1. Easy route: uC, which is an obvious chip that you must have + DS2401 (silicon serial number)
2. Harder route: uC + DS1991, or uC + SRAM
In both routes, some encryption or "play" with data from Dallas-Maxim or SRAM has to be done.
In my career I've reverse engineered some PCB's, not for "just being a copycat" but bacause manufacturers being "belly up - out of business).
In one particular design with uC, I made a complication for potential copycats. They did send a uC to ic-break, got the .hex file and spent over two years trying to figure out how to reproduce the device, and finally they gave up. They made they own software and hardware. It was cheaper :smile:.