The embodiments provide cryptography that is performed in each of two communicating devices and is based on information known only to the devices. The information is determined in each of the devices at the time of communications. Each of the devices determines the information without communicating key information related to the encryption key with each other. Channel characteristic reciprocity between the two devices allows creation of identical keys in each device. Each of the devices sends a first setup signal to the other device, receives a second setup signal from the other device, where the second setup signal may be a looped back version of the first setup signal, samples the second setup signal, generates sampling results, creates a key based on the sampling results, and utilizes the key to exchange one or more secure data signals with the other device.