Last days, I’ve implemented authentication in Wisss. The goal is to have a secure authentication without the need to use SSL. I’ve then choose a basic Challenge Response Authentication Mechanism which prevent to send password in clear text.
The mechanisme is simple :
- The server send a unique salt, which can be used only once
- The client answer with its username and SHA1(salt+SHA1(password))
- The server retrieves user’s password SHA1 from database and do SHA1(salt,sha1_password)
- if the two match, the user is authenticated
Here is the code for the server (it’s inside a Zend controller, but it can easily be implemented for all framework/language) :
The CRAM authentication adapter for Zend_Auth :
class Wisss_Auth_Adapter_BasicCram implements Zend_Auth_Adapter_Interface
protected $login ;
protected $digest ;
public funtion __construct($login,$digest)
{
$this->login = $login ;
$this->digest = $digest ;
}
public function authenticate()
{
$auth_session = new Zend_Session_Namespace('auth');
// retrieve salt from session and erase it since it's used once
$salt = $auth_session->salt ;
unset($auth_session->salt) ;
// digest received from client
$cram_from_client = $this->digest ;
// retrieve password sha1 digest from database for the user provided
require_once('Wisss/Dao/Factory/Abstract.php') ;
$dao_user = Wisss_Dao_Factory_Abstract::getDao('User','core') ;
$user = $dao_user->findBy(array('login' => $this->login)) ;
$sha1_password = $user[0]->getPassword() ;
// compute the CRAM digest
$cram_from_server = sha1($salt.$sha1_password) ;
if($cram_from_client == $cram_from_server) {
return new Zend_Auth_Result(Zend_Auth_Result::SUCCESS,$this->login) ;
} else {
return new Zend_Auth_Result(Zend_Auth_Result::FAILURE,$this->login) ;
}
}
}
The code of the controller :
class LoginController extends Zend_Controller_Action
{
public function indexAction()
{
$salt = md5(uniqid(rand(), true)) ;
$auth_session = new Zend_Session_Namespace('auth');
$this->view->assign('login_salt',$salt) ;
$auth_session->salt = $salt ;
$auth_session->referer = $_SERVER['HTTP_REFERER'] ;
}
public function authenticateAction()
{
$auth_session = new Zend_Session_Namespace('auth');
require_once 'Zend/Auth.php';
$auth = Zend_Auth::getInstance();
// Set up the authentication adapter
require_once('Wisss/Auth/Adapter/BasicCram.php') ;
$authAdapter = new Wisss_Auth_Adapter_BasicCram($this->_getParam('login'), $this->_getParam('password'));
// Attempt authentication, saving the result
$result = $auth->authenticate($authAdapter);
if (!$result->isValid()) {
// Authentication failed
$this->_redirect('/login') ;
} else {
// Authentification succeeded
// regenerate id to prevent session fixation after successfull authentication
Zend_Session::regenerateId();
$referer = $auth_session->referer ;
unset($auth_session->referer) ;
if($referer != $_SERVER['HTTP_REFERER']) {
$this->_redirect($referer) ;
}
}
}
}
and finally, the client code (it requires the Prototype Javascript framework) :
<div>
<form action="login/authenticate" method="POST" onSubmit="cram()">
<?php echo $this->formHidden('login_salt',$this->login_salt) ?>
<fieldset>
<div><label for="login">Login : </label><?php echo $this->formText('login') ?></div>
