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<?php

/**

 * CodeIgniter

 *

 * An open source application development framework for PHP

 *

 * This content is released under the MIT License (MIT)

 *

 * Copyright (c) 2014 - 2016, British Columbia Institute of Technology

 *

 * 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.

 *

 * @package	CodeIgniter

 * @author	EllisLab Dev Team

 * @copyright	Copyright (c) 2008 - 2014, EllisLab, Inc. (https://ellislab.com/)

 * @copyright	Copyright (c) 2014 - 2016, British Columbia Institute of Technology (http://bcit.ca/)

 * @license	http://opensource.org/licenses/MIT	MIT License

 * @link	https://codeigniter.com

 * @since	Version 3.0.0

 * @filesource

 */

defined('BASEPATH') OR exit('No direct script access allowed');

/**

 * CodeIgniter Encryption Class

 *

 * Provides two-way keyed encryption via PHP's MCrypt and/or OpenSSL extensions.

 *

 * @package		CodeIgniter

 * @subpackage	Libraries

 * @category	Libraries

 * @author		Andrey Andreev

 * @link		https://codeigniter.com/user_guide/libraries/encryption.html

 */

class CI_Encryption {

	/**

	 * Encryption cipher

	 *

	 * @var	string

	 */

	protected $_cipher = 'aes-128';

	/**

	 * Cipher mode

	 *

	 * @var	string

	 */

	protected $_mode = 'cbc';

	/**

	 * Cipher handle

	 *

	 * @var	mixed

	 */

	protected $_handle;

	/**

	 * Encryption key

	 *

	 * @var	string

	 */

	protected $_key;

	/**

	 * PHP extension to be used

	 *

	 * @var	string

	 */

	protected $_driver;

	/**

	 * List of usable drivers (PHP extensions)

	 *

	 * @var	array

	 */

	protected $_drivers = array();

	/**

	 * List of available modes

	 *

	 * @var	array

	 */

	protected $_modes = array(

		'mcrypt' => array(

			'cbc' => 'cbc',

			'ecb' => 'ecb',

			'ofb' => 'nofb',

			'ofb8' => 'ofb',

			'cfb' => 'ncfb',

			'cfb8' => 'cfb',

			'ctr' => 'ctr',

			'stream' => 'stream'

		),

		'openssl' => array(

			'cbc' => 'cbc',

			'ecb' => 'ecb',

			'ofb' => 'ofb',

			'cfb' => 'cfb',

			'cfb8' => 'cfb8',

			'ctr' => 'ctr',

			'stream' => '',

			'xts' => 'xts'

		)

	);

	/**

	 * List of supported HMAC algorithms

	 *

	 * name => digest size pairs

	 *

	 * @var	array

	 */

	protected $_digests = array(

		'sha224' => 28,

		'sha256' => 32,

		'sha384' => 48,

		'sha512' => 64

	);

	/**

	 * mbstring.func_override flag

	 *

	 * @var	bool

	 */

	protected static $func_override;

	// --------------------------------------------------------------------

	/**

	 * Class constructor

	 *

	 * @param	array	$params	Configuration parameters

	 * @return	void

	 */

	public function __construct(array $params = array())

	{

		$this->_drivers = array(

			'mcrypt' => defined('MCRYPT_DEV_URANDOM'),

			// While OpenSSL is available for PHP 5.3.0, an IV parameter

			// for the encrypt/decrypt functions is only available since 5.3.3

			'openssl' => (is_php('5.3.3') && extension_loaded('openssl'))

		);

		if ( ! $this->_drivers['mcrypt'] && ! $this->_drivers['openssl'])

		{

			show_error('Encryption: Unable to find an available encryption driver.');

		}

		isset(self::$func_override) OR self::$func_override = (extension_loaded('mbstring') && ini_get('mbstring.func_override'));

		$this->initialize($params);

		if ( ! isset($this->_key) && self::strlen($key = config_item('encryption_key')) > 0)

		{

			$this->_key = $key;

		}

		log_message('info', 'Encryption Class Initialized');

	}

	// --------------------------------------------------------------------

	/**

	 * Initialize

	 *

	 * @param	array	$params	Configuration parameters

	 * @return	CI_Encryption

	 */

	public function initialize(array $params)

	{

		if ( ! empty($params['driver']))

		{

			if (isset($this->_drivers[$params['driver']]))

