/vendors/phpseclib/Net/SSH2.php

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<?php
set_include_path(get_include_path() . ':' . VENDORS . 'phpseclib');
/* vim: set expandtab tabstop=4 shiftwidth=4 softtabstop=4: */

/**
 * Pure-PHP implementation of SSHv2.
 *
 * PHP versions 4 and 5
 *
 * Here are some examples of how to use this library:
 * <code>
 * <?php
 *    include('Net/SSH2.php');
 *
 *    $ssh = new Net_SSH2('www.domain.tld');
 *    if (!$ssh->login('username', 'password')) {
 *        exit('Login Failed');
 *    }
 *
 *    echo $ssh->exec('pwd');
 *    echo $ssh->exec('ls -la');
 * ?>
 * </code>
 *
 * <code>
 * <?php
 *    include('Crypt/RSA.php');
 *    include('Net/SSH2.php');
 *
 *    $key = new Crypt_RSA();
 *    //$key->setPassword('whatever');
 *    $key->loadKey(file_get_contents('privatekey'));
 *
 *    $ssh = new Net_SSH2('www.domain.tld');
 *    if (!$ssh->login('username', $key)) {
 *        exit('Login Failed');
 *    }
 *
 *    echo $ssh->read('username@username:~$');
 *    $ssh->write("ls -la\n");
 *    echo $ssh->read('username@username:~$');
 * ?>
 * </code>
 *
 * LICENSE: Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 * 
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 * 
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 *
 * @category   Net
 * @package    Net_SSH2
 * @author     Jim Wigginton <terrafrost@php.net>
 * @copyright  MMVII Jim Wigginton
 * @license    http://www.opensource.org/licenses/mit-license.html  MIT License
 * @version    $Id: SSH2.php,v 1.53 2010-10-24 01:24:30 terrafrost Exp $
 * @link       http://phpseclib.sourceforge.net
 */

/**
 * Include Math_BigInteger
 *
 * Used to do Diffie-Hellman key exchange and DSA/RSA signature verification.
 */
if (!class_exists('Math_BigInteger')) {
    require_once('Math/BigInteger.php');
}

/**
 * Include Crypt_Random
 */
// the class_exists() will only be called if the crypt_random function hasn't been defined and
// will trigger a call to __autoload() if you're wanting to auto-load classes
// call function_exists() a second time to stop the require_once from being called outside
// of the auto loader
if (!function_exists('crypt_random') && !class_exists('Crypt_Random') && !function_exists('crypt_random')) {
    require_once('Crypt/Random.php');
}

/**
 * Include Crypt_Hash
 */
if (!class_exists('Crypt_Hash')) {
    require_once('Crypt/Hash.php');
}

/**
 * Include Crypt_TripleDES
 */
if (!class_exists('Crypt_TripleDES')) {
    require_once('Crypt/TripleDES.php');
}

/**
 * Include Crypt_RC4
 */
if (!class_exists('Crypt_RC4')) {
    require_once('Crypt/RC4.php');
}

/**
 * Include Crypt_AES
 */
if (!class_exists('Crypt_AES')) {
    require_once('Crypt/AES.php');
}

/**#@+
 * Execution Bitmap Masks
 *
 * @see Net_SSH2::bitmap
 * @access private
 */
define('NET_SSH2_MASK_CONSTRUCTOR', 0x00000001);
define('NET_SSH2_MASK_LOGIN',       0x00000002);
define('NET_SSH2_MASK_SHELL',       0x00000004);
/**#@-*/

/**#@+
 * 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
 * recepient 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 snipet:
 *     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 Net_SSH2::_send_channel_packet()
 * @see Net_SSH2::_get_channel_packet()
 * @access private
 */
define('NET_SSH2_CHANNEL_EXEC', 0); // PuTTy uses 0x100
define('NET_SSH2_CHANNEL_SHELL',1);
/**#@-*/

/**#@+
 * @access public
 * @see Net_SSH2::getLog()
 */
/**
 * Returns the message numbers
 */
define('NET_SSH2_LOG_SIMPLE',  1);
/**
 * Returns the message content
 */
define('NET_SSH2_LOG_COMPLEX', 2);
/**
 * Outputs the content real-time
 */
define('NET_SSH2_LOG_REALTIME', 3);
/**#@-*/

/**#@+
 * @access public
 * @see Net_SSH2::read()
 */
/**
 * Returns when a string matching $expect exactly is found
 */
define('NET_SSH2_READ_SIMPLE',  1);
/**
 * Returns when a string matching the regular expression $expect is found
 */
define('NET_SSH2_READ_REGEX', 2);
/**
 * Make sure that the log never gets larger than this
 */
define('NET_SSH2_LOG_MAX_SIZE', 1024 * 1024);
/**#@-*/

/**
 * Pure-PHP implementation of SSHv2.
 *
 * @author  Jim Wigginton <terrafrost@php.net>
 * @version 0.1.0
 * @access  public
 * @package Net_SSH2
 */
class Net_SSH2 {
    /**
     * The SSH identifier
     *
     * @var String
     * @access private
     */
    var $identifier = 'SSH-2.0-phpseclib_0.3';

    /**
     * The Socket Object
     *
     * @var Object
     * @access private
     */
    var $fsock;

    /**
     * Execution Bitmap
     *
     * The bits that are set reprsent 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.
     *
     * @var Integer
     * @access private
     */
    var $bitmap = 0;

    /**
     * Error information
     *
     * @see Net_SSH2::getErrors()
     * @see Net_SSH2::getLastError()
     * @var String
     * @access private
     */
    var $errors = array();

    /**
     * Server Identifier
     *
     * @see Net_SSH2::getServerIdentification()
     * @var String
     * @access private
     */
    var $server_identifier = '';

    /**
     * Key Exchange Algorithms
     *
     * @see Net_SSH2::getKexAlgorithims()
     * @var Array
     * @access private
     */
    var $kex_algorithms;

