In the virtual world of networked electronic services, finding the physical location of a device, or determining the properties of the link between two devices, might be as important as knowing their identities. Consider, for example, a sensor whose role is counting traffic at some location, or the link between a proximity card and its reader. Moreover, since there is no compulsion to believe a device (called prover), its location should be independently computable, possibly by its neighbors (called verifiers). The goal of this work is to develop a set of techniques for merging the concepts of identity authentication with either location authentication or adjacency authentication into a single peer-to-peer protocol.