The embodiments provide a cryptography key for two communicating devices that is based on information known only to the devices. Each of the communicating devices determines the information without communicating key information related to the encryption key with the other. Each device receives a setup signal sent by the other device. Each device samples the received signal, generates sampling results, creates a plurality of keys based on the sampling results, selects a key of the plurality of keys based on criteria, and utilizes the selected key. The sets of plurality of keys may be created by creating each of the keys based on a different power threshold applied to the sampling results. The sets of plurality of keys may also be created by inputting the sampling results into each of a plurality of decoders to generate a key at each decoder that comprises a key of the plurality of keys.