    /**
     * Server Host Key Algorithms
     *
     * @see Net_SSH2::getServerHostKeyAlgorithms()
     * @var Array
     * @access private
     */
    var $server_host_key_algorithms;

    /**
     * Encryption Algorithms: Client to Server
     *
     * @see Net_SSH2::getEncryptionAlgorithmsClient2Server()
     * @var Array
     * @access private
     */
    var $encryption_algorithms_client_to_server;

    /**
     * Encryption Algorithms: Server to Client
     *
     * @see Net_SSH2::getEncryptionAlgorithmsServer2Client()
     * @var Array
     * @access private
     */
    var $encryption_algorithms_server_to_client;

    /**
     * MAC Algorithms: Client to Server
     *
     * @see Net_SSH2::getMACAlgorithmsClient2Server()
     * @var Array
     * @access private
     */
    var $mac_algorithms_client_to_server;

    /**
     * MAC Algorithms: Server to Client
     *
     * @see Net_SSH2::getMACAlgorithmsServer2Client()
     * @var Array
     * @access private
     */
    var $mac_algorithms_server_to_client;

    /**
     * Compression Algorithms: Client to Server
     *
     * @see Net_SSH2::getCompressionAlgorithmsClient2Server()
     * @var Array
     * @access private
     */
    var $compression_algorithms_client_to_server;

    /**
     * Compression Algorithms: Server to Client
     *
     * @see Net_SSH2::getCompressionAlgorithmsServer2Client()
     * @var Array
     * @access private
     */
    var $compression_algorithms_server_to_client;

    /**
     * Languages: Server to Client
     *
     * @see Net_SSH2::getLanguagesServer2Client()
     * @var Array
     * @access private
     */
    var $languages_server_to_client;

    /**
     * Languages: Client to Server
     *
     * @see Net_SSH2::getLanguagesClient2Server()
     * @var Array
     * @access private
     */
    var $languages_client_to_server;

    /**
     * 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 Net_SSH2::Net_SSH2()
     * @see Net_SSH2::_send_binary_packet()
     * @var Integer
     * @access private
     */
    var $encrypt_block_size = 8;

    /**
     * Block Size for Client to Server Encryption
     *
     * @see Net_SSH2::Net_SSH2()
     * @see Net_SSH2::_get_binary_packet()
     * @var Integer
     * @access private
     */
    var $decrypt_block_size = 8;

    /**
     * Server to Client Encryption Object
     *
     * @see Net_SSH2::_get_binary_packet()
     * @var Object
     * @access private
     */
    var $decrypt = false;

    /**
     * Client to Server Encryption Object
     *
     * @see Net_SSH2::_send_binary_packet()
     * @var Object
     * @access private
     */
    var $encrypt = false;

    /**
     * Client to Server HMAC Object
     *
     * @see Net_SSH2::_send_binary_packet()
     * @var Object
     * @access private
     */
    var $hmac_create = false;

    /**
     * Server to Client HMAC Object
     *
     * @see Net_SSH2::_get_binary_packet()
     * @var Object
     * @access private
     */
    var $hmac_check = false;

    /**
     * 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 Net_SSH2::_get_binary_packet()
     * @var Integer
     * @access private
     */
    var $hmac_size = false;

    /**
     * Server Public Host Key
     *
     * @see Net_SSH2::getServerPublicHostKey()
     * @var String
     * @access private
     */
    var $server_public_host_key;

    /**
     * Session identifer
     *
     * "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 Net_SSH2::_key_exchange()
     * @var String
     * @access private
     */
    var $session_id = false;

    /**
     * Exchange hash
     *
     * The current exchange hash
     *
     * @see Net_SSH2::_key_exchange()
     * @var String
     * @access private
     */
    var $exchange_hash = false;

    /**
     * Message Numbers
     *
     * @see Net_SSH2::Net_SSH2()
     * @var Array
     * @access private
     */
    var $message_numbers = array();

    /**
     * Disconnection Message 'reason codes' defined in RFC4253
     *
     * @see Net_SSH2::Net_SSH2()
     * @var Array
     * @access private
     */
    var $disconnect_reasons = array();

    /**
     * SSH_MSG_CHANNEL_OPEN_FAILURE 'reason codes', defined in RFC4254
     *
     * @see Net_SSH2::Net_SSH2()
     * @var Array
     * @access private
     */
    var $channel_open_failure_reasons = array();

    /**
     * Terminal Modes
     *
     * @link http://tools.ietf.org/html/rfc4254#section-8
     * @see Net_SSH2::Net_SSH2()
     * @var Array
     * @access private
     */
    var $terminal_modes = array();

    /**
     * SSH_MSG_CHANNEL_EXTENDED_DATA's data_type_codes
     *
     * @link http://tools.ietf.org/html/rfc4254#section-5.2
     * @see Net_SSH2::Net_SSH2()
     * @var Array
     * @access private
     */
    var $channel_extended_data_type_codes = array();

    /**
     * Send Sequence Number
     *
     * See 'Section 6.4.  Data Integrity' of rfc4253 for more info.
     *
     * @see Net_SSH2::_send_binary_packet()
     * @var Integer
     * @access private
     */
    var $send_seq_no = 0;

    /**
     * Get Sequence Number
     *
     * See 'Section 6.4.  Data Integrity' of rfc4253 for more info.
     *
     * @see Net_SSH2::_get_binary_packet()
     * @var Integer
     * @access private
     */
    var $get_seq_no = 0;

    /**
     * Server Channels
     *
     * Maps client channels to server channels
     *
     * @see Net_SSH2::_get_channel_packet()
     * @see Net_SSH2::exec()
     * @var Array
     * @access private
     */
    var $server_channels = array();

    /**
     * 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 Net_SSH2::_get_channel_packet()
     * @see Net_SSH2::exec()
     * @var Array
     * @access private
     */
    var $channel_buffers = array();

