Unshared Secret Key Cryptography

TL;DR

This paper introduces the unshared secret key (USK) cryptosystem for MIMO wiretap channels, which uses artificial noise as a one-time pad aligned in the null space, providing perfect secrecy without key exchange.

Contribution

It proposes a novel physical layer cryptographic scheme combining network and physical layer security, achieving Shannon's ideal secrecy with finite constellations.

Findings

USK guarantees Shannon's ideal secrecy and perfect secrecy.

The scheme works for infinite and finite lattice input alphabets.

Outage probability can be made arbitrarily small.

Abstract

Current security techniques can be implemented with either secret key exchange or physical layer wiretap codes. In this work, we investigate an alternative solution for MIMO wiretap channels. Inspired by the artificial noise (AN) technique, we propose the unshared secret key (USK) cryptosystem, where the AN is redesigned as a one-time pad secret key aligned within the null space between transmitter and legitimate receiver. The proposed USK cryptosystem is a new physical layer cryptographic scheme, obtained by combining traditional network layer cryptography and physical layer security. Unlike previously studied artificial noise techniques, rather than ensuring non-zero secrecy capacity, the USK is valid for an infinite lattice input alphabet and guarantees Shannon's ideal secrecy and perfect secrecy, without the need of secret key exchange. We then show how ideal secrecy can be obtained for finite lattice constellations with an arbitrarily small outage.