Paper 2014/114

Prover Anonymous and Deniable Distance-Bounding Authentication

Sebastien Gambs, Cristina Onete, and Jean-Marc Robert

Abstract

In distance-bounding authentication protocols, a verifier confirms that a prover is (1) legitimate and (2) in the verifier's proximity. Proximity checking is done by running time-critical exchanges between both parties. This enables the verifier to detect relay attacks (a.k.a. mafia fraud). While most distance-bounding protocols offer resistance to mafia and distance fraud as well as to impersonation attacks, only few protect the privacy of the authenticating prover. One exception is the protocol due to Hermans, Peeters, and Onete developed in 2013, which offers strong privacy guarantees with respect to a Man-in-the-Middle adversary. However, this protocol provides no privacy guarantees for the prover with respect to a malicious verifier, who can fully identify the prover. Having in mind possible verifier corruption or data leakage from verifiers to a centralized server, we suggest that stronger privacy properties are needed. In this paper, we propose an efficient distance-bounding protocol that gives strong prover privacy guarantees even with respect to the verifier or to a centralized back-end server, storing prover information and managing revocation and registration. Specifically, we formally model and define prover anonymity, a property guaranteeing that verifiers infer only the legitimacy of the prover but not his identity, and deniability, which ensures that the back-end server cannot distinguish prover behavior from malicious verifier behavior (i.e., provers can deny that they authenticated). Finally, we present an efficient protocol that achieves these strong guarantees, give exact bounds for each of its security properties, and prove these statements formally.

Note: Protocol modification, following a comment by Serge Vaudenay, whose input we are grateful for.