::LOG_COMPLEX, an array if NET_SSH2_LOGGING == self::LOG_SIMPLE and false if !defined('NET_SSH2_LOGGING')
     *
     * @return array|false|string
     */
    public function getLog()
    {
        if (!defined('NET_SSH2_LOGGING')) {
            return false;
        }

        switch (NET_SSH2_LOGGING) {
            case self::LOG_SIMPLE:
                return $this->message_number_log;
            case self::LOG_COMPLEX:
                $log = $this->format_log($this->message_log, $this->message_number_log);
                return PHP_SAPI == 'cli' ? $log : '<pre>' . $log . '</pre>';
            default:
                return false;
        }
    }

    /**
     * Formats a log for printing
     */
    protected function format_log(array $message_log, array $message_number_log): string
    {
        $output = '';
        for ($i = 0; $i < count($message_log); $i++) {
            $output .= $message_number_log[$i] . "\r\n";
            $current_log = $message_log[$i];
            $j = 0;
            do {
                if (strlen($current_log)) {
                    $output .= str_pad(dechex($j), 7, '0', STR_PAD_LEFT) . '0  ';
                }
                $fragment = Strings::shift($current_log, $this->log_short_width);
                $hex = substr(preg_replace_callback('#.#s', fn ($matches) => $this->log_boundary . str_pad(dechex(ord($matches[0])), 2, '0', STR_PAD_LEFT), $fragment), strlen($this->log_boundary));
                // replace non ASCII printable characters with dots
                // http://en.wikipedia.org/wiki/ASCII#ASCII_printable_characters
                // also replace < with a . since < messes up the output on web browsers
                $raw = preg_replace('#[^\x20-\x7E]|<#', '.', $fragment);
                $output .= str_pad($hex, $this->log_long_width - $this->log_short_width, ' ') . $raw . "\r\n";
                $j++;
            } while (strlen($current_log));
            $output .= "\r\n";
        }

        return $output;
    }

    /**
     * Helper function for agent->on_channel_open()
     *
     * Used when channels are created to inform agent
     * of said channel opening. Must be called after
     * channel open confirmation received
     */
    private function on_channel_open(): void
    {
        if (isset($this->agent)) {
            $this->agent->registerChannelOpen($this);
        }
    }

    /**
     * Returns the first value of the intersection of two arrays or false if
     * the intersection is empty. The order is defined by the first parameter.
     *
     * @return mixed False if intersection is empty, else intersected value.
     */
    private static function array_intersect_first(array $array1, array $array2)
    {
        foreach ($array1 as $value) {
            if (in_array($value, $array2)) {
                return $value;
            }
        }
        return false;
    }

    /**
     * Returns all errors / debug messages on the SSH layer
     *
     * If you are looking for messages from the SFTP layer, please see SFTP::getSFTPErrors()
     *
     * @return string[]
     */
    public function getErrors(): array
    {
        return $this->errors;
    }

    /**
     * Returns the last error received on the SSH layer
     *
     * If you are looking for messages from the SFTP layer, please see SFTP::getLastSFTPError()
     */
    public function getLastError(): string
    {
        $count = count($this->errors);

        if ($count > 0) {
            return $this->errors[$count - 1];
        }
    }

    /**
     * Return the server identification.
     *
     * @return string|false
     */
    public function getServerIdentification()
    {
        $this->connect();

        return $this->server_identifier;
    }

    /**
     * Returns a list of algorithms the server supports
     */
    public function getServerAlgorithms(): array
    {
        $this->connect();

        return [
            'kex' => $this->kex_algorithms,
            'hostkey' => $this->server_host_key_algorithms,
            'client_to_server' => [
                'crypt' => $this->encryption_algorithms_client_to_server,
                'mac' => $this->mac_algorithms_client_to_server,
                'comp' => $this->compression_algorithms_client_to_server,
                'lang' => $this->languages_client_to_server,
            ],
            'server_to_client' => [
                'crypt' => $this->encryption_algorithms_server_to_client,
                'mac' => $this->mac_algorithms_server_to_client,
                'comp' => $this->compression_algorithms_server_to_client,
                'lang' => $this->languages_server_to_client,
            ],
        ];
    }

    /**
     * Returns a list of KEX algorithms that phpseclib supports
     */
    public static function getSupportedKEXAlgorithms(): array
    {
        $kex_algorithms = [
            // Elliptic Curve Diffie-Hellman Key Agreement (ECDH) using
            // Curve25519. See doc/curve25519-sha256@libssh.org.txt in the
            // libssh repository for more information.
            'curve25519-sha256',
            'curve25519-sha256@libssh.org',

