The Best Solution to make secure communication between two applications on the same system

I'm writing a software which is divided into two separate stand-alone pieces, one is a service like application that handles all the logics, the other one is a GUI application that just works as a front-end and is aimed to be used by the end user. The service would listen to a port and accept requests from the client(GUI) application.

since some sensitive information is exchanged between service and GUI applications, they need to be encrypted before getting transferred. one way to secure data is to use a key based encryption but keys need to be stored somewhere on the disk or even in the application's source code, but would rather avoid using keys.

now my question is that how can I handle a secure connection between service and GUI application without using a key based encryption algorithm.