On Massive MIMO Physical Layer Cryptosystem

TL;DR

This paper analyzes the security of a massive MIMO physical layer cryptosystem, demonstrating vulnerabilities to zero-forcing attacks and exploring conditions under which the legitimate user maintains an advantage over eavesdroppers.

Contribution

It introduces a zero-forcing attack on SVD-based precoded massive MIMO cryptography and characterizes the advantage dynamics based on the eavesdropper's antenna count.

Findings

Eavesdropper can decrypt data under the same conditions as the legitimate receiver.

When eavesdropper has many more antennas, the advantage diminishes regardless of precoding.

Upper bound on the advantage is proportional to the square of the number of antennas, achievable with inverse precoding.

Abstract

In this paper, we present a zero-forcing (ZF) attack on the physical layer cryptography scheme based on massive multiple-input multiple-output (MIMO). The scheme uses singular value decomposition (SVD) precoder. We show that the eavesdropper can decrypt/decode the information data under the same condition as the legitimate receiver. We then study the advantage for decoding by the legitimate user over the eavesdropper in a generalized scheme using an arbitrary precoder at the transmitter. On the negative side, we show that if the eavesdropper uses a number of receive antennas much larger than the number of legitimate user antennas, then there is no advantage, independent of the precoding scheme employed at the transmitter. On the positive side, for the case where the adversary is limited to have the same number of antennas as legitimate users, we give an $\mathcal{O}\left(n^2\right)$ upper bound on the advantage and show that this bound can be approached using an inverse precoder.