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

A Proof-of-Location (POL) system is used to issue a proof-of-location token (
$pol$
) to a user who has been present at a location
$\ell oc$
, such that it can be later presented to a verifier to assure the presence of the user at
$\ell oc$
. Basic POL security requirements are
unforgeability
of
$pol$
, and its
non-transferability
(a
$pol$
issued to user
$u_1$
cannot be used by
$u_2$
). An additional important property of POL systems is
user privacy
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
geo-tampering attack
that completely breaks POL system security, by simply changing the location of a
$pol$
issuing node. The attack applies to portable infrastructure nodes that are not continually monitored. We propose an algorithm that is used by a
$pol$
issuer to provide a location integrity “proof”, that will be embedded in a
$pol$
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.