			{

				if ($this->_drivers[$params['driver']])

				{

					$this->_driver = $params['driver'];

				}

				else

				{

					log_message('error', "Encryption: Driver '".$params['driver']."' is not available.");

				}

			}

			else

			{

				log_message('error', "Encryption: Unknown driver '".$params['driver']."' cannot be configured.");

			}

		}

		if (empty($this->_driver))

		{

			$this->_driver = ($this->_drivers['openssl'] === TRUE)

				? 'openssl'

				: 'mcrypt';

			log_message('debug', "Encryption: Auto-configured driver '".$this->_driver."'.");

		}

		empty($params['cipher']) && $params['cipher'] = $this->_cipher;

		empty($params['key']) OR $this->_key = $params['key'];

		$this->{'_'.$this->_driver.'_initialize'}($params);

		return $this;

	}

	// --------------------------------------------------------------------

	/**

	 * Initialize MCrypt

	 *

	 * @param	array	$params	Configuration parameters

	 * @return	void

	 */

	protected function _mcrypt_initialize($params)

	{

		if ( ! empty($params['cipher']))

		{

			$params['cipher'] = strtolower($params['cipher']);

			$this->_cipher_alias($params['cipher']);

			if ( ! in_array($params['cipher'], mcrypt_list_algorithms(), TRUE))

			{

				log_message('error', 'Encryption: MCrypt cipher '.strtoupper($params['cipher']).' is not available.');

			}

			else

			{

				$this->_cipher = $params['cipher'];

			}

		}

		if ( ! empty($params['mode']))

		{

			$params['mode'] = strtolower($params['mode']);

			if ( ! isset($this->_modes['mcrypt'][$params['mode']]))

			{

				log_message('error', 'Encryption: MCrypt mode '.strtoupper($params['mode']).' is not available.');

			}

			else

			{

				$this->_mode = $this->_modes['mcrypt'][$params['mode']];

			}

		}

		if (isset($this->_cipher, $this->_mode))

		{

			if (is_resource($this->_handle)

				&& (strtolower(mcrypt_enc_get_algorithms_name($this->_handle)) !== $this->_cipher

					OR strtolower(mcrypt_enc_get_modes_name($this->_handle)) !== $this->_mode)

			)

			{

				mcrypt_module_close($this->_handle);

			}

			if ($this->_handle = mcrypt_module_open($this->_cipher, '', $this->_mode, ''))

			{

				log_message('info', 'Encryption: MCrypt cipher '.strtoupper($this->_cipher).' initialized in '.strtoupper($this->_mode).' mode.');

			}

			else

			{

				log_message('error', 'Encryption: Unable to initialize MCrypt with cipher '.strtoupper($this->_cipher).' in '.strtoupper($this->_mode).' mode.');

			}

		}

	}

	// --------------------------------------------------------------------

	/**

	 * Initialize OpenSSL

	 *

	 * @param	array	$params	Configuration parameters

	 * @return	void

	 */

	protected function _openssl_initialize($params)

	{

		if ( ! empty($params['cipher']))

		{

			$params['cipher'] = strtolower($params['cipher']);

			$this->_cipher_alias($params['cipher']);

			$this->_cipher = $params['cipher'];

		}

		if ( ! empty($params['mode']))

		{

			$params['mode'] = strtolower($params['mode']);

			if ( ! isset($this->_modes['openssl'][$params['mode']]))

			{

				log_message('error', 'Encryption: OpenSSL mode '.strtoupper($params['mode']).' is not available.');

			}

			else

			{

				$this->_mode = $this->_modes['openssl'][$params['mode']];

			}

		}

		if (isset($this->_cipher, $this->_mode))

		{

			// This is mostly for the stream mode, which doesn't get suffixed in OpenSSL

			$handle = empty($this->_mode)

				? $this->_cipher

				: $this->_cipher.'-'.$this->_mode;

			if ( ! in_array($handle, openssl_get_cipher_methods(), TRUE))

			{

				$this->_handle = NULL;

				log_message('error', 'Encryption: Unable to initialize OpenSSL with method '.strtoupper($handle).'.');

			}

			else

			{

				$this->_handle = $handle;

				log_message('info', 'Encryption: OpenSSL initialized with method '.strtoupper($handle).'.');

