Position Based Cryptography

Abstract

We consider what constitutes identities in cryptography. Typical examples include your name and your social-security number, or your fingerprint/iris-scan, or your address, or your (non-revoked) publickey coming from some trusted public-key infrastructure. In many situations, however, where you are defines your identity. For example, we know the role of a bank-teller behind a bullet-proof bank window not because she shows us her credentials but by merely knowing her location. In this paper, we initiate the study of cryptographic protocols where the identity (or other credentials and inputs) of a party are derived from its geographic location.We start by considering the central task in this setting, i.e., securely verifying the position of a device. Despite much work in this area, we show that in the Vanilla (or standard) model, the above task (i.e., of secure positioning) is impossible to achieve. In light of the above impossibility result, we then turn to the Bounded Storage Model and formalize and construct information theoretically secure protocols for two fundamental tasks:-Secure Positioning; and -Position Based Key Exchange.We then show that these tasks are in fact universal in this setting -we show how we can use them to realize Secure Multi-Party Computation. Our main contribution in this paper is threefold: to place the problem of secure positioning on a sound theoretical footing; to prove a strong impossibility result that simultaneously shows the insecurity of previous attempts at the problem; and to present positive results by showing that the bounded-storage framework is, in fact, one of the "right" frameworks (there may be others) to study the foundations of position-based cryptography.Full version available on eprint.

Practical position-based quantum cryptography

“…In the literature, this family is often considered in the single qubit case, for instance with U = {id, H} where H is the Hadamard gate [1,9,16]. Then it makes sense to repeat the protocol n times in order to build some statistics.…”

“…Position verification protocols have been studied in the classical setting where the challenges are described by classical information, and it was shown in [1] that information-theoretic security could never be obtained in the standard (Vanilla) model. More precisely, it is always possible for a coalition of adversaries to convince the verifiers, even if none of the adversaries sits in the spatio-temporal region where the prover is supposed to be.…”

LINK: Location Verification through Immediate Neighbors Knowledge

“…To the best of our knowledge, all existing solutions employ trusted network/localization infrastructure [3,4,10,11,12,13,14] to detect malicious users claiming false locations. Most of these solutions use distance bounding techniques, in which a beacon acting as verifier challenges the mobile device and measures the elapsed time until the receipt of its response.…”

A Formal Approach to Distance-Bounding RFID Protocols

“…Most prominently, the recent position-based cryptography work [14] aims to determine if a prover is (exactly) at a claimed position -but in a single protocol run, with many verifiers. This is clearly different from Mafia fraud or terrorist fraud attacks.…”

“…This is clearly different from Mafia fraud or terrorist fraud attacks. As adversaries in [14] must all have the same knowledge as the prover (also knowledge of the private key), this model is closest to our distance fraud model, where tags must prove they are closer to the reader than they really are. However, exact positioning is impossible in practice for RFID, requiring too many readers to deal with the high variance in response time.…”