google_forms/system/libraries/Encrypt.php

<?php

/**
 * CodeIgniter
 *
 * An open source application development framework for PHP
 *
 * This content is released under the MIT License (MIT)
 *
 * Copyright (c) 2019 - 2022, CodeIgniter Foundation
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 * The above copyright notice and this permission notice shall be included in
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 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
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 *
 * @package CodeIgniter
 * @author  EllisLab Dev Team
 * @copyright   Copyright (c) 2008 - 2014, EllisLab, Inc. (https://ellislab.com/)
 * @copyright   Copyright (c) 2014 - 2019, British Columbia Institute of Technology (https://bcit.ca/)
 * @copyright   Copyright (c) 2019 - 2022, CodeIgniter Foundation (https://codeigniter.com/)
 * @license https://opensource.org/licenses/MIT MIT License
 * @link    https://codeigniter.com
 * @since   Version 1.0.0
 * @filesource
 */

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

/**
 * CodeIgniter Encryption Class
 *
 * Provides two-way keyed encoding using Mcrypt
 *
 * @package     CodeIgniter
 * @subpackage  Libraries
 * @category    Libraries
 * @author      EllisLab Dev Team
 * @link        https://codeigniter.com/userguide3/libraries/encryption.html
 */
class CI_Encrypt
{
    /**
     * Reference to the user's encryption key
     *
     * @var string
     */
    public $encryption_key      = '';

    /**
     * Type of hash operation
     *
     * @var string
     */
    protected $_hash_type       = 'sha1';

    /**
     * Flag for the existence of mcrypt
     *
     * @var bool
     */
    protected $_mcrypt_exists   = false;

    /**
     * Current cipher to be used with mcrypt
     *
     * @var string
     */
    protected $_mcrypt_cipher;

    /**
     * Method for encrypting/decrypting data
     *
     * @var int
     */
    protected $_mcrypt_mode;

    /**
     * Initialize Encryption class
     *
     * @return  void
     */
    public function __construct()
    {
        if (($this->_mcrypt_exists = function_exists('mcrypt_encrypt')) === false) {
            show_error('The Encrypt library requires the Mcrypt extension.');
        }

        log_message('info', 'Encrypt Class Initialized');
    }

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

    /**
     * Fetch the encryption key
     *
     * Returns it as MD5 in order to have an exact-length 128 bit key.
     * Mcrypt is sensitive to keys that are not the correct length
     *
     * @param   string
     * @return  string
     */
    public function get_key($key = '')
    {
        if ($key === '') {
            if ($this->encryption_key !== '') {
                return $this->encryption_key;
            }

            $key = config_item('encryption_key');

            if (! self::strlen($key)) {
                show_error('In order to use the encryption class requires that you set an encryption key in your config file.');
            }
        }

        return md5($key);
    }

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

    /**
     * Set the encryption key
     *
     * @param   string
     * @return  CI_Encrypt
     */
    public function set_key($key = '')
    {
        $this->encryption_key = $key;
        return $this;
    }

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

    /**
     * Encode
     *
     * Encodes the message string using bitwise XOR encoding.
     * The key is combined with a random hash, and then it
     * too gets converted using XOR. The whole thing is then run
     * through mcrypt using the randomized key. The end result
     * is a double-encrypted message string that is randomized
     * with each call to this function, even if the supplied
     * message and key are the same.
     *
     * @param   string  the string to encode
     * @param   string  the key
     * @return  string
     */
    public function encode($string, $key = '')
    {
        return base64_encode($this->mcrypt_encode($string, $this->get_key($key)));
    }

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

    /**
     * Decode
     *
     * Reverses the above process
     *
     * @param   string
     * @param   string
     * @return  string
     */
    public function decode($string, $key = '')
    {
        if (preg_match('/[^a-zA-Z0-9\/\+=]/', $string) or base64_encode(base64_decode($string)) !== $string) {
            return false;
        }

        return $this->mcrypt_decode(base64_decode($string), $this->get_key($key));
    }

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

    /**
     * Encode from Legacy
     *
     * Takes an encoded string from the original Encryption class algorithms and
     * returns a newly encoded string using the improved method added in 2.0.0
     * This allows for backwards compatibility and a method to transition to the
     * new encryption algorithms.
     *
     * For more details, see https://codeigniter.com/userguide3/installation/upgrade_200.html#encryption
     *
     * @param   string
     * @param   int     (mcrypt mode constant)
     * @param   string
     * @return  string
     */
    public function encode_from_legacy($string, $legacy_mode = MCRYPT_MODE_ECB, $key = '')
    {
        if (preg_match('/[^a-zA-Z0-9\/\+=]/', $string)) {
            return false;
        }

        // decode it first
        // set mode temporarily to what it was when string was encoded with the legacy
        // algorithm - typically MCRYPT_MODE_ECB
        $current_mode = $this->_get_mode();
        $this->set_mode($legacy_mode);

        $key = $this->get_key($key);
        $dec = base64_decode($string);
        if (($dec = $this->mcrypt_decode($dec, $key)) === false) {
            $this->set_mode($current_mode);
            return false;
        }

        $dec = $this->_xor_decode($dec, $key);

        // set the mcrypt mode back to what it should be, typically MCRYPT_MODE_CBC
        $this->set_mode($current_mode);

        // and re-encode
        return base64_encode($this->mcrypt_encode($dec, $key));
    }