			}

		}

	}

	// --------------------------------------------------------------------

	/**

	 * Create a random key

	 *

	 * @param	int	$length	Output length

	 * @return	string

	 */

	public function create_key($length)

	{

		if (function_exists('random_bytes'))

		{

			try

			{

				return random_bytes((int) $length);

			}

			catch (Exception $e)

			{

				log_message('error', $e->getMessage());

				return FALSE;

			}

		}

		elseif (defined('MCRYPT_DEV_URANDOM'))

		{

			return mcrypt_create_iv($length, MCRYPT_DEV_URANDOM);

		}

		$is_secure = NULL;

		$key = openssl_random_pseudo_bytes($length, $is_secure);

		return ($is_secure === TRUE)

			? $key

			: FALSE;

	}

	// --------------------------------------------------------------------

	/**

	 * Encrypt

	 *

	 * @param	string	$data	Input data

	 * @param	array	$params	Input parameters

	 * @return	string

	 */

	public function encrypt($data, array $params = NULL)

	{

		if (($params = $this->_get_params($params)) === FALSE)

		{

			return FALSE;

		}

		isset($params['key']) OR $params['key'] = $this->hkdf($this->_key, 'sha512', NULL, self::strlen($this->_key), 'encryption');

		if (($data = $this->{'_'.$this->_driver.'_encrypt'}($data, $params)) === FALSE)

		{

			return FALSE;

		}

		$params['base64'] && $data = base64_encode($data);

		if (isset($params['hmac_digest']))

		{

			isset($params['hmac_key']) OR $params['hmac_key'] = $this->hkdf($this->_key, 'sha512', NULL, NULL, 'authentication');

			return hash_hmac($params['hmac_digest'], $data, $params['hmac_key'], ! $params['base64']).$data;

		}

		return $data;

	}

	// --------------------------------------------------------------------

	/**

	 * Encrypt via MCrypt

	 *

	 * @param	string	$data	Input data

	 * @param	array	$params	Input parameters

	 * @return	string

	 */

	protected function _mcrypt_encrypt($data, $params)

	{

		if ( ! is_resource($params['handle']))

		{

			return FALSE;

		}

		// The greater-than-1 comparison is mostly a work-around for a bug,

		// where 1 is returned for ARCFour instead of 0.

		$iv = (($iv_size = mcrypt_enc_get_iv_size($params['handle'])) > 1)

			? $this->create_key($iv_size)

			: NULL;

		if (mcrypt_generic_init($params['handle'], $params['key'], $iv) < 0)

		{

			if ($params['handle'] !== $this->_handle)

			{

				mcrypt_module_close($params['handle']);

			}

			return FALSE;

		}

		// Use PKCS#7 padding in order to ensure compatibility with OpenSSL

		// and other implementations outside of PHP.

		if (in_array(strtolower(mcrypt_enc_get_modes_name($params['handle'])), array('cbc', 'ecb'), TRUE))

		{

			$block_size = mcrypt_enc_get_block_size($params['handle']);

			$pad = $block_size - (self::strlen($data) % $block_size);

			$data .= str_repeat(chr($pad), $pad);

		}

		// Work-around for yet another strange behavior in MCrypt.

		//

		// When encrypting in ECB mode, the IV is ignored. Yet

		// mcrypt_enc_get_iv_size() returns a value larger than 0

		// even if ECB is used AND mcrypt_generic_init() complains

		// if you don't pass an IV with length equal to the said

		// return value.

		//

		// This probably would've been fine (even though still wasteful),

		// but OpenSSL isn't that dumb and we need to make the process

		// portable, so ...

		$data = (mcrypt_enc_get_modes_name($params['handle']) !== 'ECB')

			? $iv.mcrypt_generic($params['handle'], $data)

			: mcrypt_generic($params['handle'], $data);

		mcrypt_generic_deinit($params['handle']);

		if ($params['handle'] !== $this->_handle)

		{

			mcrypt_module_close($params['handle']);

		}

		return $data;

	}

	// --------------------------------------------------------------------

	/**

	 * Encrypt via OpenSSL

	 *

	 * @param	string	$data	Input data

	 * @param	array	$params	Input parameters

	 * @return	string

	 */

	protected function _openssl_encrypt($data, $params)

	{

		if (empty($params['handle']))

		{

			return FALSE;

		}

		$iv = ($iv_size = openssl_cipher_iv_length($params['handle']))

			? $this->create_key($iv_size)

			: NULL;

		$data = openssl_encrypt(

			$data,

			$params['handle'],

			$params['key'],

			1, // DO NOT TOUCH!

