In some examples, a controller is configured to generate a key based on a physics-based output of a component. The controller may, for example, use the key to authenticate communication between at least two nodes, to encrypt data, or to decrypt data, may be generated based on a physics-based output generated a component. The output generated by the component may vary over time, such that the controller is configured to generate a different key, depending on the time at which the output from the component used to generate the key was generated by the component. In some examples, the key is not stored in a memory, and is a discrete signal that only exists in real-time while the component is active and generating the detectable output.