            'ecdh-sha2-nistp256', // RFC 5656
            'ecdh-sha2-nistp384', // RFC 5656
            'ecdh-sha2-nistp521', // RFC 5656

            'diffie-hellman-group-exchange-sha256',// RFC 4419
            'diffie-hellman-group-exchange-sha1',  // RFC 4419

            // Diffie-Hellman Key Agreement (DH) using integer modulo prime
            // groups.
            'diffie-hellman-group14-sha256',
            'diffie-hellman-group14-sha1', // REQUIRED
            'diffie-hellman-group15-sha512',
            'diffie-hellman-group16-sha512',
            'diffie-hellman-group17-sha512',
            'diffie-hellman-group18-sha512',

            'diffie-hellman-group1-sha1', // REQUIRED
        ];

        return $kex_algorithms;
    }

    /**
     * Returns a list of host key algorithms that phpseclib supports
     */
    public static function getSupportedHostKeyAlgorithms(): array
    {
        return [
            'ssh-ed25519', // https://tools.ietf.org/html/draft-ietf-curdle-ssh-ed25519-02
            'ecdsa-sha2-nistp256', // RFC 5656
            'ecdsa-sha2-nistp384', // RFC 5656
            'ecdsa-sha2-nistp521', // RFC 5656
            'rsa-sha2-256', // RFC 8332
            'rsa-sha2-512', // RFC 8332
            'ssh-rsa', // RECOMMENDED  sign   Raw RSA Key
            'ssh-dss',  // REQUIRED     sign   Raw DSS Key
        ];
    }

    /**
     * Returns a list of symmetric key algorithms that phpseclib supports
     */
    public static function getSupportedEncryptionAlgorithms(): array
    {
        $algos = [
            // from <https://tools.ietf.org/html/rfc5647>:
            'aes128-gcm@openssh.com',
            'aes256-gcm@openssh.com',

            // from <http://tools.ietf.org/html/rfc4345#section-4>:
            'arcfour256',
            'arcfour128',

            //'arcfour',      // OPTIONAL          the ARCFOUR stream cipher with a 128-bit key

            // CTR modes from <http://tools.ietf.org/html/rfc4344#section-4>:
            'aes128-ctr',     // RECOMMENDED       AES (Rijndael) in SDCTR mode, with 128-bit key
            'aes192-ctr',     // RECOMMENDED       AES with 192-bit key
            'aes256-ctr',     // RECOMMENDED       AES with 256-bit key

            // from <https://github.com/openssh/openssh-portable/blob/001aa55/PROTOCOL.chacha20poly1305>:
            // one of the big benefits of chacha20-poly1305 is speed. the problem is...
            // libsodium doesn't generate the poly1305 keys in the way ssh does and openssl's PHP bindings don't even
            // seem to support poly1305 currently. so even if libsodium or openssl are being used for the chacha20
            // part, pure-PHP has to be used for the poly1305 part and that's gonna cause a big slow down.
            // speed-wise it winds up being faster to use AES (when openssl is available) and some HMAC
            // (which is always gonna be super fast to compute thanks to the hash extension, which
            // "is bundled and compiled into PHP by default")
            'chacha20-poly1305@openssh.com',

            'twofish128-ctr', // OPTIONAL          Twofish in SDCTR mode, with 128-bit key
            'twofish192-ctr', // OPTIONAL          Twofish with 192-bit key
            'twofish256-ctr', // OPTIONAL          Twofish with 256-bit key

            'aes128-cbc',     // RECOMMENDED       AES with a 128-bit key
            'aes192-cbc',     // OPTIONAL          AES with a 192-bit key
            'aes256-cbc',     // OPTIONAL          AES in CBC mode, with a 256-bit key

            'twofish128-cbc', // OPTIONAL          Twofish with a 128-bit key
            'twofish192-cbc', // OPTIONAL          Twofish with a 192-bit key
            'twofish256-cbc',
            'twofish-cbc',    // OPTIONAL          alias for "twofish256-cbc"
                              //                   (this is being retained for historical reasons)

