I'm assuming that this is related to the Digi RealPort driver?
From my own testing, TLS v1.0 128-bit AES appears to be the default encryption type, but I'm not sure if that can be changed (and to what, if so).
It's easy to enable encrypted RealPort, just select the encrypt option when installing the RealPort driver (when going through the RealPort driver setup wizard), or it can be changed later in the RealPort properties. You also need to make sure the ConnectPort TS has the Encrypted RealPort service enabled.
Is this the kind of information you're looking for?