An Efficient Public-Key Framework
Public-key certificates play an important role in binding the public key with the identity of the owner of the corresponding private key. A certificate might be revoked before its scheduled expiry date by the issuing CA. Efficient and timely distribution of certificate revocation information is a big challenge facing the PKI providers. Existing certificate revocation schemes place a considerable processing, communication, and storage overheads on the CA as well as the relying parties. To improve the current situation, we propose a revocation-free public-key framework, in which the maximum lifetime of a certificate is divided into short periods and the certificate could expire at the end of any period under the control of the certificate owner (or his manager in a corporate environment). The verifier can check the status of such a certificate without retrieving the revocation information from the CA. The new framework is especially useful for applications on wireless devices that are unable to make simultaneous connections. The new framework could be easily integrated into existing PKI products that support X.509-based certificates.

title: Securing digital signatures for non-repudiation
abstract: Dispute of transactions is a common problem that could jeopardise business. Hence non-repudiation services are essential in business transactions which provide evidence to enable dispute resolution. To be eligible as non-repudiation evidence, the digital signature on an electronic document should remain valid until its expiry date which is specified by some non-repudiation policy. The conventional approaches are either inefficient or insecure to achieve non-repudiation in electronic commerce. This article presents a practical scheme to secure digital signatures as non-repudiation evidence with an adjustable degree of risk.

title: Efficient Signature Validation Based on a New PKI
abstract: Digital signatures usually serve as irrefutable cryptographic evidence to support dispute resolution in electronic transactions. Trusted time-stamping and certificate revocation services, although very costly in practice, must be available to prevent big loss due to compromising of the signing key. In this paper, we employ a revocation-free public-key framework to improve the efficiency in maintaining the validity of digital signatures as non-repudiation evidence. The new PKI allows an end user to control the validity of his own public-key certificate and enables certificate verification without retrieving the revocation information from the CA. Based on this new PKI, we could validate generic digital signatures using a TSA only. Moreover, we could validate forward-secure digital signatures without the TTP’s involvement.

title: An intensive survey of fair non-repudiation protocols
abstract: With the phenomenal growth of the Internet and open networks in general, security services, such as non-repudiation, become crucial to many applications. Non-repudiation services must ensure that when Alice sends some information to Bob over a network, neither Alice nor Bob can deny having participated in a part or the whole of this communication. Therefore a fair non-repudiation protocol has to generate non-repudiation of origin evidences intended to Bob, and non-repudiation of receipt evidences destined to Alice. In this paper, we clearly define the properties a fair non-repudiation protocol must respect, and give a survey of the most important non-repudiation protocols without and with trusted third party (TTP). For the later ones we discuss the evolution of the TTP's involvement and, between others, describe the most recent protocol using a transparent TTP. We also discuss some ad-hoc problems related to the management of non-repudiation evidences.

title: Non-Repudiation in Electronic Commerce
abstract: Electronic Commerce and Security. Repudiation and Dispute Resolution. Non-Repudiation and Network Security. Non-Repudiation in Message Handling Systems. Non-Repudiation in Electronic Payment Systems. Book Outline. Fundamentals of Non-Repudiation - Goals of Non-Repudiation. Non-Repudiation Services. Non-Repudiation Evidence. Roles of Trusted Third Parties. Phases of Non-Repudiation. Non-Repudiation Policy. Requirements for Non-Repudiation. Securing Digital Signatures for Non-Repudiation - Security Requirements on Digital Signatures. Time Stamps in Digital Signatures. Securing TTP's Digital Signatures. Time-Stamping Approach.  One-Way Sequential Link Approach.   Achieving Fair Non-Repudiation - Factors against Fair Non-Repudiation. Approaches for Fair Non-Repudiation.  Using Light-Weighted On-Line TTP.  Using Off-Line TTP without Timely Termination.  Using Off-Line TTP with Timely Termination.  Using In-Line TTP for Timely Delivery.  Related Work on Fair Non-Repudiation - Protocols Using In-Line TTP. Protocols Using On-Line TTP. Protocols Using Off-Line TTP. Protocols with Probablistic Fairness.  ISO's Non-Repudiation Mechanisms - Overview of ISO/IEC 13888. Mechanisms Using Symmetric Techniques. Mechanisms Using Asymmetric Techniques. Time-Stamping Evidence.  Case Studies - Non-Repudiation in Electronic Payment. Undeniable Billing in Mobile Communication.  Towards Formal Verification of Non-Repudiation - The SVO Logic. Formalization of Non-Repudiation. Verification of a Non-Repudiation Protocol.

title: Observations on Non-repudiation
abstract: This paper discusses non-repudiation services regarding the transfer of a message and classifies the roles of trusted third parties involved in non-repudiation services. We examine the selective receipt problem and the generation of time evidence, analyse the current state of the ISO/IEC 13888 drafts on non-repudiation mechanisms, and present a fair non-repudiation protocol including time evidence to promote the development of these drafts.