			$iv

		);

		if ($data === FALSE)

		{

			return FALSE;

		}

		return $iv.$data;

	}

	// --------------------------------------------------------------------

	/**

	 * Decrypt

	 *

	 * @param	string	$data	Encrypted data

	 * @param	array	$params	Input parameters

	 * @return	string

	 */

	public function decrypt($data, array $params = NULL)

	{

		if (($params = $this->_get_params($params)) === FALSE)

		{

			return FALSE;

		}

		if (isset($params['hmac_digest']))

		{

			// This might look illogical, but it is done during encryption as well ...

			// The 'base64' value is effectively an inverted "raw data" parameter

			$digest_size = ($params['base64'])

				? $this->_digests[$params['hmac_digest']] * 2

				: $this->_digests[$params['hmac_digest']];

			if (self::strlen($data) <= $digest_size)

			{

				return FALSE;

			}

			$hmac_input = self::substr($data, 0, $digest_size);

			$data = self::substr($data, $digest_size);

			isset($params['hmac_key']) OR $params['hmac_key'] = $this->hkdf($this->_key, 'sha512', NULL, NULL, 'authentication');

			$hmac_check = hash_hmac($params['hmac_digest'], $data, $params['hmac_key'], ! $params['base64']);

			// Time-attack-safe comparison

			$diff = 0;

			for ($i = 0; $i < $digest_size; $i++)

			{

				$diff |= ord($hmac_input[$i]) ^ ord($hmac_check[$i]);

			}

			if ($diff !== 0)

			{

				return FALSE;

			}

		}

		if ($params['base64'])

		{

			$data = base64_decode($data);

		}

		isset($params['key']) OR $params['key'] = $this->hkdf($this->_key, 'sha512', NULL, self::strlen($this->_key), 'encryption');

		return $this->{'_'.$this->_driver.'_decrypt'}($data, $params);

	}

	// --------------------------------------------------------------------

	/**

	 * Decrypt via MCrypt

	 *

	 * @param	string	$data	Encrypted data

	 * @param	array	$params	Input parameters

	 * @return	string

	 */

	protected function _mcrypt_decrypt($data, $params)

	{

		if ( ! is_resource($params['handle']))

		{

			return FALSE;

		}

		// The greater-than-1 comparison is mostly a work-around for a bug,

		// where 1 is returned for ARCFour instead of 0.

		if (($iv_size = mcrypt_enc_get_iv_size($params['handle'])) > 1)

		{

			if (mcrypt_enc_get_modes_name($params['handle']) !== 'ECB')

			{

				$iv = self::substr($data, 0, $iv_size);

				$data = self::substr($data, $iv_size);

			}

			else

			{

				// MCrypt is dumb and this is ignored, only size matters

				$iv = str_repeat("\x0", $iv_size);

			}

		}

		else

		{

			$iv = NULL;

		}

		if (mcrypt_generic_init($params['handle'], $params['key'], $iv) < 0)

		{

			if ($params['handle'] !== $this->_handle)

			{

				mcrypt_module_close($params['handle']);

			}

			return FALSE;

		}

		$data = mdecrypt_generic($params['handle'], $data);

		// Remove PKCS#7 padding, if necessary

		if (in_array(strtolower(mcrypt_enc_get_modes_name($params['handle'])), array('cbc', 'ecb'), TRUE))

		{

			$data = self::substr($data, 0, -ord($data[self::strlen($data)-1]));

		}

		mcrypt_generic_deinit($params['handle']);

		if ($params['handle'] !== $this->_handle)

		{

			mcrypt_module_close($params['handle']);

		}

		return $data;

	}

	// --------------------------------------------------------------------

	/**

	 * Decrypt via OpenSSL

	 *

	 * @param	string	$data	Encrypted data

	 * @param	array	$params	Input parameters

	 * @return	string

	 */

	protected function _openssl_decrypt($data, $params)

	{

		if ($iv_size = openssl_cipher_iv_length($params['handle']))

		{

			$iv = self::substr($data, 0, $iv_size);

			$data = self::substr($data, $iv_size);

		}

		else

		{

			$iv = NULL;

		}

		return empty($params['handle'])

			? FALSE

			: openssl_decrypt(

				$data,

				$params['handle'],

				$params['key'],

				1, // DO NOT TOUCH!

