Siaw-Lynn Ng

Threshold Anonymous Announcement in VANETs

Vehicular ad hoc networks (VANETs) allow wireless communications between vehicles without the aid of a central server. Reliable exchanges of information about road and traffic conditions allow a safer and more comfortable travelling environment. However, such profusion of information may allow unscrupulous parties to violate user privacy. On the other hand, a degree of auditability is desired for law enforcement and maintenance purposes. In this paper we propose a Threshold Anonymous Announcement service using direct anonymous attestation and one-time anonymous authentication to simultaneously achieve the seemingly contradictory goals of reliability, privacy and auditability.

A Reputation-Based Announcement Scheme for VANETs

Vehicular ad hoc networks (VANETs) allow vehicles to generate and broadcast messages to inform nearby vehicles about road conditions, such as traffic congestion and accidents. Neighboring vehicles can utilize this information, which may improve road safety and traffic efficiency. However, messages generated by vehicles may not be reliable. We propose a novel announcement scheme for VANETs based on a reputation system that allows evaluation of message reliability. We present a secure and efficient scheme that is robust and fault tolerant against temporary unavailability of the central server.

On the Composition of Matroids and Ideal Secret Sharing Schemes

In an ideal secret sharing scheme, the access structure is uniquely determined by its minimal sets Δs. The purpose of this paper is to characterise Δs. We introduce the concept of strong connectivity and show that under this equivalence relation, an ideal secret sharing scheme decomposes into threshold schemes. We also give a description of the minimal sets that span the strong connectivity classes. As a result we obtain a necessary condition on the types of subsets that are allowed in an ideal access structure as well as an upper bound on the number of such access structures.

A Representation of a Family of Secret Sharing Matroids

Deciding whether a matroid is secret sharing or not is a well-known open problem. In Ng and Walker [6] it was shown that a matroid decomposes into uniform matroids under strong connectivity. The question then becomes as follows: when is a matroid m with N uniform components secret sharing? When N = 1, m corresponds to a uniform matroid and hence is secret sharing. In this paper we show, by constructing a representation using projective geometry, that all connected matroids with two uniform components are secret sharing

Comments on "Dynamic participation in a secure conference scheme for mobile communications"

In the original paper by M.-S. Hwang (IEEE Trans. Veh. Technol., vol.48, p.1469-74, 1999), a conference scheme was proposed for providing dynamic participation. We show that this scheme is not secure against eavesdropping and impersonation.

Comments on “Proving Reliability of Anonymous Information in VANETs” by Kounga

Three vehicle-to-vehicle communication schemes by Kounga (?Proving reliability of anonymous information in VANETs,? IEEE Trans. Veh. Technol., vol. 58, no. 6, pp. 2977-2989, Jul. 2009) were recently published to address the issues of certificate management, scalability, and privacy. We present a number of attacks on one of the schemes. Our result shows that, contrary to what is claimed, this scheme does not provide the following four security features: (1) authenticity of a message; (2) privacy of drivers and vehicles; (3) reliability of distributed information; and (4) revocation of illegitimate vehicles.

Broadcast-Enhanced Key Predistribution Schemes

We present a formalisation of a category of schemes that we refer to as broadcast-enhanced key predistribution schemes (BEKPSs). These schemes are suitable for networks with access to a trusted base station and an authenticated broadcast channel. We demonstrate that the access to these extra resources allows for the creation of BEKPSs with advantages over key predistribution schemes such as flexibility and more efficient revocation. There are many possible ways to implement BEKPSs, and we propose a framework for describing and analysing them. In their paper “From Key Predistribution to Key Redistribution,” Cichoń et al. [2010] propose a scheme for “redistributing” keys to a wireless sensor network using a broadcast channel after an initial key predistribution. We classify this as a BEKPS and analyse it in that context. We provide simpler proofs of some results from their paper, give a precise analysis of the resilience of their scheme, and discuss possible modifications. We then study two scenarios where BEKPSs may be particularly desirable and propose a suitable family of BEKPSs for each case. We demonstrate that they are practical and efficient to implement, and our analysis shows their effectiveness in achieving suitable trade-offs between the conflicting priorities in resource-constrained networks.

A privacy-aware reputation-based announcement scheme for VANETs

An announcement scheme is a system that facilitates vehicles to broadcast road-related information in vehicular ad hoc networks (VANETs) in order to improve road safety and efficiency. In this paper, we propose a privacy-aware reputation-based announcement scheme that provides message reliability evaluation, auditability, and robustness.

Disjoint difference families and their applications

Difference sets and their generalisations to difference families arise from the study of designs and many other applications. Here we give a brief survey of some of these applications, noting in particular the diverse definitions of difference families and the variations in priorities in constructions. We propose a definition of disjoint difference families that encompasses these variations and allows a comparison of the similarities and disparities. We then focus on two constructions of disjoint difference families arising from frequency hopping sequences and show that they are in fact the same. We conclude with a discussion of the notion of equivalence for frequency hopping sequences and for disjoint difference families.

A certificateless anonymous authenticated announcement scheme in vehicular ad hoc networks

Vehicular ad hoc networks provide a safer driving environment by allowing vehicles to broadcast safety related messages and inform neighbouring vehicles regarding traffic and road conditions. Safety can only be achieved if transmission of messages is reliable. However, verification of reliability may violate privacy. On the other hand, it is desirable that malicious or defective vehicles can be identified and revoked. In this paper, we propose a new protocol by using certificateless signature and reputation system to achieve the sometimes contradictory requirements of a reliable, private and accountable vehicular ad hoc network message announcement scheme. Copyright