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<?php defined('SYSPATH') or die('No direct script access.');
/**
* The Encrypt library provides two-way encryption of text and binary strings
* using the MCrypt extension.
* @see http://php.net/mcrypt
*
* $Id: Encrypt.php 1911 2008-02-04 16:13:16Z PugFish $
*
* @package Core
* @author Kohana Team
* @copyright (c) 2007-2008 Kohana Team
* @license http://kohanaphp.com/license.html
*/
class Encrypt {

// OS-dependant RAND type to use
protected static $rand;

// Configuration
protected $config;

/**
* Returns a singleton instance of Encrypt.
*
* @param array configuration options
* @return object
*/
public static function instance($config = NULL)
{
static $instance;

// Create the singleton
empty($instance) and $instance = new Encrypt((array) $config);

return $instance;
}

/**
* Loads encryption configuration and validates the data.
*
* @throws Kohana_Exception
*/
public function __construct($config = array())
{
if ( ! defined('MCRYPT_ENCRYPT'))
throw new Kohana_Exception('encrypt.requires_mcrypt');

// Append the default configuration options
$config += Config::item('encryption');

if (empty($config['key']))
throw new Kohana_Exception('encrypt.no_encryption_key');

// Find the max length of the key, based on cipher and mode
$size = mcrypt_get_key_size($config['cipher'], $config['mode']);

if (strlen($config['key']) > $size)
{
// Shorten the key to the maximum size
$config['key'] = substr($config['key'], 0, $size);
}

// Find the initialization vector size
$config['iv_size'] = mcrypt_get_iv_size($config['cipher'], $config['mode']);

// Cache the config in the object
$this->config = $config;

Log::add('debug', 'Encrypt Library initialized');
}

/**
* Encrypts a string and returns an encrypted string that can be decoded.
*
* @param string data to be encrypted
* @return string encrypted data
*/
public function encode($data)
{
// Set the rand type if it has not already been set
if (self::$rand === NULL)
{
if (defined('MCRYPT_DEV_URANDOM'))
{
// Use /dev/urandom
self::$rand = MCRYPT_DEV_URANDOM;
}
elseif (defined('MCRYPT_DEV_RANDOM'))
{
// Use /dev/random
self::$rand = MCRYPT_DEV_RANDOM;
}
else
{
// Use the system random number generator
self::$rand = MCRYPT_RAND;
}
}

if (self::$rand === MCRYPT_RAND)
{
// The system random number generator must always be seeded each
// time it is used, or it will not produce true random results
mt_srand();
}

// Create a random initialization vector of the proper size for the current cipher
$iv = mcrypt_create_iv($this->config['iv_size'], self::$rand);

// Encrypt the data using the configured options and generated iv
$data = mcrypt_encrypt($this->config['cipher'], $this->config['key'], $data, $this->config['mode'], $iv);

// Use base64 encoding to convert to a string
return base64_encode($iv.$data);
}

/**
* Decrypts an encoded string back to it's original value.
*
* @param string encoded string to be decrypted
* @return string decrypted data
*/
public function decode($data)
{
// Convert the data back to binary
$data = base64_decode($data);

// Extract the initialization vector from the data
$iv = substr($data, 0, $this->config['iv_size']);

// Remove the iv from the data
$data = substr($data, $this->config['iv_size']);

// Return the decrypted data, trimming the \0 padding bytes from the end of the data
return rtrim(mcrypt_decrypt($this->config['cipher'], $this->config['key'], $data, $this->config['mode'], $iv), "\0");
}

} // End Encrypt
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