Random numbers are a relative concept. In general, random numbers used in digital electronics are called Psuedo-Random sequences. There is a defined algorithm that is used to generate the sequence and does not actually occur in nature. In applications like Flashing a LED, this method is fine. However, for any level of encryption this is unacceptable.
Steve Buch at Electronics Weekly writes about how researchers Dr. Marie O’Neill and Dr. Jiang Wu at the University’s Institute of Electronics and Communications Information Technology (ECIT) has developed methods to generate true random bits digitally.
Fundamental to all of the ECIT generators is the effect of random noise during the transition from a metastable state to a bistable state.
Whether the output becomes a 0 or 1 depends on conditions, including internal noise, at the instant of input transition.
If you are giving thoughts to creating a cryptographic device, you might want to give their methods a look.