            'blowfish-ctr',   // OPTIONAL          Blowfish in SDCTR mode

            'blowfish-cbc',   // OPTIONAL          Blowfish in CBC mode

            '3des-ctr',       // RECOMMENDED       Three-key 3DES in SDCTR mode

            '3des-cbc',       // REQUIRED          three-key 3DES in CBC mode

             //'none'           // OPTIONAL          no encryption; NOT RECOMMENDED
        ];

        if (self::$crypto_engine) {
            $engines = [self::$crypto_engine];
        } else {
            $engines = [
                'libsodium',
                'OpenSSL (GCM)',
                'OpenSSL',
                'Eval',
                'PHP',
            ];
        }

        $ciphers = [];

        foreach ($engines as $engine) {
            foreach ($algos as $algo) {
                $obj = self::encryption_algorithm_to_crypt_instance($algo);
                if ($obj instanceof Rijndael) {
                    $obj->setKeyLength((int) preg_replace('#[^\d]#', '', $algo));
                }
                switch ($algo) {
                    case 'chacha20-poly1305@openssh.com':
                    case 'arcfour128':
                    case 'arcfour256':
                        if ($engine != 'Eval') {
                            continue 2;
                        }
                        break;
                    case 'aes128-gcm@openssh.com':
                    case 'aes256-gcm@openssh.com':
                        if ($engine == 'OpenSSL') {
                            continue 2;
                        }
                        $obj->setNonce('dummydummydu');
                }
                if ($obj->isValidEngine($engine)) {
                    $algos = array_diff($algos, [$algo]);
                    $ciphers[] = $algo;
                }
            }
        }

        return $ciphers;
    }

    /**
     * Returns a list of MAC algorithms that phpseclib supports
     */
    public static function getSupportedMACAlgorithms(): array
    {
        return [
            'hmac-sha2-256-etm@openssh.com',
            'hmac-sha2-512-etm@openssh.com',
            'umac-64-etm@openssh.com',
            'umac-128-etm@openssh.com',
            'hmac-sha1-etm@openssh.com',

            // from <http://www.ietf.org/rfc/rfc6668.txt>:
            'hmac-sha2-256',// RECOMMENDED     HMAC-SHA256 (digest length = key length = 32)
            'hmac-sha2-512',// OPTIONAL        HMAC-SHA512 (digest length = key length = 64)

            // from <https://tools.ietf.org/html/draft-miller-secsh-umac-01>:
            'umac-64@openssh.com',
            'umac-128@openssh.com',

            'hmac-sha1-96', // RECOMMENDED     first 96 bits of HMAC-SHA1 (digest length = 12, key length = 20)
            'hmac-sha1',    // REQUIRED        HMAC-SHA1 (digest length = key length = 20)
            'hmac-md5-96',  // OPTIONAL        first 96 bits of HMAC-MD5 (digest length = 12, key length = 16)
            'hmac-md5',     // OPTIONAL        HMAC-MD5 (digest length = key length = 16)
            //'none'          // OPTIONAL        no MAC; NOT RECOMMENDED
        ];
    }

    /**
     * Returns a list of compression algorithms that phpseclib supports
     */
    public static function getSupportedCompressionAlgorithms(): array
    {
        $algos = ['none']; // REQUIRED        no compression
        if (function_exists('deflate_init')) {
            $algos[] = 'zlib@openssh.com'; // https://datatracker.ietf.org/doc/html/draft-miller-secsh-compression-delayed
            $algos[] = 'zlib';
        }
        return $algos;
    }

    /**
     * Return list of negotiated algorithms
     *
     * Uses the same format as https://www.php.net/ssh2-methods-negotiated
     */
    public function getAlgorithmsNegotiated(): array
    {
        $this->connect();

        $compression_map = [
            self::NET_SSH2_COMPRESSION_NONE => 'none',
            self::NET_SSH2_COMPRESSION_ZLIB => 'zlib',
            self::NET_SSH2_COMPRESSION_ZLIB_AT_OPENSSH => 'zlib@openssh.com',
        ];

        return [
            'kex' => $this->kex_algorithm,
            'hostkey' => $this->signature_format,
            'client_to_server' => [
                'crypt' => $this->encryptName,
                'mac' => $this->hmac_create_name,
                'comp' => $compression_map[$this->compress],
            ],
            'server_to_client' => [
                'crypt' => $this->decryptName,
                'mac' => $this->hmac_check_name,
                'comp' => $compression_map[$this->decompress],
            ],
        ];
    }

    /**
     * Force multiple channels (even if phpseclib has decided to disable them)
     */
    public function forceMultipleChannels(): void
    {
        $this->errorOnMultipleChannels = false;
    }

    /**
     * Allows you to set the terminal
     */
    public function setTerminal(string $term): void
    {
        $this->term = $term;
    }