<div><label for="password">Password : </label><?php echo $this->formPassword('password') ?></div>
<div><input type="submit" name="authenticate" value="login"/></div>
</fieldset>
</form>
</div>
And the associated js :
function cram()
{
$('password').value = sha1Hash($('login_salt').value+sha1Hash($('password').value)) ;
$('login_salt').value = "" ;
}
// © 2002-2005 Chris Veness
// http://www.movable-type.co.uk/scripts/sha1.html
function sha1Hash(msg)
{
// constants [§4.2.1]
var K = [0x5a827999, 0x6ed9eba1, 0x8f1bbcdc, 0xca62c1d6];
// PREPROCESSING
msg += String.fromCharCode(0x80); // add trailing '1' bit to string [§5.1.1]
// convert string msg into 512-bit/16-integer blocks arrays of ints [§5.2.1]
var l = Math.ceil(msg.length/4) + 2; // long enough to contain msg plus 2-word length
var N = Math.ceil(l/16); // in N 16-int blocks
var M = new Array(N);
for (var i=0; i<N; i++) {
M[i] = new Array(16);
for (var j=0; j<16; j++) { // encode 4 chars per integer, big-endian encoding
M[i][j] = (msg.charCodeAt(i*64+j*4)<<24) | (msg.charCodeAt(i*64+j*4+1)<<16) |
(msg.charCodeAt(i*64+j*4+2)<<8) | (msg.charCodeAt(i*64+j*4+3));
}
}
// add length (in bits) into final pair of 32-bit integers (big-endian) [5.1.1]
// note: most significant word would be ((len-1)*8 >>> 32, but since JS converts
// bitwise-op args to 32 bits, we need to simulate this by arithmetic operators
M[N-1][14] = ((msg.length-1)*8) / Math.pow(2, 32); M[N-1][14] = Math.floor(M[N-1][14])
M[N-1][15] = ((msg.length-1)*8) & 0xffffffff;
// set initial hash value [§5.3.1]
var H0 = 0x67452301;
var H1 = 0xefcdab89;
var H2 = 0x98badcfe;
var H3 = 0x10325476;
var H4 = 0xc3d2e1f0;
// HASH COMPUTATION [§6.1.2]
var W = new Array(80); var a, b, c, d, e;
for (var i=0; i<N; i++) {
// 1 - prepare message schedule 'W'
for (var t=0; t<16; t++) W[t] = M[i][t];
for (var t=16; t<80; t++) W[t] = ROTL(W[t-3] ^ W[t-8] ^ W[t-14] ^ W[t-16], 1);
// 2 - initialise five working variables a, b, c, d, e with previous hash value
a = H0; b = H1; c = H2; d = H3; e = H4;
// 3 - main loop
for (var t=0; t<80; t++) {
var s = Math.floor(t/20); // seq for blocks of 'f' functions and 'K' constants
var T = (ROTL(a,5) + f(s,b,c,d) + e + K[s] + W[t]) & 0xffffffff;
e = d;
d = c;
c = ROTL(b, 30);
b = a;
a = T;
}
// 4 - compute the new intermediate hash value
H0 = (H0+a) & 0xffffffff; // note 'addition modulo 2^32'
H1 = (H1+b) & 0xffffffff;
H2 = (H2+c) & 0xffffffff;
H3 = (H3+d) & 0xffffffff;
H4 = (H4+e) & 0xffffffff;
}
return H0.toHexStr() + H1.toHexStr() + H2.toHexStr() + H3.toHexStr() + H4.toHexStr();
}
//
// function 'f' [§4.1.1]
//
function f(s, x, y, z)
{
switch (s) {
case 0: return (x & y) ^ (~x & z); // Ch()
case 1: return x ^ y ^ z; // Parity()
case 2: return (x & y) ^ (x & z) ^ (y & z); // Maj()
case 3: return x ^ y ^ z; // Parity()
}
}
//
// rotate left (circular left shift) value x by n positions [§3.2.5]
//
function ROTL(x, n)
{
return (x<<n) | (x>>>(32-n));
}
//
// extend Number class with a tailored hex-string method
// (note toString(16) is implementation-dependant, and
// in IE returns signed numbers when used on full words)
//
Number.prototype.toHexStr = function()
{
var s="", v;
for (var i=7; i>=0; i--) { v = (this>>>(i*4)) & 0xf; s += v.toString(16); }
return s;
}
