summaryrefslogtreecommitdiffstats
path: root/system/libraries/Encryption.php
blob: 2d3f82dc89464f91161e64f4074a80e598607bab (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
<?php
/**
 * CodeIgniter
 *
 * An open source application development framework for PHP 5.2.4 or newer
 *
 * NOTICE OF LICENSE
 *
 * Licensed under the Open Software License version 3.0
 *
 * This source file is subject to the Open Software License (OSL 3.0) that is
 * bundled with this package in the files license.txt / license.rst.  It is
 * also available through the world wide web at this URL:
 * http://opensource.org/licenses/OSL-3.0
 * If you did not receive a copy of the license and are unable to obtain it
 * through the world wide web, please send an email to
 * licensing@ellislab.com so we can send you a copy immediately.
 *
 * @package		CodeIgniter
 * @author		EllisLab Dev Team
 * @copyright	Copyright (c) 2008 - 2013, EllisLab, Inc. (http://ellislab.com/)
 * @license		http://opensource.org/licenses/OSL-3.0 Open Software License (OSL 3.0)
 * @link		http://codeigniter.com
 * @since		Version 3.0
 * @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 = 'rijndael-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 supported HMAC algorightms
	 *
	 * name => digest size pairs
	 *
	 * @var	array
	 */
	protected $_digests = array(
		'sha224' => 28,
		'sha256' => 32,
		'sha384' => 48,
		'sha512' => 64
	);

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

	/**
	 * Class constructor
	 *
	 * @param	array	$params	Configuration parameters
	 * @return	void
	 */
	public function __construct(array $params = array())
	{
		$this->_drivers = array(
			'mcrypt' => extension_loaded('mcrypt'),
			// 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'] && ! $this->_drivers['openssl'])
		{
			return show_error('Encryption: Unable to find an available encryption driver.');
		}
		// Our configuration validates against the existence of MCRYPT_MODE_* constants,
		// but MCrypt supports CTR mode without actually having a constant for it, so ...
		elseif ($this->_drivers['mcrypt'] && ! defined('MCRYPT_MODE_CTR'))
		{
			define('MCRYPT_MODE_CTR', 'ctr');
		}

		$this->initialize($params);

		isset($this->_key) OR $this->_key = config_item('encryption_key');
		if (empty($this->_key))
		{
			return show_error('Encryption: You are required to set an encryption key in your configuration.');
		}

		log_message('debug', '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['mcrypt'] === TRUE)
				? 'mcrypt'
				: 'openssl';

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

		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($params['mode']))
		{
			if ( ! defined('MCRYPT_MODE_'.$params['mode']))
			{
				log_message('error', 'Encryption: MCrypt mode '.strtotupper($params['mode']).' is not available.');
			}
			else
			{
				$this->_mode = constant('MCRYPT_MODE_'.$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, '', $this->_mode, ''))
			{
				log_message('debug', 'Encryption: MCrypt cipher '.strtoupper($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']))
		{
			$this->_mode = strtolower($params['mode']);
		}

		if (isset($this->_cipher, $this->_mode))
		{
			// OpenSSL methods aren't suffixed with '-stream' for this mode
			$handle = ($this->_mode === 'stream')
				? $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 = $handle;
				log_message('debug', 'Encryption: OpenSSL initialized with method '.strtoupper($handle).'.');
			}
		}
	}

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

	/**
	 * 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;
		}
		elseif ( ! isset($params['iv']))
		{
			$params['iv'] = ($iv_size = $this->{'_'.$this->_driver.'_get_iv_size'}($params['handle']))
				? $this->{'_'.$this->_driver.'_get_iv'}($iv_size)
				: NULL;
		}

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

		if ($params['base64'])
		{
			$data = base64_encode($data);
		}

		if ($params['hmac'] !== FALSE)
		{
			if ( ! isset($params['hmac']['key']))
			{
				$params['hmac']['key'] = $this->hkdf(
					$params['key'],
					$params['hmac']['digest'],
					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;
		}
		elseif (mcrypt_generic_init($params['handle'], $params['key'], $params['iv']) < 0)
		{
			if ($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
		$block_size = mcrypt_enc_get_block_size($params['handle']);
		$pad = $block_size - (strlen($data) % $block_size);
		$data .= str_repeat(chr($pad), $pad);