				$iv

			);

	}

	// --------------------------------------------------------------------

	/**

	 * Get params

	 *

	 * @param	array	$params	Input parameters

	 * @return	array

	 */

	protected function _get_params($params)

	{

		if (empty($params))

		{

			return isset($this->_cipher, $this->_mode, $this->_key, $this->_handle)

				? array(

					'handle' => $this->_handle,

					'cipher' => $this->_cipher,

					'mode' => $this->_mode,

					'key' => NULL,

					'base64' => TRUE,

					'hmac_digest' => 'sha512',

					'hmac_key' => NULL

				)

				: FALSE;

		}

		elseif ( ! isset($params['cipher'], $params['mode'], $params['key']))

		{

			return FALSE;

		}

		if (isset($params['mode']))

		{

			$params['mode'] = strtolower($params['mode']);

			if ( ! isset($this->_modes[$this->_driver][$params['mode']]))

			{

				return FALSE;

			}

			else

			{

				$params['mode'] = $this->_modes[$this->_driver][$params['mode']];

			}

		}

		if (isset($params['hmac']) && $params['hmac'] === FALSE)

		{

			$params['hmac_digest'] = $params['hmac_key'] = NULL;

		}

		else

		{

			if ( ! isset($params['hmac_key']))

			{

				return FALSE;

			}

			elseif (isset($params['hmac_digest']))

			{

				$params['hmac_digest'] = strtolower($params['hmac_digest']);

				if ( ! isset($this->_digests[$params['hmac_digest']]))

				{

					return FALSE;

				}

			}

			else

			{

				$params['hmac_digest'] = 'sha512';

			}

		}

		$params = array(

			'handle' => NULL,

			'cipher' => $params['cipher'],

			'mode' => $params['mode'],

			'key' => $params['key'],

			'base64' => isset($params['raw_data']) ? ! $params['raw_data'] : FALSE,

			'hmac_digest' => $params['hmac_digest'],

			'hmac_key' => $params['hmac_key']

		);

		$this->_cipher_alias($params['cipher']);

		$params['handle'] = ($params['cipher'] !== $this->_cipher OR $params['mode'] !== $this->_mode)

			? $this->{'_'.$this->_driver.'_get_handle'}($params['cipher'], $params['mode'])

			: $this->_handle;

		return $params;

	}

	// --------------------------------------------------------------------

	/**

	 * Get MCrypt handle

	 *

	 * @param	string	$cipher	Cipher name

	 * @param	string	$mode	Encryption mode

	 * @return	resource

	 */

	protected function _mcrypt_get_handle($cipher, $mode)

	{

		return mcrypt_module_open($cipher, '', $mode, '');

	}

	// --------------------------------------------------------------------

	/**

	 * Get OpenSSL handle

	 *

	 * @param	string	$cipher	Cipher name

	 * @param	string	$mode	Encryption mode

	 * @return	string

	 */

	protected function _openssl_get_handle($cipher, $mode)

	{

		// OpenSSL methods aren't suffixed with '-stream' for this mode

		return ($mode === 'stream')

			? $cipher

			: $cipher.'-'.$mode;

	}

	// --------------------------------------------------------------------

	/**

	 * Cipher alias

	 *

	 * Tries to translate cipher names between MCrypt and OpenSSL's "dialects".

	 *

	 * @param	string	$cipher	Cipher name

	 * @return	void

	 */

	protected function _cipher_alias(&$cipher)

	{

		static $dictionary;

		if (empty($dictionary))

		{

			$dictionary = array(

				'mcrypt' => array(

					'aes-128' => 'rijndael-128',

					'aes-192' => 'rijndael-128',

					'aes-256' => 'rijndael-128',

					'des3-ede3' => 'tripledes',

					'bf' => 'blowfish',

					'cast5' => 'cast-128',

					'rc4' => 'arcfour',

					'rc4-40' => 'arcfour'

				),

				'openssl' => array(

					'rijndael-128' => 'aes-128',

					'tripledes' => 'des-ede3',

					'blowfish' => 'bf',

					'cast-128' => 'cast5',

					'arcfour' => 'rc4-40',

					'rc4' => 'rc4-40'

				)

			);

			// Notes:

			//

			// - Rijndael-128 is, at the same time all three of AES-128,

			//   AES-192 and AES-256. The only difference between them is

			//   the key size. Rijndael-192, Rijndael-256 on the other hand

			//   also have different block sizes and are NOT AES-compatible.

