Pervasive Social Networks of Strangers are available constantly, connecting users directly with no preexisting relationships. Such networks demand a high level of privacy, as users should be anonymous and their behaviour unlinkable. However, the anonymity of users could lead to abusive messages, spam, or fraud. A possible solution is to keep track of users' reputations, based on feedback from other users. However, the need to collate feedback on user behaviour to form reputations is at odds with the need for privacy. Anonymous and unlinkable feedback is also required, whilst multiple feedbacks given on the same item should be detected. To resolve this, we use group signatures and direct anonymous attestation, to give a reputation-based messaging scheme.

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. Here, the authors propose a new cryptographic primitive for public updating of reputation score based on the Boneh–Boyen–Shacham short group signature scheme. This allows private reputation score retrieval without a secure channel. Using this, the authors devise a privacy‐aware announcement scheme using reputation systems which is reliable, auditable, and robust.

Cloud computing provides elastic, on-demand, self-provisioning computing resources to users. Highly dynamic and heterogeneous environments present significant challenges to access control. Attribute-based signature (ABS) enables fine grained access control over an expressive access policy (predicate). However, user revocation, especially anonymous user revocation, is not straightforward to provide for existing ABS schemes. In this paper we propose an anonymous revocation feature for an ABS scheme that is practical to deploy in a cloud environment.

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 reputation system is a common approach to induce sellers' good conduct in an e-marketplace, where feedback about a seller will be used by a potential future buyer to decide whether to conduct a transaction with the seller. However, reputation systems suffer from some inherent problems. We propose a novel approach that changes the fundamental role of feedback - the impact of feedback is exerted only to the transaction that the feedback is obtained from, but not future transactions. Consequently, some inherent problems of reputation systems no longer apply in our scheme. Our approach thus offers an alternative to traditional reputation systems, to induce sellers' good conduct.

Cloud storage provides the potential for on-demand massive data storage, but its highly dynamic and heterogeneous environment presents significant data protection challenges. Ciphertext-policy attribute-based encryption (CP-ABE) enables fine-grained access control. However, important issues such as efficient user revocation and key refreshing are not straightforward, which constrains the adoption of CP-ABE in cloud storage systems. In this paper we propose a dynamic user revocation and key refreshing model for CP-ABE schemes. A key feature of our model is its generic possibility in general CP-ABE schemes to refresh the system keys or remove the access from a user without issuing new keys to other users or re-encrypting existing ciphertexts. Our model is efficient and suitable for application in cloud storage environments. As an example, we use BSW's CP-ABE scheme to show the adaptation of our model to a CP-ABE scheme.

Electronic marketplaces are not always easily regulated using traditional legal systems. As a result, suitable dispute prevention and resolution mechanisms for electronic marketplaces are of interest to design. In this paper, we design a multiagent-based e-marketplace where participants represented by autonomous software agents may be egocentric, strategic and even malicious. Our marketplace focuses on trading arbitrable and replicatable services, such as computational resources and data storage, over the Internet. We propose a novel dispute prevention and resolution mechanism that is theoretically proven to be able to induce good conduct for marketplace participants. Our marketplace also features cost-effectiveness, robustness and budget balance.

Grid computing enables heterogeneous machines to share computational resources across different organisations and various geographic locations. Introducing a market-like mechanism into Grid computing benefits participants. In this paper, we propose a cost-effective and secure marketplace which encourages good conduct for Grid computing.

A two-dimensional (2-D) grid with dots is called aconfiguration with distinct differencesif any two lines which connect two dots are distinct either in their length or in their slope. These configurations are known to have many applications such as radar, sonar, physical alignment, and time-position synchronization. Rather than restricting dots to lie in a square or rectangle, as previously studied, we restrict the maximum distance between dots of the configuration; the motivation for this is a new application of such configurations to key distribution in wireless sensor networks. We consider configurations in the hexagonal grid as well as in the traditional square grid, with distances measured both in the Euclidean metric, and in the Manhattan or hexagonal metrics. We note that these configurations are confined inside maximal anticodes in the corresponding grid. We classify maximal anticodes for each diameter in each grid. We present upper bounds on the number of dots in a pattern with distinct differences contained in these maximal anticodes. Our bounds settle (in the negative) a question of Golomb and Taylor on the existence of honeycomb arrays of arbitrarily large size. We present constructions and lower bounds on the number of dots in configurations with distinct differences contained in various 2-D shapes (such as anticodes) by considering periodic configurations with distinct differences in the square grid.