    /**
     * Channel Status
     *
     * Contains the type of the last sent message
     *
     * @see Net_SSH2::_get_channel_packet()
     * @var Array
     * @access private
     */
    var $channel_status = array();

    /**
     * Packet Size
     *
     * Maximum packet size indexed by channel
     *
     * @see Net_SSH2::_send_channel_packet()
     * @var Array
     * @access private
     */
    var $packet_size_client_to_server = array();

    /**
     * Message Number Log
     *
     * @see Net_SSH2::getLog()
     * @var Array
     * @access private
     */
    var $message_number_log = array();

    /**
     * Message Log
     *
     * @see Net_SSH2::getLog()
     * @var Array
     * @access private
     */
    var $message_log = array();

    /**
     * The Window Size
     *
     * Bytes the other party can send before it must wait for the window to be adjusted (0x7FFFFFFF = 4GB)
     *
     * @var Integer
     * @see Net_SSH2::_send_channel_packet()
     * @see Net_SSH2::exec()
     * @access private
     */
    var $window_size = 0x7FFFFFFF;

    /**
     * Window size
     *
     * Window size indexed by channel
     *
     * @see Net_SSH2::_send_channel_packet()
     * @var Array
     * @access private
     */
    var $window_size_client_to_server = array();

    /**
     * Server signature
     *
     * Verified against $this->session_id
     *
     * @see Net_SSH2::getServerPublicHostKey()
     * @var String
     * @access private
     */
    var $signature = '';

    /**
     * Server signature format
     *
     * ssh-rsa or ssh-dss.
     *
     * @see Net_SSH2::getServerPublicHostKey()
     * @var String
     * @access private
     */
    var $signature_format = '';

    /**
     * Interactive Buffer
     *
     * @see Net_SSH2::read()
     * @var Array
     * @access private
     */
    var $interactiveBuffer = '';

    /**
     * Current log size
     *
     * Should never exceed NET_SSH2_LOG_MAX_SIZE
     *
     * @see Net_SSH2::_send_binary_packet()
     * @see Net_SSH2::_get_binary_packet()
     * @var Integer
     * @access private
     */
    var $log_size;

    /**
     * Timeout
     *
     * @see Net_SSH2::setTimeout()
     * @access private
     */
    var $timeout;

    /**
     * Current Timeout
     *
     * @see Net_SSH2::_get_channel_packet()
     * @access private
     */
    var $curTimeout;

    /**
     * Real-time log file pointer
     *
     * @see Net_SSH2::_append_log()
     * @access private
     */
    var $realtime_log_file;

    /**
     * Real-time log file size
     *
     * @see Net_SSH2::_append_log()
     * @access private
     */
    var $realtime_log_size;

    /**
     * Has the signature been validated?
     *
     * @see Net_SSH2::getServerPublicHostKey()
     * @access private
     */
    var $signature_validated = false;

    /**
     * Real-time log file wrap boolean
     *
     * @see Net_SSH2::_append_log()
     * @access private
     */
    var $realtime_log_wrap;

    /**
     * Default Constructor.
     *
     * Connects to an SSHv2 server
     *
     * @param String $host
     * @param optional Integer $port
     * @param optional Integer $timeout
     * @return Net_SSH2
     * @access public
     */
    function Net_SSH2($host, $port = 22, $timeout = 10)
    {
        $this->message_numbers = array(
            1 => 'NET_SSH2_MSG_DISCONNECT',
            2 => 'NET_SSH2_MSG_IGNORE',
            3 => 'NET_SSH2_MSG_UNIMPLEMENTED',
            4 => 'NET_SSH2_MSG_DEBUG',
            5 => 'NET_SSH2_MSG_SERVICE_REQUEST',
            6 => 'NET_SSH2_MSG_SERVICE_ACCEPT',
            20 => 'NET_SSH2_MSG_KEXINIT',
            21 => 'NET_SSH2_MSG_NEWKEYS',
            30 => 'NET_SSH2_MSG_KEXDH_INIT',
            31 => 'NET_SSH2_MSG_KEXDH_REPLY',
            50 => 'NET_SSH2_MSG_USERAUTH_REQUEST',
            51 => 'NET_SSH2_MSG_USERAUTH_FAILURE',
            52 => 'NET_SSH2_MSG_USERAUTH_SUCCESS',
            53 => 'NET_SSH2_MSG_USERAUTH_BANNER',

