PHP Funda: PDF Protection

Informations

Author: Klemen Vodopivec

License: Freeware

Description

This script allows to protect the PDF, that is to say prevent people from copying its content, print it or modify it.

SetProtection([array permissions [, string user_pass [, string owner_pass]]])

permissions: the set of permissions. Empty by default (only viewing is allowed).

user_pass: user password. Empty by default.

owner_pass: owner password. If not specified, a random value is used.

The permission array is composed of values taken from the following ones:

copy: copy text and images to the clipboard

print: print the document

modify: modify it (except for annotations and forms)

annot-forms: add annotations and forms

Remark: the protection against modification is for people who have the full Acrobat product.

If you don't set any password, the document will open as usual. If you set a user password, the PDF viewer will ask for it before displaying the document. The master password, if different from the user one, can be used to get full access.

Note: protecting a document requires to encrypt it, which increases the processing time a lot. This can cause a PHP time-out in some cases, especially if the document contains images or fonts.

Source

<?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('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);

    }

}

?>

Example

This example shows how to allow only printing.

<?php

define('FPDF_FONTPATH','font/');

require('fpdf_protection.php');

$pdf=new FPDF_Protection();

$pdf->SetProtection(array('print'));

$pdf->Open();

$pdf->AddPage();

$pdf->SetFont('Arial');

$pdf->Write(10,'You can print me but not copy my text.');

$pdf->Output();

?>

View the result here.