Physical-Layer Security: Combining Error Control Coding and Cryptography

TL;DR

This paper demonstrates how combining error control coding with cryptography in the physical layer can significantly enhance security against passive eavesdroppers by increasing the complexity of cryptanalysis in wiretap channels.

Contribution

It introduces a method to strengthen cryptographic security by exploiting physical layer properties in wiretap channels, particularly for LFSR-based keystream generators.

Findings

Security of LFSR-based cryptography can be improved using physical layer properties.

Eavesdroppers face increased difficulty in cracking cryptographic keys due to channel errors.

The approach increases the computational complexity of correlation attacks.

Abstract

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.