Secure key generation using a chaotic oscillator

A communication device and method are provided for communicating data, such as a cryptographic key, wirelessly to another communication device. The communication device and the other device each include an oscillator circuit portion, an inverter, a non-inverting buffer, and a switch for switching between the inverter and non-inverting buffer. A circular loop is formed wirelessly between the oscillator circuit portions of both devices by placing both communication devices near each other. A control circuit in each device measures a parameter such as frequency or waveform pattern of the circulating signal to determine how to position the switches. The oscillator circuit portions may be portions of the same oscillator distributed between the devices, such as a delay line-controlled oscillator or a chaotic oscillator. Inverting and not inverting the circulated signal changes the parameter of the signal so that it is difficult for an eavesdropper to learn the communication.