Privacy-Preserving Proof-of-Location With Security Against Geo-Tampering

Abstract

A Proof-of-Location (POL) system is used to issue a proof-of-location token ( <inline-formula><tex-math notation="LaTeX">$pol$</tex-math></inline-formula> ) to a user who has been present at a location <inline-formula><tex-math notation="LaTeX">$\ell oc$</tex-math></inline-formula> , such that it can be later presented to a verifier to assure the presence of the user at <inline-formula><tex-math notation="LaTeX">$\ell oc$</tex-math></inline-formula> . Basic POL security requirements are <i>unforgeability</i> of <inline-formula><tex-math notation="LaTeX">$pol$</tex-math></inline-formula> , and its <i>non-transferability</i> (a <inline-formula><tex-math notation="LaTeX">$pol$</tex-math></inline-formula> issued to user <inline-formula><tex-math notation="LaTeX">$u_1$</tex-math></inline-formula> cannot be used by <inline-formula><tex-math notation="LaTeX">$u_2$</tex-math></inline-formula> ). An additional important property of POL systems is <i>user privacy</i> against the issuers and verifiers. We make two contributions. First, we formalize the POL security and privacy properties, and construct the first system providing provable security and privacy against the issuer and the verifier, both. Second, we introduce a <i>geo-tampering attack</i> that completely breaks POL system security, by simply changing the location of a <inline-formula><tex-math notation="LaTeX">$pol$</tex-math></inline-formula> issuing node. The attack applies to portable infrastructure nodes that are not continually monitored. We propose an algorithm that is used by a <inline-formula><tex-math notation="LaTeX">$pol$</tex-math></inline-formula> issuer to provide a location integrity “proof”, that will be embedded in a <inline-formula><tex-math notation="LaTeX">$pol$</tex-math></inline-formula> to protect against this attack. The proof relies on a novel application of euclidean Distance Matrices. We implemented our POL on an off-the-shelf Android smartphone to show the practicality of the proposed algorithms.