UC Riverside

Time-based secure localization protocols allow a group of mutually trusted entities called verifiers to cooperatively determine the location of an untrusted and possibly malicious stranger entity called the prover. Many applications associate certain privileges with the true physical location of an entity, therefore there is an incentive for a prover to claim a more "valuable" location, different from its true location. A well known threat to time-based localization protocols is distance fraud where a malicious prover misrepresents its location by intentionally changing its response time across a series of bilateral dialogues with individual verifiers. To address this threat, secure localization protocols must use a technique called "simultaneous multilateration".

A recently introduced protocol used simultaneous challenges by multiple verifiers, over separate RF channels, to defend against distance fraud. The authors also claimed that simultaneous multilateration by using simultaneous challenges, is optimal in the sense of achieving the maximal security that can be provided by any time-based localization protocol. In the first part of this thesis, we show that the structure of this newly proposed protocol is unnecessary, and significantly more complex than existing protocols. We propose a new protocol named Elliptical Multilateration (EM) that does not use simultaneous challenges. Instead, our EM protocol achieves simultaneity in multilateration by using multiple passive receivers to observe the prover's response. Our EM protocol requires fewer resources, provides commensurate security against distance fraud, and is inherently more accurate.

The second part of this thesis focuses on the issues related to practical implementation of time-based localization protocols. Most existing works focus on cryptographic aspects of time-based secure localization protocols. We found that the existing literature does not

address the issues that arise when these time-based protocols are implemented on real systems. For example, many authors have designed protocols based on single-bit exchanges (which is non-conformant with standard networking protocols and hardware, and extremely difficult to implement), ignore inevitable measurement errors etc. In this thesis, we show that the amount and magnitude of measurement errors depend largely on the structure of a protocol, and differ significantly across the known localization protocols. We investigate whether measurements can be made with sufficient accuracy to achieve localization on the order of a few meters. To the best of our knowledge, this thesis is the first work that attempts to analyze measurement error in practical realization of different localization protocols. The factors influencing the measurement errors, which are highlighted in this thesis, are significant and cannot be ignored.

We show that taking into account the significance of message structure and the factors influencing the measurement error, can lead to new protocols that are no worse in terms of security, need fewer message exchanges, and achieve better accuracy in comparison to existing time-based localization protocols.