Alpha & Protect PDF file

<?php
require('fpdf.php');
//=== AlphaPDF class ==
//-- extends this class from FPDF class
class AlphaPDF extends FPDF
{
    var $extgstates;
    function AlphaPDF($orientation='P', $unit='mm', $format='A4')
    {
        parent::FPDF($orientation, $unit, $format);
        $this->extgstates = array();
    }
    function SetAlpha($alpha, $bm='Normal')
    {
        $gs = $this->AddExtGState(array('ca'=>$alpha, 'CA'=>$alpha, 'BM'=>'/'.$bm));
        $this->SetExtGState($gs);
    }
    function AddExtGState($parms)
    {
        $n = count($this->extgstates)+1;
        $this->extgstates[$n]['parms'] = $parms;
        return $n;
    }
    function SetExtGState($gs)
    {
        $this->_out(sprintf('/GS%d gs', $gs));
    }
    function _enddoc()
    {
        if(!empty($this->extgstates) && $this->PDFVersion<'1.4')
            $this->PDFVersion='1.4';
        parent::_enddoc();
    }
    function _putextgstates()
    {
        for ($i = 1; $i <= count($this->extgstates); $i++)
        {
            $this->_newobj();
            $this->extgstates[$i]['n'] = $this->n;
            $this->_out('<</Type /ExtGState');
            foreach ($this->extgstates[$i]['parms'] as $k=>$v)
                $this->_out('/'.$k.' '.$v);
            $this->_out('>>');
            $this->_out('endobj');
        }
    }
    function _putresourcedict()
    {
        parent::_putresourcedict();
        $this->_out('/ExtGState <<');
        foreach($this->extgstates as $k=>$extgstate)
            $this->_out('/GS'.$k.' '.$extgstate['n'].' 0 R');
        $this->_out('>>');
    }
    function _putresources()
    {
        $this->_putextgstates();
        parent::_putresources();
    }
}
if(function_exists('mcrypt_encrypt'))
{
    function RC4($key, $data)
    {
        return mcrypt_encrypt(MCRYPT_ARCFOUR, $key, $data, MCRYPT_MODE_STREAM, '');
    }
}
else
{
    function RC4($key, $data)
    {
        static $last_key, $last_state;

        if($key != $last_key)
        {
            $k = str_repeat($key, 256/strlen($key)+1);
            $state = range(0, 255);
            $j = 0;
            for ($i=0; $i<256; $i++){
                $t = $state[$i];
                $j = ($j + $t + ord($k[$i])) % 256;
                $state[$i] = $state[$j];
                $state[$j] = $t;
            }
            $last_key = $key;
            $last_state = $state;
        }
        else
            $state = $last_state;

        $len = strlen($data);
        $a = 0;
        $b = 0;
        $out = '';
        for ($i=0; $i<$len; $i++){
            $a = ($a+1) % 256;
            $t = $state[$a];
            $b = ($b+$t) % 256;
            $state[$a] = $state[$b];
            $state[$b] = $t;
            $k = $state[($state[$a]+$state[$b]) % 256];
            $out .= chr(ord($data[$i]) ^ $k);
        }
        return $out;
    }
}
//==== FPDF_Protection  class ===
// do this trick:
// -- extends this class from AlphaPDF class not from FPDF class
class FPDF_Protection extends AlphaPDF
{
    var $encrypted = false;
    var $Uvalue;
    var $Ovalue;
    var $Pvalue;
    var $enc_obj_id;
    function SetProtection($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->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";
        $this->_generateencryptionkey($user_pass, $owner_pass, $protection);
    }
    function _putstream($s)
    {
        if ($this->encrypted) {
            $s = RC4($this->_objectkey($this->n), $s);
        }
        parent::_putstream($s);
    }
    function _textstring($s)
    {
        if ($this->encrypted) {
            $s = RC4($this->_objectkey($this->n), $s);
        }
        return parent::_textstring($s);
    }
    function _objectkey($n)
    {
        return substr($this->_md5_16($this->encryption_key.pack('VXxx',$n)),0,10);
    }
    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');
            $this->_out('/ID [()()]');
        }
    }
    function _md5_16($string)
    {
        return pack('H*',md5($string));
    }
    function _Ovalue($user_pass, $owner_pass)
    {
        $tmp = $this->_md5_16($owner_pass);
        $owner_RC4_key = substr($tmp,0,5);
        return RC4($owner_RC4_key, $user_pass);
    }
    function _Uvalue()
    {
        return RC4($this->encryption_key, $this->padding);
    }
   function _generateencryptionkey($user_pass, $owner_pass, $protection)
    {
        $user_pass = substr($user_pass.$this->padding,0,32);
        $owner_pass = substr($owner_pass.$this->padding,0,32);
        $this->Ovalue = $this->_Ovalue($user_pass,$owner_pass);
        $tmp = $this->_md5_16($user_pass.$this->Ovalue.chr($protection)."\xFF\xFF\xFF");
        $this->encryption_key = substr($tmp,0,5);
        $this->Uvalue = $this->_Uvalue();
        $this->Pvalue = -(($protection^255)+1);
    }
}
//-- create new object from FPDF_Protection class
$pdf = new FPDF_Protection();
$pdf->AddPage();
$pdf->SetLineWidth(1.5);
$pdf->SetFillColor(255,0,0);
$pdf->Rect(10,10,40,40,'DF');
$pdf->SetAlpha(0.5);
$pdf->SetFillColor(0,255,0);
$pdf->Rect(20,20,40,40,'DF');
$pdf->Image('lena.jpg',30,30,40);
$pdf->SetAlpha(1);
$pdf->SetFont('Arial', '', 12);
$pdf->Text(46,68,'Lena');
$pdf->SetProtection(array('print'));
$pdf->AddPage();
$pdf->SetFont('Arial');
$pdf->Write(10,'You can print me but not copy my text.');
$pdf->Output();
?>