<?php
/*
 * Author: Ryan Gilfether
 * URL: http://www.gilfether.com/phpCrypt
 * Date: March 29, 2013
 * Copyright (C) 2013 Ryan Gilfether
 *
 * This file is part of phpCrypt
 *
 * phpCrypt is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 3 of the License, or
 * (at your option) any later version
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, see <http://www.gnu.org/licenses/>.
 */

namespace PHP_Crypt;
require_once(dirname(__FILE__)."/../Cipher.php");
require_once(dirname(__FILE__)."/../Mode.php");
require_once(dirname(__FILE__)."/../phpCrypt.php");


/**
 * Implements Output Feedback (OFB) block cipher mode
 *
 * @author Ryan Gilfether
 * @link http://www.gilfether.com/phpcrypt
 * @copyright 2013 Ryan Gilfether
 */
class Mode_OFB extends Mode
{
	/**
	 * Constructor
	 * Sets the cipher object that will be used for encryption
	 *
	 * @param object $cipher one of the phpCrypt encryption cipher objects
	 * @return void
	 */
	public function __construct($cipher)
	{
		parent::__construct(PHP_Crypt::MODE_OFB, $cipher);

		// this works with only block Ciphers
		if($cipher->type() != Cipher::BLOCK)
			trigger_error("OFB mode requires a block cipher", E_USER_WARNING);
	}


	/**
	 * Destructor
	 *
	 * @return void
	 */
	public function __destruct()
	{
		parent::__destruct();
	}


	/**
	 * Encrypts an the entire string $plain_text using the cipher passed
	 *
	 * @param string $text the string to be encrypted
	 * @return boolean Returns true
	 */
	public function encrypt(&$text)
	{
		$max = strlen($text);
		for($i = 0; $i < $max; ++$i)
		{
			$this->enc_register = $this->register;
			$this->cipher->encrypt($this->enc_register);
			$text[$i] = $text[$i] ^ $this->enc_register[0];

			// shift the register left
			$this->register = substr($this->register, 1);
			$this->register .= $this->enc_register[0];
		}

		return true;
	}


	/**
	 * Decrypts an the entire string $plain_text using the cipher passed
	 *
	 * @param string $text the string to be decrypted
	 * @return boolean Returns true
	 */
	public function decrypt(&$text)
	{
		$max = strlen($text);
		for($i = 0; $i < $max; ++$i)
		{
			$this->enc_register = $this->register;
			$this->cipher->encrypt($this->enc_register);

			// shift the register left
			$this->register = substr($this->register, 1);
			$this->register .= $this->enc_register[0];

			$text[$i] = $text[$i] ^ $this->enc_register[0];
		}

		return true;
	}


	/**
	 * This mode requires an IV
	 *
	 * @return boolean true
	 */
	public function requiresIV()
	{
		return true;
	}
}
?>