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145 lines
3.5 KiB
145 lines
3.5 KiB
<?php
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/*
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* Author: Ryan Gilfether
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* URL: http://www.gilfether.com/phpCrypt
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* Date: Sep 4, 2005
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* Copyright (C) 2005 Ryan Gilfether
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*
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* This file is part of phpCrypt
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*
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* phpCrypt is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 3 of the License, or
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* (at your option) any later version
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, see <http://www.gnu.org/licenses/>.
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*/
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namespace PHP_CRYPT;
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require_once(dirname(__FILE__)."/../Cipher.php");
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require_once(dirname(__FILE__)."/../phpCrypt.php");
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/**
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* An example class that implements a simple Exclusive OR (XOR) encryption
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* cipher using the user supplied key.
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*
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* A SimpleXOR cipher is the same as a One Time Pad when the key length
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* is the same as the data length, and the key is changed after every round
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* of encryption.
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*
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* XOR encryption is very difficult to break, however it can be susceptible
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* to patterns. Thus it is not recommended to use this Cipher for very
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* sensitive data, instead use one of the more secure ciphers (AES, 3DES,
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* Blowfish, etc)
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*
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* @author Ryan Gilfether
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* @link http://www.gilfether.com/phpcrypt
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* @copyright 2005 Ryan Gilfether
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*/
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class Cipher_Simple_XOR extends Cipher
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{
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/** @type integer BYTES_BLOCK The size of the block, in bytes */
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const BYTES_BLOCK = 1; // 8 bits
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/**
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* Constructor
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* Sets the key used for encryption. Also sets the requied block size
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*
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* @param string $key string containing the user supplied encryption key
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* @return void
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*/
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public function __construct($key)
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{
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// SimpleXOR does not have a key size requirement
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parent::__construct(PHP_Crypt::CIPHER_SIMPLEXOR, $key);
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// required block size in bits
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$this->blockSize(self::BYTES_BLOCK);
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}
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/**
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* Destructor
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*
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* @return void
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*/
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public function __destruct()
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{
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parent::__destruct();
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}
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/**
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* Encrypts data using an XOR encryption scheme
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*
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* @param string $text A string to encrypt
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* @return boolean Always returns true
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*/
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public function encrypt(&$text)
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{
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$this->operation(parent::ENCRYPT);
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return $this->simpleXOR($text);
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}
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/**
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* Decrypts data encrypted with SimpleXOR::Encrypt()
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*
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* @param string $text An encrypted string to decrypt
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* @return boolean Always returns true
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*/
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public function decrypt(&$text)
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{
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$this->operation(parent::DECRYPT);
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return $this->simpleXOR($text);
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}
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/**
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* Because XOR Encryption uses the same algorithm to encrypt and decrypt,
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* this function contains the code to do both. The SimpleXOR::Encrypt()
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* and SimpleXOR::Decrypt() function above just call this function
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*
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* @param string $input
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* @return boolean Always returns true
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*/
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private function simpleXOR(&$text)
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{
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$pos = 0;
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$max = strlen($text);
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$key = $this->key();
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for($i = 0; $i < $max; ++$i)
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{
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// if the current position in the key reaches the end of the key,
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// start over at position 0 of the key
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if($pos >= $this->keySize())
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$pos = 0;
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$text[$i] = $text[$i] ^ $key[$pos];
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++$pos;
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}
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return true;
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}
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/**
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* Indicates that this is stream cipher
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*
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* @return integer Returns Cipher::STREAM
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*/
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public function type()
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{
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return parent::STREAM;
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}
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}
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?>
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