A virtual wiretap channel for secure message transmission

Abstract

In the Wyner wiretap channel a sender is connected to a receiver and an eavesdropper through two noisy channels. It has been shown that if the noise in the eavesdropper channel is higher than the receiver’s channel, information theoretically secure communication from Alice to Bob, without requiring a shared key, is possible. The approach is particularly attractive noting the rise of quantum computers and possibility of the complete collapse of todays’ cryptographic infrastructure. If the eavesdropper’s channel is noise free however, no secrecy can be obtained. The iJam protocol, proposed by Gollakota and Katabi, is an interactive protocol over noise free channels that uses friendly jamming by the receiver to establish an information theoretically secure shared key between the sender and the receiver. The protocol relies on the Basic iJam Transmission protocol (BiT protocol) that uses properties of OFDM (Orthogonal Frequency-Division Multiplexing) to create uncertainty for Eve (hence noisy view) in receiving the sent information, and use this uncertainty to construct a secure key agreement protocol. The protocol has been implemented and evaluated using extensive experiments that examines the best eavesdropper’s reception strategy. In this paper we develop an abstract model for BiT protocol as a wiretap channel and refer to it as a virtual wiretap channel. We estimate parameters of this virtual wiretap channel, derive the secrecy capacity of this channel, and design a secure message transmission protocol with provable semantic security using the channel. Our analysis and protocol gives a physical layer security protocol, with provable security, that is implementable in practice (BiT protocol has already been implemented).