		$data = $params['iv'].mcrypt_generic($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;
		}

		$data = openssl_encrypt(
			$data,
			$params['handle'],
			$params['key'],
			1, // DO NOT TOUCH!
			$params['iv']
		);

		if ($data === FALSE)
		{
			return FALSE;
		}

		return $params['iv'].$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 ($params['hmac'] !== FALSE)
		{
			if ( ! isset($params['hmac']['key']))
			{
				$params['hmac']['key'] = $this->hkdf(
					$params['key'],
					$params['hmac']['digest'],
					NULL,
					NULL,
					'authentication'
				);
			}

			// 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']];
			$hmac = substr($data, 0, $digest_size);
			$data = substr($data, $digest_size);

			if ($hmac !== hash_hmac($params['hmac']['digest'], $data, $params['hmac']['key'], ! $params['base64']))
			{
				return FALSE;
			}
		}

		if ($params['base64'])
		{
			$data = base64_decode($data);
		}

		if ( ! isset($params['iv']))
		{
			$iv_size = $this->{'_'.$this->_driver.'_get_iv_size'}($params['handle']);
			if ($iv_size = $this->{'_'.$this->_driver.'_get_iv_size'}($params['handle']))
			{
				$params['iv'] = substr($data, 0, $iv_size);
				$data = substr($data, $iv_size);
			}
			else
			{
				$params['iv'] = NULL;
			}
		}
		elseif (strncmp($params['iv'], $data, $iv_size = strlen($params['iv'])) === 0)
		{
			$data = substr($data, $iv_size);
		}

		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;
		}
		elseif (mcrypt_generic_init($params['handle'], $params['key'], $params['iv']) < 0)
		{
			if ($params['handle'] !== $this->_handle)
			{
				mcrypt_module_close($params['handle']);
			}

			return FALSE;
		}

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

		mcrypt_generic_deinit($params['handle']);
		if ($params['handle'] !== $this->_handle)
		{
			mcrypt_module_close($params['handle']);
		}

		// Remove PKCS#7 padding
		return substr($data, 0, -ord($data[strlen($data)-1]));
	}

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

	/**
	 * Decrypt via OpenSSL
	 *
	 * @param	string	$data	Encrypted data
	 * @param	array	$params	Input parameters
	 * @return	string
	 */
	protected function _openssl_decrypt($data, $params)
	{
		return empty($params['handle'])
			? FALSE
			: openssl_decrypt(
				$data,
				$params['handle'],
				$params['key'],
				1, // DO NOT TOUCH!
				$params['iv']
			);
	}

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

	/**
	 * Get IV size via MCrypt
	 *
	 * @param	resource	$handle	MCrypt module resource
	 * @return	int
	 */
	protected function _mcrypt_get_iv_size($handle)
	{
		return mcrypt_enc_get_iv_size($handle);
	}

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

	/**
	 * Get IV size via OpenSSL
	 *
	 * @param	string	$handle	OpenSSL cipher method
	 * @return	int
	 */
	protected function _openssl_get_iv_size($handle)
	{
		return openssl_cipher_iv_length($handle);
	}

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

	/**
	 * Get IV via MCrypt
	 *
	 * @param	int	$size
	 * @return	int
	 */
	protected function _mcrypt_get_iv($size)
	{
		// If /dev/urandom is available - use it, otherwise there's
		// also /dev/random, but it is highly unlikely that it would
		// be available while /dev/urandom is not and it is known to be
		// blocking anyway.
		if (defined(MCRYPT_DEV_URANDOM))
		{
			$source = MCRYPT_DEV_URANDOM;
		}
		else
		{
			$source = MCRYPT_RAND;
			is_php('5.3') OR srand(microtime(TRUE));
		}

		return mcrypt_create_iv($size, $source);
	}

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

	/**
	 * Get IV via OpenSSL
	 *
	 * @param	int	$size	IV size
	 * @return	int
	 */
	protected function _openssl_get_iv($size)
	{
		return openssl_random_pseudo_bytes($size);
	}

