Matthieu Bloch
Georgia Institute of Technology



The benefits offered by ubiquitous communication networks are now mitigated by the relative ease with which malicious users can interfere or tamper with sensitive data. The past decade has thus witnessed a growing concern for the issues of privacy, confidentiality, and integrity of communications. In particular, users in a communication network now often wish to communicate without being detected by others.

In this talk, we will present a framework to analyze the fundamental limits of covert communication over noisy channels based on the concepts of source and channel resolvability. Source and channel resolvability are canonical information- theoretic problems that exploit error-control codes as a means to shape the distribution of stochastic processes. This con- ceptual approach allows us to extend prior work by developing a complete characterization of the fundamental limits of covert communications for point-to-point channels. In particular, we show that, irrespective of the quality of the channels, it is possible to communicate $O(\sqrt(n))$ reliable and covert bits over $n$ channel uses if the transmitter and the receiver share a key of size $O(\sqrt(n))$; this improves upon earlier results requiring a key of size $O(\sqrt(n)\log n)$ bits. Second, we show that, under certain conditions, it is possible to communicate $O(\sqrt(n))$ reliable and covert bits over $n$ chan- nel uses without a secret key; this generalizes an earlier result established for binary symmetric channels.

The main technical problem that we address is how to develop concentration inequalities for “low-weight” sequences; the crux of our approach is to define suitably modified typical sets that are amenable to concentration inequalities. We will
Matthieu Bloch is an Associate Professor in the School of Electrical and Computer Engineering. He received the Engi- neering degree from Supélec, Gif-sur-Yvette, France, the M.S. degree in Electrical Engineering from the Georgia Insti- tute of Technology, Atlanta, in 2003, the Ph.D. degree in Engineering Science from the Université de Franche-Comté, Besançon, France, in 2006, and the Ph.D. degree in Electrical Engineering from the Georgia Institute of Technology in 2008. In 2008-2009, he was a postdoctoral research associate at the University of Notre Dame, South Bend, IN. Since July 2009, Dr. Bloch has been on the faculty of the School of Electrical and Computer Engineering, and from 2009 to 2013 Dr. Bloch was based at Georgia Tech Lorraine. His research interests are in the areas of information theory, error- control coding, wireless communications, and cryptography. Dr. Bloch is a member of the IEEE and has served on the organizing committee of several international conferences; he was the chair of the Online Committee of the IEEE Information Theory Society from 2011 to 2014. He is the co-recipient of the IEEE Communications Society and IEEE Information Theory Society 2011 Joint Paper Award and the co-author of the textbook \emph{Physical-Layer Security: From Information Theory to Security Engineering} published by Cambridge University Press