			//

			// - Blowfish is said to be supporting key sizes between

			//   4 and 56 bytes, but it appears that between MCrypt and

			//   OpenSSL, only those of 16 and more bytes are compatible.

			//   Also, don't know what MCrypt's 'blowfish-compat' is.

			//

			// - CAST-128/CAST5 produces a longer cipher when encrypted via

			//   OpenSSL, but (strangely enough) can be decrypted by either

			//   extension anyway.

			//   Also, it appears that OpenSSL uses 16 rounds regardless of

			//   the key size, while RFC2144 says that for key sizes lower

			//   than 11 bytes, only 12 rounds should be used. This makes

			//   it portable only with keys of between 11 and 16 bytes.

			//

			// - RC4 (ARCFour) has a strange implementation under OpenSSL.

			//   Its 'rc4-40' cipher method seems to work flawlessly, yet

			//   there's another one, 'rc4' that only works with a 16-byte key.

			//

			// - DES is compatible, but doesn't need an alias.

			//

			// Other seemingly matching ciphers between MCrypt, OpenSSL:

			//

			// - RC2 is NOT compatible and only an obscure forum post

			//   confirms that it is MCrypt's fault.

		}

		if (isset($dictionary[$this->_driver][$cipher]))

		{

			$cipher = $dictionary[$this->_driver][$cipher];

		}

	}

	// --------------------------------------------------------------------

	/**

	 * HKDF

	 *

	 * @link	https://tools.ietf.org/rfc/rfc5869.txt

	 * @param	$key	Input key

	 * @param	$digest	A SHA-2 hashing algorithm

	 * @param	$salt	Optional salt

	 * @param	$length	Output length (defaults to the selected digest size)

	 * @param	$info	Optional context/application-specific info

	 * @return	string	A pseudo-random key

	 */

	public function hkdf($key, $digest = 'sha512', $salt = NULL, $length = NULL, $info = '')

	{

		if ( ! isset($this->_digests[$digest]))

		{

			return FALSE;

		}

		if (empty($length) OR ! is_int($length))

		{

			$length = $this->_digests[$digest];

		}

		elseif ($length > (255 * $this->_digests[$digest]))

		{

			return FALSE;

		}

		self::strlen($salt) OR $salt = str_repeat("\0", $this->_digests[$digest]);

		$prk = hash_hmac($digest, $key, $salt, TRUE);

		$key = '';

		for ($key_block = '', $block_index = 1; self::strlen($key) < $length; $block_index++)

		{

			$key_block = hash_hmac($digest, $key_block.$info.chr($block_index), $prk, TRUE);

			$key .= $key_block;

		}

		return self::substr($key, 0, $length);

	}

	// --------------------------------------------------------------------

	/**

	 * __get() magic

	 *

	 * @param	string	$key	Property name

	 * @return	mixed

	 */

	public function __get($key)

	{

		// Because aliases

		if ($key === 'mode')

		{

			return array_search($this->_mode, $this->_modes[$this->_driver], TRUE);

		}

		elseif (in_array($key, array('cipher', 'driver', 'drivers', 'digests'), TRUE))

		{

			return $this->{'_'.$key};

		}

		return NULL;

	}

	// --------------------------------------------------------------------

	/**

	 * Byte-safe strlen()

	 *

	 * @param	string	$str

	 * @return	integer

	 */

	protected static function strlen($str)

	{

		return (self::$func_override)

			? mb_strlen($str, '8bit')

			: strlen($str);

	}

	// --------------------------------------------------------------------

	/**

	 * Byte-safe substr()

	 *

	 * @param	string	$str

	 * @param	int	$start

	 * @param	int	$length

	 * @return	string

	 */

	protected static function substr($str, $start, $length = NULL)

	{

		if (self::$func_override)

		{

			// mb_substr($str, $start, null, '8bit') returns an empty

			// string on PHP 5.3

			isset($length) OR $length = ($start >= 0 ? self::strlen($str) - $start : -$start);

			return mb_substr($str, $start, $length, '8bit');

		}

		return isset($length)

			? substr($str, $start, $length)

			: substr($str, $start);

	}

}