You can also pot the PCB, and/or enclose it in a physically secure enclave where if it detects ambient light, actuation of a switch, breach of a conductive trac

You can also pot the PCB, and/or enclose it in a physically secure enclave where if it detects ambient light, actuation of a switch, breach of a conductive trace embedded in the case around it, etc, it wipes the RAM and, depending on your paranoia levels, blows the hardware up. Some key management Hardware Security Modules do this. Also this: https://en.wikipedia.org/wiki/Harvey's_Resort_Hotel_bombing https://en.wikipedia.org/wiki/Harvey's_Resort_Hotel_bombing The designer could probably have made more cash patenting his systems!