Optimal Grassmann Manifold Eavesdropping: A Huge Security Disaster for M-1-2 Wiretap Channels

TL;DR

This paper reveals that an advanced eavesdropper using Grassmann manifold filtering can completely nullify the secrecy rate in M-1-2 Gaussian MISO wiretap channels, posing a serious security threat.

Contribution

It introduces an optimal Grassmann manifold filtering strategy that can reduce the secrecy rate to zero, highlighting a critical security vulnerability.

Findings

Optimal filters form a complex Grassmann manifold.

Secrecy rate can be reduced to zero with the proposed eavesdropper.

Numerical results demonstrate the severe security risk.

Abstract

We in this paper introduce an advanced eavesdropper that aims to paralyze the artificial-noise-aided secure communications. We consider the M-1-2 Gaussian MISO wiretap channel, which consists of a M-antenna transmitter, a single-antenna receiver, and a two-antenna eavesdropper. This type of eavesdropper, by adopting an optimal Grassmann manifold (OGM) filtering structure, can reduce the maximum achievable secrecy rate (MASR) to be zero by using only two receive antennas, regardless of the number of antennas at the transmitter. Specifically, the eavesdropper exploits linear filters to serially recover the legitimate information symbols and intends to find the optimal filter that minimizes the meansquare error (MSE) in estimating the symbols. During the process, a convex semidefinite programming (SDP) problem with constraints on the filter matrix can be formulated and solved. Interestingly, the resulted optimal filters constitute a complex Grassmann manifold on the matrix space. Based on the filters, a novel expression of MASR is derived and further verified to be zero under the noiseless environment. Besides this, an achievable variable region (AVR) that induces zero MASR is presented analytically in the noisy case. Numerical results are provided to illustrate the huge disaster in the respect of secrecy rate.