            80 => 'NET_SSH2_MSG_GLOBAL_REQUEST',
            81 => 'NET_SSH2_MSG_REQUEST_SUCCESS',
            82 => 'NET_SSH2_MSG_REQUEST_FAILURE',
            90 => 'NET_SSH2_MSG_CHANNEL_OPEN',
            91 => 'NET_SSH2_MSG_CHANNEL_OPEN_CONFIRMATION',
            92 => 'NET_SSH2_MSG_CHANNEL_OPEN_FAILURE',
            93 => 'NET_SSH2_MSG_CHANNEL_WINDOW_ADJUST',
            94 => 'NET_SSH2_MSG_CHANNEL_DATA',
            95 => 'NET_SSH2_MSG_CHANNEL_EXTENDED_DATA',
            96 => 'NET_SSH2_MSG_CHANNEL_EOF',
            97 => 'NET_SSH2_MSG_CHANNEL_CLOSE',
            98 => 'NET_SSH2_MSG_CHANNEL_REQUEST',
            99 => 'NET_SSH2_MSG_CHANNEL_SUCCESS',
            100 => 'NET_SSH2_MSG_CHANNEL_FAILURE'
        );
        $this->disconnect_reasons = array(
            1 => 'NET_SSH2_DISCONNECT_HOST_NOT_ALLOWED_TO_CONNECT',
            2 => 'NET_SSH2_DISCONNECT_PROTOCOL_ERROR',
            3 => 'NET_SSH2_DISCONNECT_KEY_EXCHANGE_FAILED',
            4 => 'NET_SSH2_DISCONNECT_RESERVED',
            5 => 'NET_SSH2_DISCONNECT_MAC_ERROR',
            6 => 'NET_SSH2_DISCONNECT_COMPRESSION_ERROR',
            7 => 'NET_SSH2_DISCONNECT_SERVICE_NOT_AVAILABLE',
            8 => 'NET_SSH2_DISCONNECT_PROTOCOL_VERSION_NOT_SUPPORTED',
            9 => 'NET_SSH2_DISCONNECT_HOST_KEY_NOT_VERIFIABLE',
            10 => 'NET_SSH2_DISCONNECT_CONNECTION_LOST',
            11 => 'NET_SSH2_DISCONNECT_BY_APPLICATION',
            12 => 'NET_SSH2_DISCONNECT_TOO_MANY_CONNECTIONS',
            13 => 'NET_SSH2_DISCONNECT_AUTH_CANCELLED_BY_USER',
            14 => 'NET_SSH2_DISCONNECT_NO_MORE_AUTH_METHODS_AVAILABLE',
            15 => 'NET_SSH2_DISCONNECT_ILLEGAL_USER_NAME'
        );
        $this->channel_open_failure_reasons = array(
            1 => 'NET_SSH2_OPEN_ADMINISTRATIVELY_PROHIBITED'
        );
        $this->terminal_modes = array(
            0 => 'NET_SSH2_TTY_OP_END'
        );
        $this->channel_extended_data_type_codes = array(
            1 => 'NET_SSH2_EXTENDED_DATA_STDERR'
        );

        $this->_define_array(
            $this->message_numbers,
            $this->disconnect_reasons,
            $this->channel_open_failure_reasons,
            $this->terminal_modes,
            $this->channel_extended_data_type_codes,
            array(60 => 'NET_SSH2_MSG_USERAUTH_PASSWD_CHANGEREQ'),
            array(60 => 'NET_SSH2_MSG_USERAUTH_PK_OK'),
            array(60 => 'NET_SSH2_MSG_USERAUTH_INFO_REQUEST',
                  61 => 'NET_SSH2_MSG_USERAUTH_INFO_RESPONSE')
        );

        $start = strtok(microtime(), ' ') + strtok(''); // http://php.net/microtime#61838
        $this->fsock = @fsockopen($host, $port, $errno, $errstr, $timeout);
        if (!$this->fsock) {
            user_error(rtrim("Cannot connect to $host. Error $errno. $errstr"), E_USER_NOTICE);
            return;
        }
        $elapsed = strtok(microtime(), ' ') + strtok('') - $start;

        if ($timeout - $elapsed <= 0) {
            user_error(rtrim("Cannot connect to $host. Timeout error"), E_USER_NOTICE);
            return;
        }

        $read = array($this->fsock);
        $write = $except = NULL;

        stream_set_blocking($this->fsock, false);

        // on windows this returns a "Warning: Invalid CRT parameters detected" error
        if (!@stream_select($read, $write, $except, $timeout - $elapsed)) {
            user_error(rtrim("Cannot connect to $host. Banner timeout"), E_USER_NOTICE);
            return;
        }

        stream_set_blocking($this->fsock, true);

        /* 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." */
        $temp = '';
        $extra = '';
        while (!feof($this->fsock) && !preg_match('#^SSH-(\d\.\d+)#', $temp, $matches)) {
            if (substr($temp, -2) == "\r\n") {
                $extra.= $temp;
                $temp = '';
            }
            $temp.= fgets($this->fsock, 255);
        }

        if (feof($this->fsock)) {
            user_error('Connection closed by server', E_USER_NOTICE);
            return false;
        }

        $ext = array();
        if (extension_loaded('mcrypt')) {
            $ext[] = 'mcrypt';
        }
        if (extension_loaded('gmp')) {
            $ext[] = 'gmp';
        } else if (extension_loaded('bcmath')) {
            $ext[] = 'bcmath';
        }

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

        if (defined('NET_SSH2_LOGGING')) {
            $this->message_number_log[] = '<-';
            $this->message_number_log[] = '->';

            if (NET_SSH2_LOGGING == NET_SSH2_LOG_COMPLEX) {
                $this->message_log[] = $temp;
                $this->message_log[] = $this->identifier . "\r\n";
            }
        }

        $this->server_identifier = trim($temp, "\r\n");
        if (!empty($extra)) {
            $this->errors[] = utf8_decode($extra);
        }

        if ($matches[1] != '1.99' && $matches[1] != '2.0') {
            user_error("Cannot connect to SSH $matches[1] servers", E_USER_NOTICE);
            return;
        }

        fputs($this->fsock, $this->identifier . "\r\n");

        $response = $this->_get_binary_packet();
        if ($response === false) {
            user_error('Connection closed by server', E_USER_NOTICE);
            return;
        }

        if (ord($response[0]) != NET_SSH2_MSG_KEXINIT) {
            user_error('Expected SSH_MSG_KEXINIT', E_USER_NOTICE);
            return;
        }

        if (!$this->_key_exchange($response)) {
            return;
        }

        $this->bitmap = NET_SSH2_MASK_CONSTRUCTOR;
    }

    /**
     * Key Exchange
     *
     * @param String $kexinit_payload_server
     * @access private
     */
    function _key_exchange($kexinit_payload_server)
    {
        static $kex_algorithms = array(
            'diffie-hellman-group1-sha1', // REQUIRED
            'diffie-hellman-group14-sha1' // REQUIRED
        );

        static $server_host_key_algorithms = array(
            'ssh-rsa', // RECOMMENDED  sign   Raw RSA Key
            'ssh-dss'  // REQUIRED     sign   Raw DSS Key
        );

        static $encryption_algorithms = array(
            // from <http://tools.ietf.org/html/rfc4345#section-4>:
            'arcfour256',
            'arcfour128',

