This project develops techniques to provide information-theoretic secrecy for messages transmitted in a wireless communication system for the challenging scenario where an eavesdropper receives a stronger signal than the desired recipient: for example, the eavesdropper might be significantly closer to the transmitter than the intended receiver. The approach considered in this project starts with the transmitter and intended receiver sharing an ephemeral cryptographic key, which the transmitter then employs to intentionally distort the transmitted signal. With knowledge of the key, the intended receiver has a significant advantage over the eavesdropper in reducing this intentional distortion before analog-to-digital conversion and the recording of the signal. Even if the eavesdropper obtains the key at some later time, the nonlinearity of the analog-to-digital conversion and the fact that non-linear operators are not necessarily commutative implies the eavesdropper cannot remove the intentional distortion. In this manner, information-theoretic secrecy is obtained. The project will consider methods of maximizing the rate of secret communications through this technique. First, approaches to narrowband systems that employ an additive jamming signal based on the shared key will be developed. Next, attention will turn to wideband systems, where the shared key can be used to additionally hide the band of operation of the transmitter, hence further inhibiting the eavesdropper. Critical to the consideration of wideband systems is considering broad classes of emerging receiver capabilities for the eavesdropper. Finally, the project will build on recent analytic techniques to consider the provisioning of secrecy in network scenarios where the interaction of the transmissions of different system nodes must be considered.
The protection of messages in wireless communication systems from eavesdropping has clear societal benefit. Standardly employed cryptographic approaches make critical assumptions on the current and future computational capabilities of the eavesdropper, who may record a transmitted message and attempt to break it over a long time period; hence, information-theoretic techniques are of interest for the provisioning of everlasting secrecy. However, information-theoretic secrecy generally requires an advantage for the intended recipient over the eavesdropper, which, per above, is difficult to guarantee in wireless communication systems, leading to a significant risk that the contents of a message will be immediately compromised. The technique considered here exploits the strengths of both cryptographic approaches, which are not susceptible to an eavesdropper close to the transmitter, and information-theoretic approaches, which provide everlasting secrecy if the required advantage is available for the recipient over the eavesdropper. The result is a method with the potential to provide significant broad societal benefit through a technique for robust everlasting secrecy in wireless communication systems. The project also has a significant educational theme, providing both outreach to K-12 students and significant project and research opportunities to a diverse set of University of Massachusetts students.