    /**
     * Accepts an associative array with up to four parameters as described at
     * <https://www.php.net/manual/en/function.ssh2-connect.php>
     */
    public function setPreferredAlgorithms(array $methods): void
    {
        $preferred = $methods;

        if (isset($preferred['kex'])) {
            $preferred['kex'] = array_intersect(
                $preferred['kex'],
                static::getSupportedKEXAlgorithms()
            );
        }

        if (isset($preferred['hostkey'])) {
            $preferred['hostkey'] = array_intersect(
                $preferred['hostkey'],
                static::getSupportedHostKeyAlgorithms()
            );
        }

        $keys = ['client_to_server', 'server_to_client'];
        foreach ($keys as $key) {
            if (isset($preferred[$key])) {
                $a = &$preferred[$key];
                if (isset($a['crypt'])) {
                    $a['crypt'] = array_intersect(
                        $a['crypt'],
                        static::getSupportedEncryptionAlgorithms()
                    );
                }
                if (isset($a['comp'])) {
                    $a['comp'] = array_intersect(
                        $a['comp'],
                        static::getSupportedCompressionAlgorithms()
                    );
                }
                if (isset($a['mac'])) {
                    $a['mac'] = array_intersect(
                        $a['mac'],
                        static::getSupportedMACAlgorithms()
                    );
                }
            }
        }

        $keys = [
            'kex',
            'hostkey',
            'client_to_server/crypt',
            'client_to_server/comp',
            'client_to_server/mac',
            'server_to_client/crypt',
            'server_to_client/comp',
            'server_to_client/mac',
        ];
        foreach ($keys as $key) {
            $p = $preferred;
            $m = $methods;

            $subkeys = explode('/', $key);
            foreach ($subkeys as $subkey) {
                if (!isset($p[$subkey])) {
                    continue 2;
                }
                $p = $p[$subkey];
                $m = $m[$subkey];
            }

            if (count($p) != count($m)) {
                $diff = array_diff($m, $p);
                $msg = count($diff) == 1 ?
                    ' is not a supported algorithm' :
                    ' are not supported algorithms';
                throw new UnsupportedAlgorithmException(implode(', ', $diff) . $msg);
            }
        }

        $this->preferred = $preferred;
    }

    /**
     * Returns the banner message.
     *
     * Quoting from the RFC, "in some jurisdictions, sending a warning message before
     * authentication may be relevant for getting legal protection."
     */
    public function getBannerMessage(): string
    {
        return $this->banner_message;
    }

    /**
     * Returns the server public host key.
     *
     * Caching this the first time you connect to a server and checking the result on subsequent connections
     * is recommended.  Returns false if the server signature is not signed correctly with the public host key.
     *
     * @return string|false
     * @throws RuntimeException on badly formatted keys
     * @throws NoSupportedAlgorithmsException when the key isn't in a supported format
     */
    public function getServerPublicHostKey()
    {
        if (!($this->bitmap & self::MASK_CONSTRUCTOR)) {
            $this->connect();
        }

        $signature = $this->signature;
        $server_public_host_key = base64_encode($this->server_public_host_key);

        if ($this->signature_validated) {
            return $this->bitmap ?
                $this->signature_format . ' ' . $server_public_host_key :
                false;
        }

        $this->signature_validated = true;

        switch ($this->signature_format) {
            case 'ssh-ed25519':
            case 'ecdsa-sha2-nistp256':
            case 'ecdsa-sha2-nistp384':
            case 'ecdsa-sha2-nistp521':
                $key = EC::loadFormat('OpenSSH', $server_public_host_key)
                    ->withSignatureFormat('SSH2');
                switch ($this->signature_format) {
                    case 'ssh-ed25519':
                        $hash = 'sha512';
                        break;
                    case 'ecdsa-sha2-nistp256':
                        $hash = 'sha256';
                        break;
                    case 'ecdsa-sha2-nistp384':
                        $hash = 'sha384';
                        break;
                    case 'ecdsa-sha2-nistp521':
                        $hash = 'sha512';
                }
                $key = $key->withHash($hash);
                break;
            case 'ssh-dss':
                $key = DSA::loadFormat('OpenSSH', $server_public_host_key)
                    ->withSignatureFormat('SSH2')
                    ->withHash('sha1');
                break;
            case 'ssh-rsa':
            case 'rsa-sha2-256':
            case 'rsa-sha2-512':
                // could be ssh-rsa, rsa-sha2-256, rsa-sha2-512
                // we don't check here because we already checked in key_exchange
                // some signatures have the type embedded within the message and some don't
                [, $signature] = Strings::unpackSSH2('ss', $signature);

