  Unlike conventional anti-eavesdropping methods that always require additional
energy or computing resources (e.g., in friendly jamming and cryptography-based
solutions), this work proposes a novel anti-eavesdropping solution that comes
with mostly no extra power nor computing resource requirement. This is achieved
by leveraging the ambient backscatter communications in which secret
information can be transmitted by backscattering it over ambient radio signals.
Specifically, the original message at the transmitter is first encoded into two
parts: (i) active transmit message and (ii) backscatter message. The active
transmit message is then transmitted by using the conventional wireless
transmission method while the backscatter message is transmitted by
backscattering it on the active transmit signals via an ambient backscatter
tag. As the backscatter tag does not generate any active RF signals, it is
intractable for the eavesdropper to detect the backscatter message. Therefore,
secret information, e.g., secret key for decryption, can be carried by the
backscattered message, making the adversary unable to decode the original
message. Simulation results demonstrate that our proposed solution can
significantly enhance security protection for communication systems.