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

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

            '3des-cbc',   // REQUIRED          three-key 3DES in CBC mode
            'none'        // OPTIONAL          no encryption; NOT RECOMMENDED
        );

        static $mac_algorithms = array(
            '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
        );

        static $compression_algorithms = array(
            'none'   // REQUIRED        no compression
            //'zlib' // OPTIONAL        ZLIB (LZ77) compression
        );

        static $str_kex_algorithms, $str_server_host_key_algorithms,
               $encryption_algorithms_server_to_client, $mac_algorithms_server_to_client, $compression_algorithms_server_to_client,
               $encryption_algorithms_client_to_server, $mac_algorithms_client_to_server, $compression_algorithms_client_to_server;

        if (empty($str_kex_algorithms)) {
            $str_kex_algorithms = implode(',', $kex_algorithms);
            $str_server_host_key_algorithms = implode(',', $server_host_key_algorithms);
            $encryption_algorithms_server_to_client = $encryption_algorithms_client_to_server = implode(',', $encryption_algorithms);
            $mac_algorithms_server_to_client = $mac_algorithms_client_to_server = implode(',', $mac_algorithms);
            $compression_algorithms_server_to_client = $compression_algorithms_client_to_server = implode(',', $compression_algorithms);
        }

        $client_cookie = '';
        for ($i = 0; $i < 16; $i++) {
            $client_cookie.= chr(crypt_random(0, 255));
        }

        $response = $kexinit_payload_server;
        $this->_string_shift($response, 1); // skip past the message number (it should be SSH_MSG_KEXINIT)
        $server_cookie = $this->_string_shift($response, 16);

        $temp = unpack('Nlength', $this->_string_shift($response, 4));
        $this->kex_algorithms = explode(',', $this->_string_shift($response, $temp['length']));

        $temp = unpack('Nlength', $this->_string_shift($response, 4));
        $this->server_host_key_algorithms = explode(',', $this->_string_shift($response, $temp['length']));

        $temp = unpack('Nlength', $this->_string_shift($response, 4));
        $this->encryption_algorithms_client_to_server = explode(',', $this->_string_shift($response, $temp['length']));

        $temp = unpack('Nlength', $this->_string_shift($response, 4));
        $this->encryption_algorithms_server_to_client = explode(',', $this->_string_shift($response, $temp['length']));

        $temp = unpack('Nlength', $this->_string_shift($response, 4));
        $this->mac_algorithms_client_to_server = explode(',', $this->_string_shift($response, $temp['length']));

        $temp = unpack('Nlength', $this->_string_shift($response, 4));
        $this->mac_algorithms_server_to_client = explode(',', $this->_string_shift($response, $temp['length']));

        $temp = unpack('Nlength', $this->_string_shift($response, 4));
        $this->compression_algorithms_client_to_server = explode(',', $this->_string_shift($response, $temp['length']));

        $temp = unpack('Nlength', $this->_string_shift($response, 4));
        $this->compression_algorithms_server_to_client = explode(',', $this->_string_shift($response, $temp['length']));

        $temp = unpack('Nlength', $this->_string_shift($response, 4));
        $this->languages_client_to_server = explode(',', $this->_string_shift($response, $temp['length']));

        $temp = unpack('Nlength', $this->_string_shift($response, 4));
        $this->languages_server_to_client = explode(',', $this->_string_shift($response, $temp['length']));

        extract(unpack('Cfirst_kex_packet_follows', $this->_string_shift($response, 1)));
        $first_kex_packet_follows = $first_kex_packet_follows != 0;

        // the sending of SSH2_MSG_KEXINIT could go in one of two places.  this is the second place.
        $kexinit_payload_client = pack('Ca*Na*Na*Na*Na*Na*Na*Na*Na*Na*Na*CN',
            NET_SSH2_MSG_KEXINIT, $client_cookie, strlen($str_kex_algorithms), $str_kex_algorithms,
            strlen($str_server_host_key_algorithms), $str_server_host_key_algorithms, strlen($encryption_algorithms_client_to_server),
            $encryption_algorithms_client_to_server, strlen($encryption_algorithms_server_to_client), $encryption_algorithms_server_to_client,
            strlen($mac_algorithms_client_to_server), $mac_algorithms_client_to_server, strlen($mac_algorithms_server_to_client),
            $mac_algorithms_server_to_client, strlen($compression_algorithms_client_to_server), $compression_algorithms_client_to_server,
            strlen($compression_algorithms_server_to_client), $compression_algorithms_server_to_client, 0, '', 0, '',
            0, 0
        );

        if (!$this->_send_binary_packet($kexinit_payload_client)) {
            return false;
        }
        // here ends the second place.

        // we need to decide upon the symmetric encryption algorithms before we do the diffie-hellman key exchange
        for ($i = 0; $i < count($encryption_algorithms) && !in_array($encryption_algorithms[$i], $this->encryption_algorithms_server_to_client); $i++);
        if ($i == count($encryption_algorithms)) {
            user_error('No compatible server to client encryption algorithms found', E_USER_NOTICE);
            return $this->_disconnect(NET_SSH2_DISCONNECT_KEY_EXCHANGE_FAILED);
        }