title: An Overlay Subscription Network for Live Internet TV Broadcast
abstract: We propose a framework, called overlay subscription network (OSN), for live Internet TV broadcast, where a subscriber can choose to watch at any time. This framework allows the source server to incrementally build a topology graph that contains the network connections not only from the server to each subscriber, but also among the subscribers themselves. With such a topology graph in place, we consider efficient overlay multicast for scalable OSN services. We first show that idling nodes, which do not receive video data for their own playback, can actually be used for data forwarding to significantly reduce the cost of overlay multicast. In light of this observation, we then propose a novel overlay multicast technique that distinguishes itself from existing schemes with these three aspects. First, the proposed technique is centered on the topology graph and can take advantage of the actual network connections among the subscribing nodes. Second, the new scheme is able to find and incorporate appropriate idling nodes in multicast to reduce network traffic. Third, with our approach, a node can be used in multiple multicast trees for data forwarding to improve the overall system performance. We evaluate the performance of the proposed technique through simulation. Our extensive studies show that the proposed framework has the potential to enable the Internet, a vehicle up to date mainly for transferring text and image data, for large-scale and cost-effective TV broadcast

title: Scalable simulation of large-scale wireless networks with bounded inaccuracies
abstract: Discrete event network simulators have emerged as popular tools for verification and performance evaluation for various wireless networks. Nevertheless, the desire to model such networks at high fidelity implies high computational costs, prohibiting most researchers from simulating wireless networks with thousands of nodes. There have been attempts on performance optimizations for large-scale wireless network simulation, but they have not appropriately modeled accumulation of weak interference, thereby suffering inaccuracies which may be magnified by upper layer protocols. This paper presents analysis of the effects of common optimization techniques for large-scale wireless network simulation on the overall network performance and also proposes modifications and novel techniques that introduce only limited inaccuracies or no additional inaccuracy at all. The study quantifies the effects of those optimizations on the simulation results for given thresholds and network parameters, and also identifies thresholds tolerable to most network studies. The experimental results show that these optimizations can improve the runtime performance of an already efficient wireless network simulator substantially, by a factor of up to 55 for wireless networks with 3200 nodes without compromising accuracy of the simulation results.

title: An alternative time management mechanism for distributed simulations
abstract: Over the past few years, there has been a keen interest in the management of time in distributed simulation environments. Previous emphasis in time management (TM) services has been based on time stamp ordering, which is both computation and bandwidth intensive. This article discusses an alternative approach to time management based on causal ordering. Traditional causal ordering protocols incur a large amount of communication overhead, which is generally of the order of N2 for a distributed system of N processes. A new causal ordering protocol proposed by the authors, the Modified Schiper-Eggli-Sandoz (MSES) protocol, is presented in this article. This new protocol minimizes the control information overhead of causal ordering by using the direct dependency tracking technique. The MSES protocol works well in both unicast and multicast environments, without relying on information about the underlying network topology and communication pattern among the processes of the distributed system. The MSES protocol has been successfully implemented as a middleware on top of DMSO RTI. Experiments have been conducted to benchmark the performance of the new time management mechanism with respect to the existing TM mechanisms available in DMSO RTI. The simulation scenarios of the experiments vary with different degrees of inter-federate dependency and federate event granularities. The ordering limitations of the causality based TM mechanism are addressed in this article and the trade-off of the degree of event ordering and execution speed of simulations is discussed.

title: Unconstrained numeral pair recognition using enhanced error correcting output coding: a holistic approach
abstract: This paper describes a new approach to recognize touching numeral strings. Currently most methods for numeral string recognition require segmenting the string image into separate numerals. As a result, the recognition system heavily depends on the reliability of the segmentation module. This study explores the holistic strategy directly on the string images without segmentation. It builds the novel classifier by combining binary classifiers based on data-driven error correcting output coding (DECOC). The dimensions of input images are reduced using principal components analysis. Support vector machines are used as base learners. Experiments on NIST SD19 touching numeral pairs confirm that DECOC can achieve favorable performance compared with other multi-class holistic classifiers. The method provides the flexibility of controlling the computational complexity versus accuracy. We also discuss an implementation suitable for distributing computing by decomposing the ensemble into subtasks.

title: Data driven approach to designing minimum hamming distance polychotomizer
abstract: A polychotomous classifier assigns an observation to one of the K categories with K > = 3. Multiple binary classifiers (K = 2) such as the popular Support Vector Machines can be combined to achieve multi-class classification. Commonly used approaches include the one-vs-others scheme and the one-vs-one (pairwise coupling) scheme. While literature reported better performance from pairwise coupling than one-vs-others, the number of base learners required by pairwise coupling is quadratic in K. Alternatively, error correcting output codes (ECOC) provides a more general framework for designing polychotomizers. It associates each class with a codeword, which provides the capability to unify the traditional schemes. However, the design of an effective "coding matrix" remains an open problem. We study one kind of ECOC polychotomizer that decodes using minimum hamming distance. We propose a novel data-driven way to design the codewords based on inter-cluster distance. It provides a systematic way to extend the traditional schemes and construct effective polychotomizers. Experiments are conducted on synthetic data and real world applications including UCI repository problems and CENPARMI handwritten numerals. Experiments show that the proposed scheme can achieve competitive accuracy compared with both traditional schemes, and the number of base learners is typically much less than the requirement of the pairwise scheme.