  Encryption for channel modulation techniques on a physical basis is
considered. A channel modulation scheme is proposed in which the selected
channel depends on both transmitter and receiver configuration. The planned
selections of the receiver become the encryption key. The communication system
is prototyped in an anechoic chamber, where channels are distinguished based on
phase differences. It is explored that, as the data is transmitted solely
through the selection of the channel, the receiver could transmit the pilot
signals and the transmitter could remain passive, i.e. the transmitter does not
transmit electromagnetic waves.