        // 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 = $encryption_algorithms[$i];
        switch ($decrypt) {
            case '3des-cbc':
            case '3des-ctr':
                $decryptKeyLength = 24; // eg. 192 / 8
                break;
            case 'aes256-cbc':
            case 'aes256-ctr':
                $decryptKeyLength = 32; // eg. 256 / 8
                break;
            case 'aes192-cbc':
            case 'aes192-ctr':
                $decryptKeyLength = 24; // eg. 192 / 8
                break;
            case 'aes128-cbc':
            case 'aes128-ctr':
                $decryptKeyLength = 16; // eg. 128 / 8
                break;
            case 'arcfour':
            case 'arcfour128':
                $decryptKeyLength = 16; // eg. 128 / 8
                break;
            case 'arcfour256':
                $decryptKeyLength = 32; // eg. 128 / 8
                break;
            case 'none';
                $decryptKeyLength = 0;
        }

        for ($i = 0; $i < count($encryption_algorithms) && !in_array($encryption_algorithms[$i], $this->encryption_algorithms_client_to_server); $i++);
        if ($i == count($encryption_algorithms)) {
            user_error('No compatible client to server encryption algorithms found', E_USER_NOTICE);
            return $this->_disconnect(NET_SSH2_DISCONNECT_KEY_EXCHANGE_FAILED);
        }

        $encrypt = $encryption_algorithms[$i];
        switch ($encrypt) {
            case '3des-cbc':
            case '3des-ctr':
                $encryptKeyLength = 24;
                break;
            case 'aes256-cbc':
            case 'aes256-ctr':
                $encryptKeyLength = 32;
                break;
            case 'aes192-cbc':
            case 'aes192-ctr':
                $encryptKeyLength = 24;
                break;
            case 'aes128-cbc':
            case 'aes128-ctr':
                $encryptKeyLength = 16;
                break;
            case 'arcfour':
            case 'arcfour128':
                $encryptKeyLength = 16;
                break;
            case 'arcfour256':
                $encryptKeyLength = 32;
                break;
            case 'none';
                $encryptKeyLength = 0;
        }

        $keyLength = $decryptKeyLength > $encryptKeyLength ? $decryptKeyLength : $encryptKeyLength;

        // through diffie-hellman key exchange a symmetric key is obtained
        for ($i = 0; $i < count($kex_algorithms) && !in_array($kex_algorithms[$i], $this->kex_algorithms); $i++);
        if ($i == count($kex_algorithms)) {
            user_error('No compatible key exchange algorithms found', E_USER_NOTICE);
            return $this->_disconnect(NET_SSH2_DISCONNECT_KEY_EXCHANGE_FAILED);
        }

        switch ($kex_algorithms[$i]) {
            // see http://tools.ietf.org/html/rfc2409#section-6.2 and 
            // http://tools.ietf.org/html/rfc2412, appendex E
            case 'diffie-hellman-group1-sha1':
                $p = pack('H256', 'FFFFFFFFFFFFFFFFC90FDAA22168C234C4C6628B80DC1CD129024E088A67CC74' . 
                                  '020BBEA63B139B22514A08798E3404DDEF9519B3CD3A431B302B0A6DF25F1437' . 
                                  '4FE1356D6D51C245E485B576625E7EC6F44C42E9A637ED6B0BFF5CB6F406B7ED' . 
                                  'EE386BFB5A899FA5AE9F24117C4B1FE649286651ECE65381FFFFFFFFFFFFFFFF');
                $keyLength = $keyLength < 160 ? $keyLength : 160;
                $hash = 'sha1';
                break;
            // see http://tools.ietf.org/html/rfc3526#section-3
            case 'diffie-hellman-group14-sha1':
                $p = pack('H512', 'FFFFFFFFFFFFFFFFC90FDAA22168C234C4C6628B80DC1CD129024E088A67CC74' . 
                                  '020BBEA63B139B22514A08798E3404DDEF9519B3CD3A431B302B0A6DF25F1437' . 
                                  '4FE1356D6D51C245E485B576625E7EC6F44C42E9A637ED6B0BFF5CB6F406B7ED' . 
                                  'EE386BFB5A899FA5AE9F24117C4B1FE649286651ECE45B3DC2007CB8A163BF05' . 
                                  '98DA48361C55D39A69163FA8FD24CF5F83655D23DCA3AD961C62F356208552BB' . 
                                  '9ED529077096966D670C354E4ABC9804F1746C08CA18217C32905E462E36CE3B' . 
                                  'E39E772C180E86039B2783A2EC07A28FB5C55DF06F4C52C9DE2BCBF695581718' . 
                                  '3995497CEA956AE515D2261898FA051015728E5A8AACAA68FFFFFFFFFFFFFFFF');
                $keyLength = $keyLength < 160 ? $keyLength : 160;
                $hash = 'sha1';
        }

        $p = new Math_BigInteger($p, 256);
        //$q = $p->bitwise_rightShift(1);

        /* To increase the speed of the key exchange, both client and server may
           reduce the size of their private exponents.  It should be at least
           twice as long as the key material that is generated from the shared
           secret.  For more details, see the paper by van Oorschot and Wiener
           [VAN-OORSCHOT].

           -- http://tools.ietf.org/html/rfc4419#section-6.2 */
        $q = new Math_BigInteger(1);
        $q = $q->bitwise_leftShift(2 * $keyLength);
        $q = $q->subtract(new Math_BigInteger(1));

        $g = new Math_BigInteger(2);
        $x = new Math_BigInteger();
        $x->setRandomGenerator('crypt_random');
        $x = $x->random(new Math_BigInteger(1), $q);
        $e = $g->modPow($x, $p);

        $eBytes = $e->toBytes(true);
        $data = pack('CNa*', NET_SSH2_MSG_KEXDH_INIT, strlen($eBytes), $eBytes);

        if (!$this->_send_binary_packet($data)) {
            user_error('Connection closed by server', E_USER_NOTICE);
            return false;
        }

        $response = $this->_get_binary_packet();
        if ($response === false) {
            user_error('Connection closed by server', E_USER_NOTICE);
            return false;
        }
        extract(unpack('Ctype', $this->_string_shift($response, 1)));

        if ($type != NET_SSH2_MSG_KEXDH_REPLY) {
            user_error('Expected SSH_MSG_KEXDH_REPLY', E_USER_NOTICE);
            return false;
        }

