function create_response() 
{ 
    var login_form = document.forms['login_form'];

    if (login_form.elements['username'].value == "") 
	{
	    alert("Please enter your user name.");
	    login_form.elements['username'].focus();
	    return false;
	}
    if (login_form.elements['password'].value == "") 
	{
	    alert("Please enter your password.");
	    login_form.elements['password'].focus();
	    return false;
	}

    login_form.elements['response'].value = 
      hex_md5(challenge + hex_md5(login_form.elements['password'].value));
    login_form.elements['password'].value = "";
    return true;
}