Bonjour,

J'ai utilisé un script existant sur le site [url]http://www.fpdf.org/[/url] pour pouvoir ajouter une encryption dans le fichier pdf afin de limiter les possibilités d'impressions, modifications, ...

Le code est ci-dessous.

Une fois le pdf généré, si dans acrobat reader, on va dans "Détails des droits"->Onglet Protection->Bouton afficher les détails... On peut lire "Niveau de chiffrement: Faible (RC4 à 40 bites)"

Je voudrais changer le niveau de chiffrement et passer à "Niveau de chiffrement: Elevé (RC4 à 128 bits)"

J'ai bien sûr trouver des solutions payantes... j'ai même téléchargé les spécifications du layout des fichiers pdf (pas évident de s'y retrouver et de comprendre ce qu'il faut modifier), ...

Bref qqu'un a-t-il une piste?


[code]
<?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);
}
}

?>
[/code]