        $temp = unpack('Nlength', $this->_string_shift($response, 4));
        $this->server_public_host_key = $server_public_host_key = $this->_string_shift($response, $temp['length']);

        $temp = unpack('Nlength', $this->_string_shift($server_public_host_key, 4));
        $public_key_format = $this->_string_shift($server_public_host_key, $temp['length']);

        $temp = unpack('Nlength', $this->_string_shift($response, 4));
        $fBytes = $this->_string_shift($response, $temp['length']);
        $f = new Math_BigInteger($fBytes, -256);

        $temp = unpack('Nlength', $this->_string_shift($response, 4));
        $this->signature = $this->_string_shift($response, $temp['length']);

        $temp = unpack('Nlength', $this->_string_shift($this->signature, 4));
        $this->signature_format = $this->_string_shift($this->signature, $temp['length']);

        $key = $f->modPow($x, $p);
        $keyBytes = $key->toBytes(true);

        $this->exchange_hash = pack('Na*Na*Na*Na*Na*Na*Na*Na*',
            strlen($this->identifier), $this->identifier, strlen($this->server_identifier), $this->server_identifier,
            strlen($kexinit_payload_client), $kexinit_payload_client, strlen($kexinit_payload_server),
            $kexinit_payload_server, strlen($this->server_public_host_key), $this->server_public_host_key, strlen($eBytes),
            $eBytes, strlen($fBytes), $fBytes, strlen($keyBytes), $keyBytes
        );

        $this->exchange_hash = pack('H*', $hash($this->exchange_hash));

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

        for ($i = 0; $i < count($server_host_key_algorithms) && !in_array($server_host_key_algorithms[$i], $this->server_host_key_algorithms); $i++);
        if ($i == count($server_host_key_algorithms)) {
            user_error('No compatible server host key algorithms found', E_USER_NOTICE);
            return $this->_disconnect(NET_SSH2_DISCONNECT_KEY_EXCHANGE_FAILED);
        }

        if ($public_key_format != $server_host_key_algorithms[$i] || $this->signature_format != $server_host_key_algorithms[$i]) {
            user_error('Sever Host Key Algorithm Mismatch', E_USER_NOTICE);
            return $this->_disconnect(NET_SSH2_DISCONNECT_KEY_EXCHANGE_FAILED);
        }

        $packet = pack('C',
            NET_SSH2_MSG_NEWKEYS
        );

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

        $response = $this->_get_binary_packet();

        if ($response === false) {
            user_error('Connection closed by server', E_USER_NOTICE);
            return false;
        }

        extract(unpack('Ctype', $this->_string_shift($response, 1)));

        if ($type != NET_SSH2_MSG_NEWKEYS) {
            user_error('Expected SSH_MSG_NEWKEYS', E_USER_NOTICE);
            return false;
        }

        switch ($encrypt) {
            case '3des-cbc':
                $this->encrypt = new Crypt_TripleDES();
                // $this->encrypt_block_size = 64 / 8 == the default
                break;
            case '3des-ctr':
                $this->encrypt = new Crypt_TripleDES(CRYPT_DES_MODE_CTR);
                // $this->encrypt_block_size = 64 / 8 == the default
                break;
            case 'aes256-cbc':
            case 'aes192-cbc':
            case 'aes128-cbc':
                $this->encrypt = new Crypt_AES();
                $this->encrypt_block_size = 16; // eg. 128 / 8
                break;
            case 'aes256-ctr':
            case 'aes192-ctr':
            case 'aes128-ctr':
                $this->encrypt = new Crypt_AES(CRYPT_AES_MODE_CTR);
                $this->encrypt_block_size = 16; // eg. 128 / 8
                break;
            case 'arcfour':
            case 'arcfour128':
            case 'arcfour256':
                $this->encrypt = new Crypt_RC4();
                break;
            case 'none';
                //$this->encrypt = new Crypt_Null();
        }

        switch ($decrypt) {
            case '3des-cbc':
                $this->decrypt = new Crypt_TripleDES();
                break;
            case '3des-ctr':
                $this->decrypt = new Crypt_TripleDES(CRYPT_DES_MODE_CTR);
                break;
            case 'aes256-cbc':
            case 'aes192-cbc':
            case 'aes128-cbc':
                $this->decrypt = new Crypt_AES();
                $this->decrypt_block_size = 16;
                break;
            case 'aes256-ctr':
            case 'aes192-ctr':
            case 'aes128-ctr':
                $this->decrypt = new Crypt_AES(CRYPT_AES_MODE_CTR);
                $this->decrypt_block_size = 16;
                break;
            case 'arcfour':
            case 'arcfour128':
            case 'arcfour256':
                $this->decrypt = new Crypt_RC4();
                break;
            case 'none';
                //$this->decrypt = new Crypt_Null();
        }

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

        if ($this->encrypt) {
            $this->encrypt->enableContinuousBuffer();
            $this->encrypt->disablePadding();

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

            $key = pack('H*', $hash($keyBytes . $this->exchange_hash . 'C' . $this->session_id));
            while ($encryptKeyLength > strlen($key)) {
                $key.= pack('H*', $hash($keyBytes . $this->exchange_hash . $key));
            }
            $this->encrypt->setKey(substr($key, 0, $encryptKeyLength));
        }

        if ($this->decrypt) {
            $this->decrypt->enableContinuousBuffer();
            $this->decrypt->disablePadding();

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

            $key = pack('H*', $hash($keyBytes . $this->exchange_hash . 'D' . $this->session_id));
            while ($decryptKeyLength > strlen($key)) {
                $key.= pack('H*', $hash($keyBytes . $this->exchange_hash . $key));
            }
            $this->decrypt->setKey(substr($key, 0, $decryptKeyLength));
        }

