ci-bonfire / Sprint

system/libraries/Encryption.php

<?php

For compatibility and reusability of your code, PSR1 recommends that a file should introduce either new symbols (like classes, functions, etc.) or have side-effects (like outputting something, or including other files), but not both at the same time. The first symbol is defined on line 51 and the first side effect is on line 38.

/**
 * CodeIgniter
 *
 * An open source application development framework for PHP
 *
 * This content is released under the MIT License (MIT)
 *
 * Copyright (c) 2014 - 2015, 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. (http://ellislab.com/)
 * @copyright	Copyright (c) 2014 - 2015, British Columbia Institute of Technology (http://bcit.ca/)
 * @license	http://opensource.org/licenses/MIT	MIT License
 * @link	http://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		http://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'))
		{
			return random_bytes((int) $length);
		}

		return ($this->_driver === 'mcrypt')
			? mcrypt_create_iv($length, MCRYPT_DEV_URANDOM)
			: openssl_random_pseudo_bytes($length);
	}

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

	/**
	 * 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)

It seems like $params defined by $this->_get_params($params) on line 361 can also be of type null; however, CI_Encryption::_get_params() does only seem to accept array, maybe add an additional type check?

		{
			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($params['handle'])) > 1)
			? mcrypt_create_iv($iv_size, MCRYPT_DEV_URANDOM)
			: 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($params['handle']))
			? openssl_random_pseudo_bytes($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)

It seems like $params defined by $this->_get_params($params) on line 496 can also be of type null; however, CI_Encryption::_get_params() does only seem to accept array, maybe add an additional type check?

		{
			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

50% of this comment could be valid code. Did you maybe forget this after debugging?

			// 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);
	}
}