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

	/**
	 * 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' => $this->_key,
					'base64' => TRUE,
					'hmac' => $this->_mode === 'gcm' ? FALSE : array('digest' => 'sha512',	'key' => NULL)
				)
				: FALSE;
		}
		elseif ( ! isset($params['cipher'], $params['mode'], $params['key']))
		{
			return FALSE;
		}

		if ($params['mode'] === 'gcm')
		{
			$params['hmac'] = FALSE;
		}
		elseif ( ! isset($params['hmac']) OR ( ! is_array($params['hmac']) && $params['hmac'] !== FALSE))
		{
			$params['hmac'] = array(
				'digest' => 'sha512',
				'key' => NULL
			);
		}
		elseif (is_array($params['hmac']))
		{
			if (isset($params['hmac']['digest']) && ! isset($this->_digests[$params['hmac']['digest']]))
			{
				return FALSE;
			}

			$params['hmac'] = array(
				'digest' => isset($params['hmac']['digest']) ? $params['hmac']['digest'] : 'sha512',
				'key' => isset($params['hmac']['key']) ? $params['hmac']['key'] : NULL
			);
		}

		$params = array(
			'handle' => NULL,
			'cipher' => isset($params['cipher']) ? $params['cipher'] : $this->_cipher,
			'mode' => isset($params['mode']) ? $params['mode'] : $this->_mode,
			'key' => isset($params['key']) ? $params['key'] : $this->_key,
			'iv' => isset($params['iv']) ? $params['iv'] : NULL,
			'base64' => isset($params['base64']) ? $params['base64'] : TRUE,
			'hmac' => $params['hmac']
		);

		$this->_cipher_alias($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',
					'rc4-40' => 'arcfour'
				),
				'openssl' => array(
					'rijndael-128' => 'aes-128',
					'tripledes' => 'des-ede3',
					'arcfour' => 'rc4-40'
				)
			);

			// Notes regarding other seemingly matching ciphers between
			// MCrypt and OpenSSL:
			//
			// - DES is compatible, but doesn't need an alias
			// - Blowfish is NOT compatible
			//	mcrypt: 'blowfish', 'blowfish-compat'
			//	openssl: 'bf'
			// - CAST-128/CAST5 is NOT compatible
			//	mcrypt: 'cast-128'
			//	openssl: 'cast5'
			// - RC2 is NOT compatible
			//	mcrypt: 'rc2'
			//	openssl: 'rc2', 'rc2-40', 'rc2-64'
			//
			// To avoid any other confusion due to a popular (but incorrect)
			// belief, it should also be noted that Rijndael-192/256 are NOT
			// the same ciphers as AES-192/256 like Rijndael-128 and AES-256 is.
			//
			// All compatibility tests were done in CBC mode.
		}

		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	$info	Optional context/application-specific info
	 * @param	$length	Output length (defaults to the selected digest size)
	 * @return	string	A pseudo-random key
	 */
	public function hkdf($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;
		}

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

		$prk = hash_hmac($digest, $key, $salt, TRUE);
		$key = '';
		for ($key_block = '', $block_index = 1; strlen($key) < $length; $block_index++)
		{
			$key_block = hash_hmac($digest, $key_block.$info.chr($block_index), $prk, TRUE);
			$key .= $key_block;
		}

		return substr($key, 0, $length);
	}

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

	/**
	 * __get() magic
	 *
	 * @param	string	$key	Property name
	 * @return	mixed
	 */
	public function __get($key)
	{
		return in_array($key, array('cipher', 'mode', 'driver', 'drivers', 'digests'), TRUE)
			? $this->{'_'.$key}
			: NULL;
	}

}

/* End of file Encryption.php */
/* Location: ./system/libraries/Encryption.php */