        /* 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));
        }

        for ($i = 0; $i < count($mac_algorithms) && !in_array($mac_algorithms[$i], $this->mac_algorithms_client_to_server); $i++);
        if ($i == count($mac_algorithms)) {
            user_error('No compatible client to server message authentication algorithms found', E_USER_NOTICE);
            return $this->_disconnect(NET_SSH2_DISCONNECT_KEY_EXCHANGE_FAILED);
        }

        $createKeyLength = 0; // ie. $mac_algorithms[$i] == 'none'
        switch ($mac_algorithms[$i]) {
            case 'hmac-sha1':
                $this->hmac_create = new Crypt_Hash('sha1');
                $createKeyLength = 20;
                break;
            case 'hmac-sha1-96':
                $this->hmac_create = new Crypt_Hash('sha1-96');
                $createKeyLength = 20;
                break;
            case 'hmac-md5':
                $this->hmac_create = new Crypt_Hash('md5');
                $createKeyLength = 16;
                break;
            case 'hmac-md5-96':
                $this->hmac_create = new Crypt_Hash('md5-96');
                $createKeyLength = 16;
        }

        for ($i = 0; $i < count($mac_algorithms) && !in_array($mac_algorithms[$i], $this->mac_algorithms_server_to_client); $i++);
        if ($i == count($mac_algorithms)) {
            user_error('No compatible server to client message authentication algorithms found', E_USER_NOTICE);
            return $this->_disconnect(NET_SSH2_DISCONNECT_KEY_EXCHANGE_FAILED);
        }

        $checkKeyLength = 0;
        $this->hmac_size = 0;
        switch ($mac_algorithms[$i]) {
            case 'hmac-sha1':
                $this->hmac_check = new Crypt_Hash('sha1');
                $checkKeyLength = 20;
                $this->hmac_size = 20;
                break;
            case 'hmac-sha1-96':
                $this->hmac_check = new Crypt_Hash('sha1-96');
                $checkKeyLength = 20;
                $this->hmac_size = 12;
                break;
            case 'hmac-md5':
                $this->hmac_check = new Crypt_Hash('md5');
                $checkKeyLength = 16;
                $this->hmac_size = 16;
                break;
            case 'hmac-md5-96':
                $this->hmac_check = new Crypt_Hash('md5-96');
                $checkKeyLength = 16;
                $this->hmac_size = 12;
        }

        $key = pack('H*', $hash($keyBytes . $this->exchange_hash . 'E' . $this->session_id));
        while ($createKeyLength > strlen($key)) {
            $key.= pack('H*', $hash($keyBytes . $this->exchange_hash . $key));
        }
        $this->hmac_create->setKey(substr($key, 0, $createKeyLength));

        $key = pack('H*', $hash($keyBytes . $this->exchange_hash . 'F' . $this->session_id));
        while ($checkKeyLength > strlen($key)) {
            $key.= pack('H*', $hash($keyBytes . $this->exchange_hash . $key));
        }
        $this->hmac_check->setKey(substr($key, 0, $checkKeyLength));

        for ($i = 0; $i < count($compression_algorithms) && !in_array($compression_algorithms[$i], $this->compression_algorithms_server_to_client); $i++);
        if ($i == count($compression_algorithms)) {
            user_error('No compatible server to client compression algorithms found', E_USER_NOTICE);
            return $this->_disconnect(NET_SSH2_DISCONNECT_KEY_EXCHANGE_FAILED);
        }
        $this->decompress = $compression_algorithms[$i] == 'zlib';

        for ($i = 0; $i < count($compression_algorithms) && !in_array($compression_algorithms[$i], $this->compression_algorithms_client_to_server); $i++);
        if ($i == count($compression_algorithms)) {
            user_error('No compatible client to server compression algorithms found', E_USER_NOTICE);
            return $this->_disconnect(NET_SSH2_DISCONNECT_KEY_EXCHANGE_FAILED);
        }
        $this->compress = $compression_algorithms[$i] == 'zlib';

        return true;
    }

    /**
     * Login
     *
     * The $password parameter can be a plaintext password or a Crypt_RSA object.
     *
     * @param String $username
     * @param optional String $password
     * @return Boolean
     * @access public
     * @internal It might be worthwhile, at some point, to protect against {@link http://tools.ietf.org/html/rfc4251#section-9.3.9 traffic analysis}
     *           by sending dummy SSH_MSG_IGNORE messages.
     */
    function login($username, $password = '')
    {
        if (!($this->bitmap & NET_SSH2_MASK_CONSTRUCTOR)) {
            return false;
        }

        $packet = pack('CNa*',
            NET_SSH2_MSG_SERVICE_REQUEST, strlen('ssh-userauth'), 'ssh-userauth'
        );

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

        $response = $this->_get_binary_packet();
        if ($response === false) {
            user_error('Connection closed by server', E_USER_NOTICE);
            return false;
        }

        extract(unpack('Ctype', $this->_string_shift($response, 1)));

        if ($type != NET_SSH2_MSG_SERVICE_ACCEPT) {
            user_error('Expected SSH_MSG_SERVICE_ACCEPT', E_USER_NOTICE);
            return false;
        }

        // although PHP5's get_class() preserves the case, PHP4's does not
        if (is_object($password) && strtolower(get_class($password)) == 'crypt_rsa') {
            return $this->_privatekey_login($username, $password);
        }

        $packet = pack('CNa*Na*Na*CNa*',
            NET_SSH2_MSG_USERAUTH_REQUEST, strlen($username), $username, strlen('ssh-connection'), 'ssh-connection',
            strlen('password'), 'password', 0, strlen($password), $password
        );

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

        // remove the username and password from the last logged packet
        if (defined('NET_SSH2_LOGGING') && NET_SSH2_LOGGING == NET_SSH2_LOG_COMPLEX) {
            $packet = pack('CNa*Na*Na*CNa*',
                NET_SSH2_MSG_USERAUTH_REQUEST, strlen('username'), 'us…

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