<?php
/*
ZeroBin - a zero-knowledge paste bin
Please see project page: http://sebsauvage.net/wiki/doku.php?id=php:zerobin
*/
$VERSION='Alpha 0.19';
if (version_compare(PHP_VERSION, '5.2.6') < 0) die('ZeroBin requiert php 5.2.6 ou une version supérieure pour fonctionner. Désolé.');
require_once "lib/serversalt.php";
require_once "lib/vizhash_gd_zero.php";

// In case stupid admin has left magic_quotes enabled in php.ini:
if (get_magic_quotes_gpc())
{
    function stripslashes_deep($value) { $value = is_array($value) ? array_map('stripslashes_deep', $value) : stripslashes($value); return $value; }
    $_POST = array_map('stripslashes_deep', $_POST);
    $_GET = array_map('stripslashes_deep', $_GET);
    $_COOKIE = array_map('stripslashes_deep', $_COOKIE);
}

// trafic_limiter : Make sure the IP address makes at most 1 request every 10 seconds.
// Will return false if IP address made a call less than 10 seconds ago.
function trafic_limiter_canPass($ip)
{
    $tfilename='./data/trafic_limiter.php';
    if (!is_file($tfilename))
    {
        file_put_contents($tfilename,"<?php\n\$GLOBALS['trafic_limiter']=array();\n?>", LOCK_EX);
        chmod($tfilename,0705);
    }
    require $tfilename;
    $tl=$GLOBALS['trafic_limiter'];
    if (!empty($tl[$ip]) && ($tl[$ip]+10>=time()))
    {
        return false;
        // FIXME: purge file of expired IPs to keep it small
    }
    $tl[$ip]=time();
    file_put_contents($tfilename, "<?php\n\$GLOBALS['trafic_limiter']=".var_export($tl,true).";\n?>", LOCK_EX);
    return true;
}

// Constant time string comparison.
// (Used to deter time attacks on hmac checking. See section 2.7 of https://defuse.ca/audits/zerobin.htm)
function slow_equals($a, $b)
{
    $diff = strlen($a) ^ strlen($b);
    for($i = 0; $i < strlen($a) && $i < strlen($b); $i++)
    {
        $diff |= ord($a[$i]) ^ ord($b[$i]);
    }
    return $diff === 0;
}


/* Convert paste id to storage path.
   The idea is to creates subdirectories in order to limit the number of files per directory.
   (A high number of files in a single directory can slow things down.)
   eg. "f468483c313401e8" will be stored in "data/f4/68/f468483c313401e8"
   High-trafic websites may want to deepen the directory structure (like Squid does).

   eg. input 'e3570978f9e4aa90' --> output 'data/e3/57/'
*/
function dataid2path($dataid)
{
    return 'data/'.substr($dataid,0,2).'/'.substr($dataid,2,2).'/';
}

/* Convert paste id to discussion storage path.
   eg. 'e3570978f9e4aa90' --> 'data/e3/57/e3570978f9e4aa90.discussion/'
*/
function dataid2discussionpath($dataid)
{
    return dataid2path($dataid).$dataid.'.discussion/';
}

// Checks if a json string is a proper SJCL encrypted message.
// False if format is incorrect.
function validSJCL($jsonstring)
{
    $accepted_keys=array('iv','v','iter','ks','ts','mode','adata','cipher','salt','ct');

    // Make sure content is valid json
    $decoded = json_decode($jsonstring);
    if ($decoded==null) return false;
    $decoded = (array)$decoded;

    // Make sure required fields are present
    foreach($accepted_keys as $k)
    {
        if (!array_key_exists($k,$decoded))  { return false; }
    }

    // Make sure some fields are base64 data
    if (base64_decode($decoded['iv'],$strict=true)==null) { return false; }
    if (base64_decode($decoded['salt'],$strict=true)==null) { return false; }
    if (base64_decode($decoded['cipher'],$strict=true)==null) { return false; }

    // Make sure no additionnal keys were added.
    if (count(array_intersect(array_keys($decoded),$accepted_keys))!=10) { return false; }

    // Reject data if entropy is too low
    $ct = base64_decode($decoded['ct'], $strict=true);
    if (strlen($ct) > strlen(gzdeflate($ct))) return false;

    // Make sure some fields have a reasonable size.
    if (strlen($decoded['iv'])>24) return false;
    if (strlen($decoded['salt'])>14) return false;
    return true;
}

