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IT Live Seminars

on 30-03-2007


Information-theoretic security in wireless networks: from theory to practice.

João Barros (FCUP).

March 30, 2007, Friday, 16h30m.

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 quasistatic 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. In the second part of the talk, we will propose 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 (Princeton/DCC-FCUP), Matthieu Bloch and Steve McLaughlin (Georgia Tech).

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