                $key = RSA::loadFormat('OpenSSH', $server_public_host_key)
                    ->withPadding(RSA::SIGNATURE_PKCS1);
                switch ($this->signature_format) {
                    case 'rsa-sha2-512':
                        $hash = 'sha512';
                        break;
                    case 'rsa-sha2-256':
                        $hash = 'sha256';
                        break;
                    //case 'ssh-rsa':
                    default:
                        $hash = 'sha1';
                }
                $key = $key->withHash($hash);
                break;
            default:
                $this->disconnect_helper(DisconnectReason::HOST_KEY_NOT_VERIFIABLE);
                throw new NoSupportedAlgorithmsException('Unsupported signature format');
        }

        if (!$key->verify($this->exchange_hash, $signature)) {
            return $this->disconnect_helper(DisconnectReason::HOST_KEY_NOT_VERIFIABLE);
        };

        return $this->signature_format . ' ' . $server_public_host_key;
    }

    /**
     * Returns the exit status of an SSH command or false.
     *
     * @return false|int
     */
    public function getExitStatus()
    {
        if (is_null($this->exit_status)) {
            return false;
        }
        return $this->exit_status;
    }

    /**
     * Returns the number of columns for the terminal window size.
     */
    public function getWindowColumns(): int
    {
        return $this->windowColumns;
    }

    /**
     * Returns the number of rows for the terminal window size.
     */
    public function getWindowRows(): int
    {
        return $this->windowRows;
    }

    /**
     * Sets the number of columns for the terminal window size.
     */
    public function setWindowColumns(int $value): void
    {
        $this->windowColumns = $value;
    }

    /**
     * Sets the number of rows for the terminal window size.
     */
    public function setWindowRows(int $value): void
    {
        $this->windowRows = $value;
    }

    /**
     * Sets the number of columns and rows for the terminal window size.
     */
    public function setWindowSize(int $columns = 80, int $rows = 24): void
    {
        $this->windowColumns = $columns;
        $this->windowRows = $rows;
    }

    /**
     * To String Magic Method
     *
     * @return string
     */
    #[\ReturnTypeWillChange]
    public function __toString()
    {
        return $this->getResourceId();
    }

    /**
     * Get Resource ID
     *
     * We use {} because that symbols should not be in URL according to
     * {@link http://tools.ietf.org/html/rfc3986#section-2 RFC}.
     * It will safe us from any conflicts, because otherwise regexp will
     * match all alphanumeric domains.
     */
    public function getResourceId(): string
    {
        return '{' . spl_object_hash($this) . '}';
    }

    public static function getConnectionByResourceId(string $id): SSH2|null
    {
        if (array_key_exists($id, self::$connections)) {
            /**
             * @psalm-ignore-var
             * @var SSH2|null $ssh2
             */
            $ssh2 =  self::$connections[$id]->get();
            return $ssh2;
        }
        return null;
    }

    /**
     * Return all excising connections
     *
     * @return array<string, SSH2>
     */
    public static function getConnections(): array
    {
        if (!class_exists('WeakReference')) {
            /** @var array<string, SSH2> */
            return self::$connections;
        }
        $temp = [];
        foreach (self::$connections as $key => $ref) {
            $temp[$key] = $ref->get();
        }
        return $temp;
    }

    /**
     * Update packet types in log history
     */
    private function updateLogHistory(string $old, string $new): void
    {
        if (defined('NET_SSH2_LOGGING') && NET_SSH2_LOGGING == self::LOG_COMPLEX) {
            $this->message_number_log[count($this->message_number_log) - 1] = str_replace(
                $old,
                $new,
                $this->message_number_log[count($this->message_number_log) - 1]
            );
        }
    }

    /**
     * Return the list of authentication methods that may productively continue authentication.
     *
     * @see https://tools.ietf.org/html/rfc4252#section-5.1
     */
    public function getAuthMethodsToContinue(): ?array
    {
        return $this->auth_methods_to_continue;
    }

    /**
     * Enables "smart" multi-factor authentication (MFA)
     */
    public function enableSmartMFA(): void
    {
        $this->smartMFA = true;
    }

    /**
     * Disables "smart" multi-factor authentication (MFA)
     */
    public function disableSmartMFA(): void
    {
        $this->smartMFA = false;
    }
}