Low-power Secret-key Agreement over OFDM

Information-theoretic secret-key agreement is perhaps the most practically feasible mechanism that provides unconditional security at the physical layer to date. In this paper, we consider the problem of secret-key agreement by sharing randomness at low power over an orthogonal frequency division multiplexing (OFDM) link, in the presence of an eavesdropper. The low power assumption greatly simplifies the design of the randomness sharing scheme, even in a fading channel scenario. We assess the performance of the proposed system in terms of secrecy key rate and show that a practical approach to key sharing is obtained by using low-density parity check (LDPC) codes for information reconciliation. Numerical results confirm the merits of the proposed approach as a feasible and practical solution. Moreover, the outage formulation allows to implement secret-key agreement even when only statistical knowledge of the eavesdropper channel is available.Comment: 9 pages, 4 figures; this is the authors prepared version of the paper with the same name accepted for HotWiSec 2013, the Second ACM Workshop on Hot Topics on Wireless Network Security and Privacy, Budapest, Hungary 17-19 April 201

Practical LDPC coded modulation schemes for the fading broadcast channel with confidential messages

The broadcast channel with confidential messages is a well studied scenario from the theoretical standpoint, but there is still lack of practical schemes able to achieve some fixed level of reliability and security over such a channel. In this paper, we consider a quasi-static fading channel in which both public and private messages must be sent from the transmitter to the receivers, and we aim at designing suitable coding and modulation schemes to achieve such a target. For this purpose, we adopt the error rate as a metric, by considering that reliability (security) is achieved when a sufficiently low (high) error rate is experienced at the receiving side. We show that some conditions exist on the system feasibility, and that some outage probability must be tolerated to cope with the fading nature of the channel. The proposed solution exploits low-density parity-check codes with unequal error protection, which are able to guarantee two different levels of protection against noise for the public and the private information, in conjunction with different modulation schemes for the public and the private message bits.Comment: 6 pages, 4 figures, to be presented at IEEE ICC'14 - Workshop on Wireless Physical Layer Securit