// Delete a paste and its discussion.
// Input: $pasteid : the paste identifier.
function deletePaste($pasteid)
{
    // Delete the paste itself
    unlink(dataid2path($pasteid).$pasteid);

    // Delete discussion if it exists.
    $discdir = dataid2discussionpath($pasteid);
    if (is_dir($discdir))
    {
        // Delete all files in discussion directory
        $dhandle = opendir($discdir);
        while (false !== ($filename = readdir($dhandle)))
        {
            if (is_file($discdir.$filename))  unlink($discdir.$filename);
        }
        closedir($dhandle);

        // Delete the discussion directory.
        rmdir($discdir);
    }
}

if (!empty($_POST['data'])) // Create new paste/comment
{
    /* POST contains:
         data (mandatory) = json encoded SJCL encrypted text (containing keys: iv,salt,ct)

         All optional data will go to meta information:
         expire (optional) = expiration delay (never,5min,10min,1hour,1day,1week,1month,1year,burn) (default:never)
         opendiscusssion (optional) = is the discussion allowed on this paste ? (0/1) (default:0)
         syntaxcoloring (optional) = should this paste use syntax coloring when displaying.
         nickname (optional) = son encoded SJCL encrypted text nickname of author of comment (containing keys: iv,salt,ct)
         parentid (optional) = in discussion, which comment this comment replies to.
         pasteid (optional) = in discussion, which paste this comment belongs to.
    */

    header('Content-type: application/json');
    $error = false;

    // Create storage directory if it does not exist.
    if (!is_dir('data'))
    {
        mkdir('data',0705);
        file_put_contents('data/.htaccess',"Allow from none\nDeny from all\n", LOCK_EX);
    }

    // Make sure last paste from the IP address was more than 10 seconds ago.
    if (!trafic_limiter_canPass($_SERVER['REMOTE_ADDR']))
        { echo json_encode(array('status'=>1,'message'=>'Veuillez patienter 10 secondes entre chaque message s’il vous plaît.')); exit; }

    // Make sure content is not too big.
    $data = $_POST['data'];
    if (strlen($data)>2000000)
        { echo json_encode(array('status'=>1,'message'=>'Le contenu est limité à 2 Mb de données chiffrées.')); exit; }

    // Make sure format is correct.
    if (!validSJCL($data))
        { echo json_encode(array('status'=>1,'message'=>'Données incorrectes.')); exit; }

    // Read additional meta-information.
    $meta=array();

    // Read expiration date
    if (!empty($_POST['expire']))
    {
        $expire=$_POST['expire'];
        if ($expire=='5min') $meta['expire_date']=time()+5*60;
        elseif ($expire=='10min') $meta['expire_date']=time()+10*60;
        elseif ($expire=='1hour') $meta['expire_date']=time()+60*60;
        elseif ($expire=='1day') $meta['expire_date']=time()+24*60*60;
        elseif ($expire=='1week') $meta['expire_date']=time()+7*24*60*60;
        elseif ($expire=='1month') $meta['expire_date']=time()+30*24*60*60; // Well this is not *exactly* one month, it's 30 days.
        elseif ($expire=='1year') $meta['expire_date']=time()+365*24*60*60;
    }

    // Destroy the paste when it is read.
    if (!empty($_POST['burnafterreading']))
    {
        $burnafterreading = $_POST['burnafterreading'];
        if ($burnafterreading!='0' && $burnafterreading!='1') { $error=true; }
        if ($burnafterreading!='0') { $meta['burnafterreading']=true; }
    }

    // Read open discussion flag
    if (!empty($_POST['opendiscussion']))
    {
        $opendiscussion = $_POST['opendiscussion'];
        if ($opendiscussion!='0' && $opendiscussion!='1') { $error=true; }
        if ($opendiscussion!='0') { $meta['opendiscussion']=true; }
    }

    // Should we use syntax coloring when displaying ?
    if (!empty($_POST['syntaxcoloring']))
    {
        $syntaxcoloring = $_POST['syntaxcoloring'];
        if ($syntaxcoloring!='0' && $syntaxcoloring!='1') { $error=true; }
        if ($syntaxcoloring!='0') { $meta['syntaxcoloring']=true; }
    }    

    // You can't have an open discussion on a "Burn after reading" paste:
    if (isset($meta['burnafterreading'])) unset($meta['opendiscussion']);

