Physical-Layer Security: Combining Error Control Coding and Cryptography

Harrison, Willie K
McLaughlin, Steven W.
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In this paper we consider tandem error control coding and cryptography in the setting of the {\em wiretap channel} due to Wyner. In a typical communications system a cryptographic application is run at a layer above the physical layer and assumes the channel is error free. However, in any real application the channels for friendly users and passive eavesdroppers are not error free and Wyner's wiretap model addresses this scenario. Using this model, we show the security of a common cryptographic primitive, i.e. a keystream generator based on linear feedback shift registers (LFSR), can be strengthened by exploiting properties of the physical layer. A passive eavesdropper can be made to experience greater difficulty in cracking an LFSR-based cryptographic system insomuch that the computational complexity of discovering the secret key increases by orders of magnitude, or is altogether infeasible. This result is shown for two fast correlation attacks originally presented by Meier and Staffelbach, in the context of channel errors due to the wiretap channel model.
Comment: 12 pages, 5 figures. Submitted and accepted to the International Conference on Communications (ICC) 2009. v2: equivalent to the version that will be published in the conference proceedings. Has some altered notation from version 1 as well as slight changes in the wording to make the paper more readable and easier to understand
Computer Science - Information Theory, Computer Science - Cryptography and Security, H.1.1, K.6.5