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.

A new secure authentication based distance bounding protocol

“…The concept of three verifiers was introduced by Capkun & Hubaux (2005), Shmatikov & Wang (2007), Singelee & Preneel (2005). Collision attacks were studied by Chandran et al (2014), Chiang, Haas & Hu (2009).…”

Position-Based Cryptography and Multiparty Communication Complexity

“…The standard way to identify participants in cryptographic protocols is to check their knowledge of some secret data (like a password or a key), to verify some biometric information, or the possession of some hardware tokens. A new intriguing idea, known under the name of position-based cryptography (PBC) [16] is to construct algorithms in which the participating parties are identified by their geographic position. For example, consider the setting where we want to grant access to a server only to the personnel within some military base.…”

“…Of course, such protocols can be combined with other means of authentication, and hence they can also serve for providing an additional layer of security. See [16] for more on potential applications of this concept.…”

“…, V n positioned in space and letting them jointly verify the distance from the prover. Unfortunately, as shown by Chandran et al [16], the problem of designing PBC protocols is harder than it may seem at the first sight. In fact, they show that in the so-called vanilla model (i.e.…”

“…On the other hand, the honest parties of a protocol should be only required to access small parts of X in order to complete the protocol. The way this model is used in [16] is as follows: it is assumed that there is a group of verifiers V i positioned in space. Suppose that a prover P claims to be at some position P. Each of the verifiers broadcasts a long string X i in such a way that all the X i 's arrive at P at the same time T .…”