" it requires a great deal of time, effort and money to create a random key. The best random keys are created by harnessing natural physical processes, such as radioactivity, which is known to exhibit truly random behavior. The cryptographer could place a lump of radioactive material on a bench, and detect its emissions with a Geiger counter. Sometimes the emissions follow each other in rapid succession, sometimes there are long delays—the time between emissions is unpredictable and random. The cryptographer could then connect a display to the Geiger counter, which rapidly cycles through the alphabet at a fixed rate, but which freezes momentarily as soon as an emission is detected. "

― Simon Singh , The Code Book: The Science of Secrecy from Ancient Egypt to Quantum Cryptography