<?php
/** @package    php-gpg */

/** require supporting files */
require_once("GPG/Expanded_Key.php");
require_once("GPG/Public_Key.php");
require_once("GPG/AES.php");
require_once("GPG/globals.php");

/**
 * Pure PHP implementation of PHP/GPG encryption.  
 * Supports RSA, DSA public key length of 2,4,8,16,512,1024,2048 or 4096
 * Currently supports only encrypt
 *
 * @package php-gpg::Encryption
 * @link http://www.verysimple.com/
 * @copyright 1997-2012 VerySimple, Inc.
 * @license http://www.gnu.org/licenses/gpl.html  GPL
 * @todo implement decryption
 * @version 1.1
 * 
 * @example 
 * 		require_once 'libs/GPG.php';
 * 		$gpg = new GPG();
 * 		$pub_key = new GPG_Public_Key($public_key_ascii);
 * 		$encrypted = $gpg->encrypt($pub_key,$plain_text_string);
 */
class GPG 
{

	private $width = 16;
	private $el = array(3, 5, 9, 17, 513, 1025, 2049, 4097);
	private $version = "1.4.7";

	private function gpg_encrypt($key, $text) {

		$i = 0;
		$len = strlen($text);
		$iblock = array_fill(0, $this->width, 0);
		$rblock = array_fill(0, $this->width, 0);
		$ct = array_fill(0, $this->width + 2, 0);
	 
		$cipher = "";

		if($len % $this->width) {
			for($i = ($len % $this->width); $i < $this->width; $i++) $text .= "\0";
		}
	 
		$ekey = new Expanded_Key($key);

		for($i = 0; $i < $this->width; $i++) {
			$iblock[$i] = 0;
			$rblock[$i] = GPG_Utility::c_random();
		}


		$iblock = GPG_AES::encrypt($iblock, $ekey);
		for($i = 0; $i < $this->width; $i++) {
			$ct[$i] = ($iblock[$i] ^= $rblock[$i]);
		}

		$iblock = GPG_AES::encrypt($iblock, $ekey);
		$ct[$this->width]   = ($iblock[0] ^ $rblock[$this->width - 2]);
		$ct[$this->width + 1] = ($iblock[1] ^ $rblock[$this->width - 1]);
	 
		for($i = 0; $i < $this->width + 2; $i++) $cipher .= chr($ct[$i]);

		$iblock = array_slice($ct, 2, $this->width + 2);

		for($n = 0; $n < strlen($text); $n += $this->width) {
			$iblock = GPG_AES::encrypt($iblock, $ekey);
			for($i = 0; $i < $this->width; $i++) {
				$iblock[$i] ^= ord($text[$n + $i]);
				$cipher .= chr($iblock[$i]);
			}
		}
	 
		return substr($cipher, 0, $len + $this->width + 2);
	}

	private function gpg_header($tag, $len)
	{
		$h = "";
		if ($len < 0x100) {
		  $h .= chr($tag);
		  $h .= chr($len);
		} else if ($len < 0x10000) {
		  $tag+=1;
		  $h .= chr($tag);
		  $h .= $this->writeNumber($len, 2);
		} else {
		  $tag+=2;
		  $h .= chr($tag);
		  $h .= $this->writeNumber($len, 4);
		}
		return $h;
	}

	private function writeNumber($n, $bytes)
	{
		// credits for this function go to OpenPGP.js
		$b = '';
		for ($i = 0; $i < $bytes; $i++) {
		  $b .= chr(($n >> (8 * ($bytes - $i - 1))) & 0xff);
		}
		return $b;
	}

	private function gpg_session($key_id, $key_type, $session_key, $public_key)
	{ 

		$mod = array();
		$exp = array();
		$enc = "";
	 
		$s = base64_decode($public_key);
		$l = floor((ord($s[0]) * 256 + ord($s[1]) + 7) / 8);
		$mod = mpi2b(substr($s, 0, $l + 2));
		if($key_type) {
			$grp = array();
			$y = array();
			$B = array();
			$C = array();

			$l2 = floor((ord($s[$l + 2]) * 256 + ord($s[$l + 3]) + 7) / 8) + 2;
			$grp = mpi2b(substr($s, $l + 2, $l2));
			$y = mpi2b(substr($s, $l + 2 + $l2));
			$exp[0] = $this->el[GPG_Utility::c_random() & 7];
			$B = bmodexp($grp, $exp, $mod);
			$C = bmodexp($y, $exp, $mod);
		} else {
			$exp = mpi2b(substr($s, $l + 2));
		}

		$c = 0;
		$lsk = strlen($session_key);
		for($i = 0; $i < $lsk; $i++) $c += ord($session_key[$i]);
		$c &= 0xffff;

		$lm = ($l - 2) * 8 + 2;
		$m = chr($lm / 256) . chr($lm % 256) .
			chr(2) . GPG_Utility::s_random($l - $lsk - 6, 1) . "\0" .
			chr(7) . $session_key .
			chr($c / 256) . chr($c & 0xff);

		if($key_type) {
			$enc = b2mpi($B) . b2mpi(bmod(bmul(mpi2b($m), $C), $mod));
			return $this->gpg_header(0x84,strlen($enc) + 10) .
				chr(3) . $key_id . chr(16) . $enc;
		} else {
			$enc = b2mpi(bmodexp(mpi2b($m), $exp, $mod));
			return $this->gpg_header(0x84, strlen($enc) + 10) .
				chr(3) . $key_id . chr(1) . $enc;
		}
	}

	private function gpg_literal($text)
	{
		if (strpos($text, "\r\n") === false)
			$text = str_replace("\n", "\r\n", $text);

		return
		$this->gpg_header(0xac, strlen($text) + 10) . "t" .
			chr(4) . "file\0\0\0\0" . $text;
	}

	private function gpg_data($key, $text)
	{
		$enc = $this->gpg_encrypt($key, $this->gpg_literal($text));
		return $this->gpg_header(0xa4, strlen($enc)) . $enc;
	}

	/**
	 * GPG Encypts a message to the provided public key
	 *
	 * @param GPG_Public_Key $pk
	 * @param string $plaintext
	 * @return string encrypted text
	 */
	function encrypt($pk, $plaintext)
	{
		// normalize the public key
		$key_id = $pk->GetKeyId();
		$key_type = $pk->GetKeyType();
		$public_key = $pk->GetPublicKey();

		$session_key = GPG_Utility::s_random($this->width, 0);
		$key_id = GPG_Utility::hex2bin($key_id);
		$cp = $this->gpg_session($key_id, $key_type, $session_key, $public_key) .
			$this->gpg_data($session_key, $plaintext);

		$code = base64_encode($cp);
		$code = wordwrap($code, 64, "\n", 1);

		return
			"-----BEGIN PGP MESSAGE-----\nVersion: VerySimple PHP-GPG v".$this->version."\n\n" .
			$code . "\n=" . base64_encode(GPG_Utility::crc24($cp)) .
			"\n-----END PGP MESSAGE-----\n";
	}
}

?>