Covert Communications through Imperfect Cancellation

What is it about?

The term covert communications may elicit assumptions of nefarious purposes. It is true that covert communications can be used for exfiltration and other exploits; but these covert communications can also be a force for good, such as providing a means of message authentication to prevent malicious actors from spoofing networks. It is not unreasonable to expect privacy. What are the consequences of all of your signals being intercepted? What information can be extracted despite encryption? Consider signals from a medical device. RF Fingerprinting can reveal what type of device you have, violating your privacy, direction-finding can be used on the emissions from your medical device thus violating your security, and these things can be done without ever trying to crack encryption. Covert communications changes this paradigm by providing a defense against signal interception in the first place.

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Photo by Marija Zaric on Unsplash

Photo by Marija Zaric on Unsplash

Why is it important?

This paper describes how a covert signal can be hidden inside and recovered from within the bandwidth of a Wi-Fi signal. The process of recovering the hidden signal is detailed, and measurements are taken on the impact and performance of the covert signal. The contributions of this work are: 1) The design of a covert signal to be hidden in a Wi-Fi signal; 2) Test of the impact of this covert signal on the Wi-Fi signal; 3) A detailed OFDM cancellation scheme designed to maintain white noise for the covert receiver; 4) Test of the detectability of this covert signal; 5) Application of this cancellation scheme on Wi-Fi using both synthetic and Over-the-Air data.

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