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<?php
// +-----------------------------------------------------------------------+
// | Copyright (c) 2011 Jehan |
// | All rights reserved. |
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// +-----------------------------------------------------------------------+
// | Author: Jehan <jehan.marmottard@gmail.com |
// +-----------------------------------------------------------------------+
//
// $Id$
/**
* Implementation of SCRAM-* SASL mechanisms.
* SCRAM mechanisms have 3 main steps (initial response, response to the server challenge, then server signature
* verification) which keep state-awareness. Therefore a single class instanciation must be done and reused for the whole
* authentication process.
*
* @author Jehan <jehan.marmottard@gmail.com>
* @access public
* @version 1.0
* @package Auth_SASL
*/
require_once('Auth/SASL/Common.php');
class Auth_SASL_SCRAM extends Auth_SASL_Common
{
/**
* Construct a SCRAM-H client where 'H' is a cryptographic hash function.
*
* @param string $hash The name cryptographic hash function 'H' as registered by IANA in the "Hash Function Textual
* Names" registry.
* @link http://www.iana.org/assignments/hash-function-text-names/hash-function-text-names.xml "Hash Function Textual
* Names"
* format of core PHP hash function.
* @access public
*/
function __construct($hash)
{
// Though I could be strict, I will actually also accept the naming used in the PHP core hash framework.
// For instance "sha1" is accepted, while the registered hash name should be "SHA-1".
$hash = strtolower($hash);
$hashes = array('md2' => 'md2',
'md5' => 'md5',
'sha-1' => 'sha1',
'sha1' => 'sha1',
'sha-224' > 'sha224',
'sha224' > 'sha224',
'sha-256' => 'sha256',
'sha256' => 'sha256',
'sha-384' => 'sha384',
'sha384' => 'sha384',
'sha-512' => 'sha512',
'sha512' => 'sha512');
if (function_exists('hash_hmac') && isset($hashes[$hash]))
{
$this->hash = create_function('$data', 'return hash("' . $hashes[$hash] . '", $data, TRUE);');
$this->hmac = create_function('$key,$str,$raw', 'return hash_hmac("' . $hashes[$hash] . '", $str, $key, $raw);');
}
elseif ($hash == 'md5')
{
$this->hash = create_function('$data', 'return md5($data, true);');
$this->hmac = array($this, '_HMAC_MD5');
}
elseif (in_array($hash, array('sha1', 'sha-1')))
{
$this->hash = create_function('$data', 'return sha1($data, true);');
$this->hmac = array($this, '_HMAC_SHA1');
}
else
return PEAR::raiseError('Invalid SASL mechanism type');
}
/**
* Provides the (main) client response for SCRAM-H.
*
* @param string $authcid Authentication id (username)
* @param string $pass Password
* @param string $challenge The challenge sent by the server.
* If the challenge is NULL or an empty string, the result will be the "initial response".
* @param string $authzid Authorization id (username to proxy as)
* @return string|false The response (binary, NOT base64 encoded)
* @access public
*/
public function getResponse($authcid, $pass, $challenge = NULL, $authzid = NULL)
{
$authcid = $this->_formatName($authcid);
if (empty($authcid))
{
return false;
}
if (!empty($authzid))
{
$authzid = $this->_formatName($authzid);
if (empty($authzid))
{
return false;
}
}
if (empty($challenge))
{
return $this->_generateInitialResponse($authcid, $authzid);
}
else
{
return $this->_generateResponse($challenge, $pass);
}
}
/**
* Prepare a name for inclusion in a SCRAM response.
*
* @param string $username a name to be prepared.
* @return string the reformated name.
* @access private
*/
private function _formatName($username)
{
// TODO: prepare through the SASLprep profile of the stringprep algorithm.
// See RFC-4013.
$username = str_replace('=', '=3D', $username);
$username = str_replace(',', '=2C', $username);
return $username;
}
/**
* Generate the initial response which can be either sent directly in the first message or as a response to an empty
* server challenge.
*
* @param string $authcid Prepared authentication identity.
* @param string $authzid Prepared authorization identity.
* @return string The SCRAM response to send.
* @access private
*/
private function _generateInitialResponse($authcid, $authzid)
{
$init_rep = '';
$gs2_cbind_flag = 'n,'; // TODO: support channel binding.
$this->gs2_header = $gs2_cbind_flag . (!empty($authzid)? 'a=' . $authzid : '') . ',';
// I must generate a client nonce and "save" it for later comparison on second response.
$this->cnonce = $this->_getCnonce();
// XXX: in the future, when mandatory and/or optional extensions are defined in any updated RFC,
// this message can be updated.
