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;
var crypt_pass = hex_sha256(loginForm.password.value);
submitForm.response.value = 
hex_sha256(loginForm.challenge.value+crypt_pass);
submitForm.submit();
}