Transcript: If we want to communicate through interstellar space with intelligent civilizations, we’ll have to decide on what message we want to send and how to code it. This is highly complex. How do we turn a subtle and complicated idea into a simple set of signals or bits of information? We have to reduce complexity to simple form, ones and zeroes, on and off, light and dark. This is a difficult process. We presume that a successful SETI signal will have to be pulsed to distinguish it from cosmic noise or other astrophysical sources of radiation. We presume that a successful signal that carries meaning will have to have a pattern. In other words it is neither random, nor completely regular. A completely regular periodic signal carries only one bit of information, the frequency of the pulsed source. These are the principles, but in practice it is likely to be far easier to decide that any signal that we might receive is nonrandom than to actually decode what it means. This is one of the fundamental lessons of cryptology.