Quantum Tagging: Authenticating Location via Quantum Information and Relativistic Signalling Constraints

TL;DR

This paper introduces quantum tagging, a method for verifying a device’s location using quantum signals, discusses security challenges, and reviews the history and insecurity of existing protocols.

Contribution

It formalizes the quantum tagging task, analyzes security pitfalls, and reviews the history and insecurity of prior protocols, highlighting the need for secure solutions.

Findings

Naive quantum cryptography protocols can be broken by teleportation attacks.

Some protocols resist teleportation-based attacks but lack proof of unconditional security.

All recent protocols are either insecure or unproven in security.

Abstract

We define the task of {\it quantum tagging}, that is, authenticating the classical location of a classical tagging device by sending and receiving quantum signals from suitably located distant sites, in an environment controlled by an adversary whose quantum information processing and transmitting power is unbounded. We define simple security models for this task and briefly discuss alternatives. We illustrate the pitfalls of naive quantum cryptographic reasoning in this context by describing several protocols which at first sight appear unconditionally secure but which, as we show, can in fact be broken by teleportation-based attacks. We also describe some protocols which cannot be broken by these specific attacks, but do not prove they are unconditionally secure. We review the history of quantum tagging protocols, which we first discussed in 2002 and described in a 2006 patent (for an insecure protocol). The possibility has recently been reconsidered by other authors. All the more recently discussed protocols of which we are aware were either previously considered by us in 2002-3 or are variants of schemes then considered, and all are provably insecure.