$this->first_message_bare = 'n=' . $authcid . ',r=' . $this->cnonce;
return $this->gs2_header . $this->first_message_bare;
}
/**
* Parses and verifies a non-empty SCRAM challenge.
*
* @param string $challenge The SCRAM challenge
* @return string|false The response to send; false in case of wrong challenge or if an initial response has not
* been generated first.
* @access private
*/
private function _generateResponse($challenge, $password)
{
// XXX: as I don't support mandatory extension, I would fail on them.
// And I simply ignore any optional extension.
$server_message_regexp = "#^r=([\x21-\x2B\x2D-\x7E]+),s=((?:[A-Za-z0-9/+]{4})*(?:[A-Za-z0-9]{3}=|[A-Xa-z0-9]{2}==)?),i=([0-9]*)(,[A-Za-z]=[^,])*$#";
if (!isset($this->cnonce, $this->gs2_header)
|| !preg_match($server_message_regexp, $challenge, $matches))
{
return false;
}
$nonce = $matches[1];
$salt = base64_decode($matches[2]);
if (!$salt)
{
// Invalid Base64.
return false;
}
$i = intval($matches[3]);
$cnonce = substr($nonce, 0, strlen($this->cnonce));
if ($cnonce <> $this->cnonce)
{
// Invalid challenge! Are we under attack?
return false;
}
$channel_binding = 'c=' . base64_encode($this->gs2_header); // TODO: support channel binding.
$final_message = $channel_binding . ',r=' . $nonce; // XXX: no extension.
// TODO: $password = $this->normalize($password); // SASLprep profile of stringprep.
$saltedPassword = $this->hi($password, $salt, $i);
$this->saltedPassword = $saltedPassword;
$clientKey = call_user_func($this->hmac, $saltedPassword, "Client Key", TRUE);
$storedKey = call_user_func($this->hash, $clientKey, TRUE);
$authMessage = $this->first_message_bare . ',' . $challenge . ',' . $final_message;
$this->authMessage = $authMessage;
$clientSignature = call_user_func($this->hmac, $storedKey, $authMessage, TRUE);
$clientProof = $clientKey ^ $clientSignature;
$proof = ',p=' . base64_encode($clientProof);
return $final_message . $proof;
}
/**
* SCRAM has also a server verification step. On a successful outcome, it will send additional data which must
* absolutely be checked against this function. If this fails, the entity which we are communicating with is probably
* not the server as it has not access to your ServerKey.
*
* @param string $data The additional data sent along a successful outcome.
* @return bool Whether the server has been authenticated.
* If false, the client must close the connection and consider to be under a MITM attack.
* @access public
*/
public function processOutcome($data)
{
$verifier_regexp = '#^v=((?:[A-Za-z0-9/+]{4})*(?:[A-Za-z0-9]{3}=|[A-Xa-z0-9]{2}==)?)$#';
if (!isset($this->saltedPassword, $this->authMessage)
|| !preg_match($verifier_regexp, $data, $matches))
{
// This cannot be an outcome, you never sent the challenge's response.
return false;
}
$verifier = $matches[1];
$proposed_serverSignature = base64_decode($verifier);
$serverKey = call_user_func($this->hmac, $this->saltedPassword, "Server Key", true);
$serverSignature = call_user_func($this->hmac, $serverKey, $this->authMessage, TRUE);
return ($proposed_serverSignature === $serverSignature);
}
/**
* Hi() call, which is essentially PBKDF2 (RFC-2898) with HMAC-H() as the pseudorandom function.
*
* @param string $str The string to hash.
* @param string $hash The hash value.
* @param int $i The iteration count.
* @access private
*/
private function hi($str, $salt, $i)
{
$int1 = "\0\0\0\1";
$ui = call_user_func($this->hmac, $str, $salt . $int1, true);
$result = $ui;
for ($k = 1; $k < $i; $k++)
{
$ui = call_user_func($this->hmac, $str, $ui, true);
$result = $result ^ $ui;
}
return $result;
}
/**
* Creates the client nonce for the response
*
* @return string The cnonce value
* @access private
* @author Richard Heyes <richard@php.net>
*/
private function _getCnonce()
{
// TODO: I reused the nonce function from the DigestMD5 class.
// I should probably make this a protected function in Common.
if (@file_exists('/dev/urandom') && $fd = @fopen('/dev/urandom', 'r')) {
return base64_encode(fread($fd, 32));
} elseif (@file_exists('/dev/random') && $fd = @fopen('/dev/random', 'r')) {
return base64_encode(fread($fd, 32));
} else {
$str = '';
for ($i=0; $i<32; $i++) {
$str .= chr(mt_rand(0, 255));
}
return base64_encode($str);
}
}
}
?>
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