function signature ( $request, $base_string, $consumer_secret, $token_secret )
	{
		$s  .= '&'.$request->urlencode($consumer_secret).'&'.$request->urlencode($token_secret);
		$md5 = md5($base_string);
		$bin = '';
		
		for ($i = 0; $i < strlen($md5); $i += 2)
		{
		    $bin .= chr(hexdec($md5{$i+1}) + hexdec($md5{$i}) * 16);
		}
		return $request->urlencode(base64_encode($bin));
	}