function login() {
    var loginForm = document.getElementById("loginForm");
    if (loginForm.username.value == "") {
        alert("Please enter your user name.");
        return false;
    }
    if (loginForm.password.value == "") {
        alert("Please enter your password.");
        return false;
    }
    var submitForm = document.getElementById("submitForm");
    submitForm.username.value = loginForm.username.value;
    submitForm.response.value =
        hex_md5(loginForm.challenge.value+loginForm.password.value);
    submitForm.submit();
    return true;
}