public String genericAppCodeKey(int minorVersion, int majorVersion, String userName) {
    BigInteger pubKey = new BigInteger(
        "F0DD6995C4BD3223641C79C8608D74F32ED54A8BDAE468EB5AC53F1F1C8925E263F82317356BC73B1C82B520630250212416C99CB39A8B7C2611E35552E166B9",
        16);
    BigInteger privKey = new BigInteger(