HyNet Advanced Network Colloquium Series
Information-Theoretic Security in Wireless Networks: From Theory to Practice

Joao Barros
Universidade do Porto

Abstract
Recent theoretical and practical work has shown that novel physical layer security techniques have the potential to significantly strengthen the security of wireless networks. In the first part of this talk we will briefly review the fundamentals in information-theoretic security and discuss our most recent results. Formulating the problem as one in which two legitimate partners communicate over a quasistatic fading channel and an eavesdropper observes their transmissions through another independent quasi-static fading channel, we define the secrecy capacity in terms of outage probability and provide a complete characterization of the maximum transmission rate at which the eavesdropper is unable to decode any information. In sharp contrast with known results for Gaussian wiretap channels (without feedback), our results show that in the presence of fading information-theoretic security is achievable even when the eavesdropper has a better average signal-to-noise ratio (SNR) than the legitimate receiver. The role of channel state information shall be discussed in detail.

In the second part of the talk, we present a practical security scheme by which two terminals (say Alice and Bob) are able to exploit the randomness of wireless fading channels to exchange data in an information-theoretically secure way. To ensure that a potential eavesdropper (say Eve) is unable to decode any useful information, Alice sends useful symbols to Bob only when the instantaneous secrecy capacity is strictly positive. In the remaining time, a specially designed class of LDPC codes is used for reconciliation, thus allowing the extraction of a secret key, which can be distilled using privacy amplification. We believe this opportunistic approach can be used effectively as a physical layer complement to existing cryptographic protocols.

Joint work with Miguel Rodrigues, Matthieu Bloch and Steve McLaughlin.

Biography
João Barros received his undergraduate education in Electrical and Computer Engineering from the Universidade do Porto (UP), Portugal and Universitaet Karlsruhe, Germany, until 1999, and the Ph.D. degree in Electrical Engineering and Information Technology from the Technische Universitaet Muenchen (TUM), Germany, in 2004. After his doctoral research on network information theory and joint source and channel coding, João Barros joined the faculty of the Department of Computer Science at the Universidade do Porto, where he currently leads the Networking and Information Processing Group of the Instituto de Telecomunicações (a National Laboratory in Communications Engineering with more that 150 researchers with a PhD). The focus of his research lies in the general areas of information theory, communication networks and data security. In 2003, Dr. Barros received a Best Teaching Award from the Bavarian State Ministry of Sciences, Research and the Arts. In 2002 and 2003, he spent six months as a Fulbright scholar at Cornell University, where he worked on fundamental limits of wireless sensor networks. João Barros serves on the Technical Program Committees of ISIT 2007 and SSI 2006. In July 2006, he was appointed Secretary of the Board of Governors of the IEEE Information Theory Society.

Host
Prakash Narayan

The Maryland Hybrid Networks Center is a "NASA Research Partnership Center" and part of the Institute for Systems Research.

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