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

    /**
     * XOR Decode
     *
     * Takes an encoded string and key as input and generates the
     * plain-text original message
     *
     * @param   string
     * @param   string
     * @return  string
     */
    protected function _xor_decode($string, $key)
    {
        $string = $this->_xor_merge($string, $key);

        $dec = '';
        for ($i = 0, $l = self::strlen($string); $i < $l; $i++) {
            $dec .= ($string[$i++] ^ $string[$i]);
        }

        return $dec;
    }

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

    /**
     * XOR key + string Combiner
     *
     * Takes a string and key as input and computes the difference using XOR
     *
     * @param   string
     * @param   string
     * @return  string
     */
    protected function _xor_merge($string, $key)
    {
        $hash = $this->hash($key);
        $str = '';

        for ($i = 0, $ls = self::strlen($string), $lh = self::strlen($hash); $i < $ls; $i++) {
            $str .= $string[$i] ^ $hash[($i % $lh)];
        }

        return $str;
    }

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

    /**
     * Encrypt using Mcrypt
     *
     * @param   string
     * @param   string
     * @return  string
     */
    public function mcrypt_encode($data, $key)
    {
        $init_size = mcrypt_get_iv_size($this->_get_cipher(), $this->_get_mode());
        $init_vect = mcrypt_create_iv($init_size, MCRYPT_DEV_URANDOM);
        return $this->_add_cipher_noise($init_vect . mcrypt_encrypt($this->_get_cipher(), $key, $data, $this->_get_mode(), $init_vect), $key);
    }

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

    /**
     * Decrypt using Mcrypt
     *
     * @param   string
     * @param   string
     * @return  string
     */
    public function mcrypt_decode($data, $key)
    {
        $data = $this->_remove_cipher_noise($data, $key);
        $init_size = mcrypt_get_iv_size($this->_get_cipher(), $this->_get_mode());

        if ($init_size > self::strlen($data)) {
            return false;
        }

        $init_vect = self::substr($data, 0, $init_size);
        $data      = self::substr($data, $init_size);

        return rtrim(mcrypt_decrypt($this->_get_cipher(), $key, $data, $this->_get_mode(), $init_vect), "\0");
    }

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

    /**
     * Adds permuted noise to the IV + encrypted data to protect
     * against Man-in-the-middle attacks on CBC mode ciphers
     * http://www.ciphersbyritter.com/GLOSSARY.HTM#IV
     *
     * @param   string
     * @param   string
     * @return  string
     */
    protected function _add_cipher_noise($data, $key)
    {
        $key = $this->hash($key);
        $str = '';

        for ($i = 0, $j = 0, $ld = self::strlen($data), $lk = self::strlen($key); $i < $ld; ++$i, ++$j) {
            if ($j >= $lk) {
                $j = 0;
            }

            $str .= chr((ord($data[$i]) + ord($key[$j])) % 256);
        }

        return $str;
    }

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

    /**
     * Removes permuted noise from the IV + encrypted data, reversing
     * _add_cipher_noise()
     *
     * Function description
     *
     * @param   string  $data
     * @param   string  $key
     * @return  string
     */
    protected function _remove_cipher_noise($data, $key)
    {
        $key = $this->hash($key);
        $str = '';

        for ($i = 0, $j = 0, $ld = self::strlen($data), $lk = self::strlen($key); $i < $ld; ++$i, ++$j) {
            if ($j >= $lk) {
                $j = 0;
            }

            $temp = ord($data[$i]) - ord($key[$j]);

            if ($temp < 0) {
                $temp += 256;
            }

            $str .= chr($temp);
        }

        return $str;
    }

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

    /**
     * Set the Mcrypt Cipher
     *
     * @param   int
     * @return  CI_Encrypt
     */
    public function set_cipher($cipher)
    {
        $this->_mcrypt_cipher = $cipher;
        return $this;
    }

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

    /**
     * Set the Mcrypt Mode
     *
     * @param   int
     * @return  CI_Encrypt
     */
    public function set_mode($mode)
    {
        $this->_mcrypt_mode = $mode;
        return $this;
    }

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

    /**
     * Get Mcrypt cipher Value
     *
     * @return  int
     */
    protected function _get_cipher()
    {
        if ($this->_mcrypt_cipher === null) {
            return $this->_mcrypt_cipher = MCRYPT_RIJNDAEL_256;
        }

        return $this->_mcrypt_cipher;
    }

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

    /**
     * Get Mcrypt Mode Value
     *
     * @return  int
     */
    protected function _get_mode()
    {
        if ($this->_mcrypt_mode === null) {
            return $this->_mcrypt_mode = MCRYPT_MODE_CBC;
        }

        return $this->_mcrypt_mode;
    }

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

    /**
     * Set the Hash type
     *
     * @param   string
     * @return  void
     */
    public function set_hash($type = 'sha1')
    {
        $this->_hash_type = in_array($type, hash_algos()) ? $type : 'sha1';
    }

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

    /**
     * Hash encode a string
     *
     * @param   string
     * @return  string
     */
    public function hash($str)
    {
        return hash($this->_hash_type, $str);
    }

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

    /**
     * Byte-safe strlen()
     *
     * @param   string  $str
     * @return  int
     */
    protected static function strlen($str)
    {
        return defined('MB_OVERLOAD_STRING')
            ? 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, $length = null)
    {
        if (defined('MB_OVERLOAD_STRING')) {
            // mb_substr($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);
    }
}