    // Optional nickname for comments
    if (!empty($_POST['nickname']))
    {
        $nick = $_POST['nickname'];
        if (!validSJCL($nick))
        {
            $error=true;
        }
        else
        {
            $meta['nickname']=$nick;

            // Generation of the anonymous avatar (Vizhash):
            // If a nickname is provided, we generate a Vizhash.
            // (We assume that if the user did not enter a nickname, he/she wants
            // to be anonymous and we will not generate the vizhash.)
            $vz = new vizhash16x16();
            $pngdata = $vz->generate($_SERVER['REMOTE_ADDR']);
            if ($pngdata!='') $meta['vizhash'] = 'data:image/png;base64,'.base64_encode($pngdata);
            // Once the avatar is generated, we do not keep the IP address, nor its hash.
        }
    }

    if ($error)
    {
        echo json_encode(array('status'=>1,'message'=>'Données incorrectes.'));
        exit;
    }

    // Add post date to meta.
    $meta['postdate']=time();

    // We just want a small hash to avoid collisions: Half-MD5 (64 bits) will do the trick.
    $dataid = substr(hash('md5',$data),0,16);

    $is_comment = (!empty($_POST['parentid']) && !empty($_POST['pasteid'])); // Is this post a comment ?
    $storage = array('data'=>$data);
    if (count($meta)>0) $storage['meta'] = $meta;  // Add meta-information only if necessary.

    if ($is_comment) // The user posts a comment.
    {
        $pasteid = $_POST['pasteid'];
        $parentid = $_POST['parentid'];
        if (!preg_match('/\A[a-f\d]{16}\z/',$pasteid)) { echo json_encode(array('status'=>1,'message'=>'Données incorrectes.')); exit; }
        if (!preg_match('/\A[a-f\d]{16}\z/',$parentid)) { echo json_encode(array('status'=>1,'message'=>'Données incorrectes.')); exit; }

        unset($storage['expire_date']); // Comment do not expire (it's the paste that expires)
        unset($storage['opendiscussion']);
        unset($storage['syntaxcoloring']);

        // Make sure paste exists.
        $storagedir = dataid2path($pasteid);
        if (!is_file($storagedir.$pasteid)) { echo json_encode(array('status'=>1,'message'=>'Données incorrectes.')); exit; }

        // Make sure the discussion is opened in this paste.
        $paste=json_decode(file_get_contents($storagedir.$pasteid));
        if (!$paste->meta->opendiscussion) { echo json_encode(array('status'=>1,'message'=>'Données incorrectes.')); exit; }

        $discdir = dataid2discussionpath($pasteid);
        $filename = $pasteid.'.'.$dataid.'.'.$parentid;
        if (!is_dir($discdir)) mkdir($discdir,$mode=0705,$recursive=true);
        if (is_file($discdir.$filename)) // Oups... improbable collision.
        {
            echo json_encode(array('status'=>1,'message'=>'Vous n’avez pas de chance. Essayez à nouveau.'));
            exit;
        }

        file_put_contents($discdir.$filename,json_encode($storage), LOCK_EX);
        echo json_encode(array('status'=>0,'id'=>$dataid)); // 0 = no error
        exit;
    }
    else // a standard paste.
    {
        $storagedir = dataid2path($dataid);
        if (!is_dir($storagedir)) mkdir($storagedir,$mode=0705,$recursive=true);
        if (is_file($storagedir.$dataid)) // Oups... improbable collision.
        {
            echo json_encode(array('status'=>1,'message'=>'Vous n’avez pas de chance. Essayez à nouveau.'));
            exit;
        }
        // New paste
        file_put_contents($storagedir.$dataid,json_encode($storage), LOCK_EX);

        // Generate the "delete" token.
        // The token is the hmac of the pasteid signed with the server salt.
        // The paste can be delete by calling http://myserver.com/zerobin/?pasteid=<pasteid>&deletetoken=<deletetoken>
        $deletetoken = hash_hmac('sha1', $dataid , getServerSalt());

        echo json_encode(array('status'=>0,'id'=>$dataid,'deletetoken'=>$deletetoken)); // 0 = no error
        exit;
    }

echo json_encode(array('status'=>1,'message'=>'Erreur du serveur.'));
exit;
}

/* Process a paste deletion request.
   Returns an array ('',$ERRORMESSAGE,$STATUS)
*/
function processPasteDelete($pasteid,$deletetoken)
{
    if (preg_match('/\A[a-f\d]{16}\z/',$pasteid))  // Is this a valid paste identifier ?
    {
        $filename = dataid2path($pasteid).$pasteid;
        if (!is_file($filename)) // Check that paste exists.
        {
            return array('','Ce texte n’existe pas, il a expiré ou a été supprimé.','');
        }
    }
    else
    {
        return array('','Données incorrectes.','');
    }

    if (!slow_equals($deletetoken, hash_hmac('sha1', $pasteid , getServerSalt()))) // Make sure token is valid.
    {
        return array('','Mauvais code de suppression. Le texte n’a pu être supprimé.','');
    }

