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<?php
/****************************************************************************
* Software: FPDF_Protection *
* Version: 1.02 *
* Date: 2005/05/08 *
* Author: Klemen VODOPIVEC *
* License: Freeware *
* *
* You may use and modify this software as you wish as stated in original *
* FPDF package. *
* *
* Thanks: Cpdf (http://www.ros.co.nz/pdf) was my working sample of how to *
* implement protection in pdf. *
****************************************************************************/
require_once('fpdf.php');
class FPDF_Protection extends FPDF
{
var $encrypted; //whether document is protected
var $Uvalue; //U entry in pdf document
var $Ovalue; //O entry in pdf document
var $Pvalue; //P entry in pdf document
var $enc_obj_id; //encryption object id
var $last_rc4_key; //last RC4 key encrypted (cached for optimisation)
var $last_rc4_key_c; //last RC4 computed key
function FPDF_Protection($orientation='P',$unit='mm',$format='A4') {
parent::FPDF($orientation,$unit,$format);
$this->encrypted=false;
$this->last_rc4_key='';
$this->padding="\x28\xBF\x4E\x5E\x4E\x75\x8A\x41\x64\x00\x4E\x56\xFF\xFA\x01\x08".
"\x2E\x2E\x00\xB6\xD0\x68\x3E\x80\x2F\x0C\xA9\xFE\x64\x53\x69\x7A";
}
/**
* Function to set permissions as well as user and owner passwords
*
* - permissions is an array with values taken from the following list:
* copy, print, modify, annot-forms
* If a value is present it means that the permission is granted
* - If a user password is set, user will be prompted before document is opened
* - If an owner password is set, document can be opened in privilege mode with no
* restriction if that password is entered
*/
function SetProtection($permissions=array(),$user_pass='',$owner_pass=null) {
$options = array('print' => 4, 'modify' => 8, 'copy' => 16, 'annot-forms' => 32 );
$protection = 192;
foreach($permissions as $permission){
if (!isset($options[$permission]))
$this->Error('Incorrect permission: '.$permission);
$protection += $options[$permission];
}
if ($owner_pass === null)
$owner_pass = uniqid(rand());
$this->encrypted = true;
$this->_generateencryptionkey($user_pass, $owner_pass, $protection);
}
/****************************************************************************
* *
* Private methods *
* *
****************************************************************************/
function _putstream($s) {
if ($this->encrypted) {
$s = $this->_RC4($this->_objectkey($this->n), $s);
}
parent::_putstream($s);
}
function _textstring($s) {
if ($this->encrypted) {
$s = $this->_RC4($this->_objectkey($this->n), $s);
}
return parent::_textstring($s);
}
/**
* Compute key depending on object number where the encrypted data is stored
*/
function _objectkey($n) {
return substr($this->_md5_16($this->encryption_key.pack('VXxx',$n)),0,10);
}
/**
* Escape special characters
*/
function _escape($s) {
$s=str_replace('\\','\\\\',$s);
$s=str_replace(')','\\)',$s);
$s=str_replace('(','\\(',$s);
$s=str_replace("\r",'\\r',$s);
return $s;
}
function _putresources() {
parent::_putresources();
if ($this->encrypted) {
$this->_newobj();
$this->enc_obj_id = $this->n;
$this->_out('<<');
$this->_putencryption();
$this->_out('>>');
$this->_out('endobj');
}
}
function _putencryption() {
$this->_out('/Filter /Standard');
$this->_out('/V 1');
$this->_out('/R 2');
$this->_out('/O ('.$this->_escape($this->Ovalue).')');
$this->_out('/U ('.$this->_escape($this->Uvalue).')');
$this->_out('/P '.$this->Pvalue);
}
function _puttrailer() {
parent::_puttrailer();
if ($this->encrypted) {
$this->_out('/Encrypt '.$this->enc_obj_id.' 0 R');
$this->_out('/ID [()()]');
}
}
/**
* RC4 is the standard encryption algorithm used in PDF format
*/
function _RC4($key, $text) {
if ($this->last_rc4_key != $key) {
$k = str_repeat($key, 256/strlen($key)+1);
$rc4 = range(0,255);
$j = 0;
for ($i=0; $i<256; $i++){
$t = $rc4[$i];
$j = ($j + $t + ord($k{$i})) % 256;
$rc4[$i] = $rc4[$j];
$rc4[$j] = $t;
}
$this->last_rc4_key = $key;
$this->last_rc4_key_c = $rc4;
} else {
$rc4 = $this->last_rc4_key_c;
}
$len = strlen($text);
$a = 0;
$b = 0;
$out = '';
for ($i=0; $i<$len; $i++){
$a = ($a+1)%256;
$t= $rc4[$a];
$b = ($b+$t)%256;
$rc4[$a] = $rc4[$b];
$rc4[$b] = $t;
$k = $rc4[($rc4[$a]+$rc4[$b])%256];
$out.=chr(ord($text{$i}) ^ $k);
}
return $out;
}
/**
* Get MD5 as binary string
*/
function _md5_16($string) {
return pack('H*',md5($string));
}
/**
* Compute O value
*/
function _Ovalue($user_pass, $owner_pass) {
$tmp = $this->_md5_16($owner_pass);
$owner_RC4_key = substr($tmp,0,5);
return $this->_RC4($owner_RC4_key, $user_pass);
}
/**
* Compute U value
*/
function _Uvalue() {
return $this->_RC4($this->encryption_key, $this->padding);
}
/**
* Compute encryption key
*/
function _generateencryptionkey($user_pass, $owner_pass, $protection) {
// Pad passwords
$user_pass = substr($user_pass.$this->padding,0,32);
$owner_pass = substr($owner_pass.$this->padding,0,32);
// Compute O value
$this->Ovalue = $this->_Ovalue($user_pass,$owner_pass);
// Compute encyption key
$tmp = $this->_md5_16($user_pass.$this->Ovalue.chr($protection)."\xFF\xFF\xFF");
$this->encryption_key = substr($tmp,0,5);
// Compute U value
$this->Uvalue = $this->_Uvalue();
// Compute P value
$this->Pvalue = -(($protection^255)+1);
}
}
?>
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