A distinct difference configuration is a set of points in$\BBZ ^{2}$with the property that the vectors (difference vectors) connecting any two of the points are all distinct. Many specific examples of these configurations have been previously studied: the class of distinct difference configurations includes both Costas arrays and sonar sequences, for example. Motivated by an application of these structures in key predistribution for wireless sensor networks, we define the$k$-hop coverage of a distinct difference configuration to be the number of distinct vectors that can be expressed as the sum of$k$or fewer difference vectors. This is an important parameter when distinct difference configurations are used in the wireless sensor application, as this parameter describes the density of nodes that can be reached by a short secure path in the network. We provide upper and lower bounds for the$k$-hop coverage of a distinct difference configuration with$m$points, and exploit a connection with$B_{h}$sequences to construct configurations with maximal$k$-hop coverage. We also construct distinct difference configurations that enable all small vectors to be expressed as the sum of two of the difference vectors of the configuration, an important task for local secure connectivity in the application.

Recent literature contains proposals for key predistribution schemes for sensor networks in which nodes are deployed in separate groups. In this article we consider the implications of group deployment for the connectivity and resilience of a key predistribution scheme. We propose a flexible scheme, based on the structure of a resolvable transversal design. We demonstrate that this scheme permits effective trade-offs between resilience, connectivity and storage requirements within a group-deployed environment as compared with other schemes in the literature, and show that group deployment can be used to increase network connectivity, without increasing storage requirements or sacrificing resilience.

We propose a framework for the design and analysis of asymmetric fingerprinting protocols. By fitting existing approaches within this framework, we are able to highlight strategic differences in design techniques. We then illustrate how the framework can be used to derive new models, which in turn lead to asymmetric fingerprinting schemes with new properties.

A key assignment scheme is a cryptographic technique for implementing an information flow policy, sometimes known as hierarchical access control. All the research to date on key assignment schemes has focused on particular encryption techniques rather than an analysis of what features are required of such a scheme. To remedy this we propose a family of generic key assignment schemes and compare their respective advantages. We note that every scheme in the literature is simply an instance of one of our generic schemes. We then conduct an analysis of the Aki-Taylor scheme and propose a number of improvements. We also demonstrate that many of the criticisms that have been made of this scheme in respect of key updates are unfounded, finally, exploiting the deeper understanding we have acquired of key assignment schemes, we introduce a technique for exploiting the respective advantages of different schemes.

Threshold schemes allow secret data to be protected among a set of participants in such a way that only a prespecified threshold of participants can reconstruct the secret from private information (shares) distributed to them on a system setup using secure channels. We consider the general problem of designing unconditionally secure threshold schemes whose defining parameters (the threshold and the number of participants) can later be changed by using only public channel broadcast messages. In this paper, we are interested in the efficiency of such threshold schemes, and seek to minimize storage costs (size of shares) as well as optimize performance in low-bandwidth environments by minimizing the size of necessary broadcast messages. We prove a number of lower bounds on the smallest size of broadcast message necessary to make general changes to the parameters of a threshold scheme in which each participant already holds shares of minimal size. We establish the tightness of these bounds by demonstrating optimal schemes.

We consider the problem of redistributing shares in a secret sharing scheme in such a way that shareholders of a scheme with one access structure can transfer information to a new set of shareholders, resulting in a sharing of the old secret among a new access structure. We describe a number of different scenarios and applications within which such a redistribution might be required, give some techniques for conducting a redistribution, and discuss the optimisation of the efficiency of such a process.

Key recovery systems suitable for application among multiple domains, such as those operating within international communication networks, are investigated. A general framework for analysis of key recovery systems is introduced and a set of parameter