    // Paste exists and deletion token is valid: Delete the paste.
    deletePaste($pasteid);
    return array('','','Texte a bien été supprimé.');
}

/* Process a paste fetch request.
   Returns an array ($CIPHERDATA,$ERRORMESSAGE,$STATUS)
*/
function processPasteFetch($pasteid)
{
    if (preg_match('/\A[a-f\d]{16}\z/',$pasteid))  // Is this a valid paste identifier ?
    {
        $filename = dataid2path($pasteid).$pasteid;
        if (!is_file($filename)) // Check that paste exists.
        {
            return array('','Ce texte n’existe pas, il a expiré ou a été supprimé.','');
        }
    }
    else
    {
        return array('','Données incorrectes.','');
    }

    // Get the paste itself.
    $paste=json_decode(file_get_contents($filename));

    // See if paste has expired.
    if (isset($paste->meta->expire_date) && $paste->meta->expire_date<time())
    {
        deletePaste($pasteid);  // Delete the paste
        return array('','Ce texte n’existe pas, il a expiré ou a été supprimé.','');
    }


    // We kindly provide the remaining time before expiration (in seconds)
    if (property_exists($paste->meta, 'expire_date')) $paste->meta->remaining_time = $paste->meta->expire_date - time();

    $messages = array($paste); // The paste itself is the first in the list of encrypted messages.
    // If it's a discussion, get all comments.
    if (property_exists($paste->meta, 'opendiscussion') && $paste->meta->opendiscussion)
    {
        $comments=array();
        $datadir = dataid2discussionpath($pasteid);
        if (!is_dir($datadir)) mkdir($datadir,$mode=0705,$recursive=true);
        $dhandle = opendir($datadir);
        while (false !== ($filename = readdir($dhandle)))
        {
            if (is_file($datadir.$filename))
            {
                $comment=json_decode(file_get_contents($datadir.$filename));
                // Filename is in the form pasteid.commentid.parentid:
                // - pasteid is the paste this reply belongs to.
                // - commentid is the comment identifier itself.
                // - parentid is the comment this comment replies to (It can be pasteid)
                $items=explode('.',$filename);
                $comment->meta->commentid=$items[1]; // Add some meta information not contained in file.
                $comment->meta->parentid=$items[2];
                $comments[$comment->meta->postdate]=$comment; // Store in table
            }
        }
        closedir($dhandle);
        ksort($comments); // Sort comments by date, oldest first.
        $messages = array_merge($messages, $comments);
    }
    $CIPHERDATA = json_encode($messages);

    // If the paste was meant to be read only once, delete it.
    if (property_exists($paste->meta, 'burnafterreading') && $paste->meta->burnafterreading) deletePaste($pasteid);

    return array($CIPHERDATA,'','');
}



$CIPHERDATA='';
$ERRORMESSAGE='';
$STATUS='';

if (!empty($_GET['deletetoken']) && !empty($_GET['pasteid'])) // Delete an existing paste
{
    list ($CIPHERDATA, $ERRORMESSAGE, $STATUS) = processPasteDelete($_GET['pasteid'],$_GET['deletetoken']);
}
else if (!empty($_SERVER['QUERY_STRING']))  // Return an existing paste.
{
    list ($CIPHERDATA, $ERRORMESSAGE, $STATUS) = processPasteFetch($_SERVER['QUERY_STRING']);    
}

require_once "lib/rain.tpl.class.php";
header('Content-Type: text/html; charset=utf-8');
$page = new RainTPL;
$page->assign('CIPHERDATA',htmlspecialchars($CIPHERDATA,ENT_NOQUOTES));  // We escape it here because ENT_NOQUOTES can't be used in RainTPL templates.
$page->assign('VERSION',$VERSION);
$page->assign('ERRORMESSAGE',$ERRORMESSAGE);
$page->assign('STATUS',$STATUS);
$page->draw('page');
?>