Security Remarks on a Group Signature Scheme with Member Deletion
A group signature scheme allows a group member of a given group to sign messages on behalf of the group in an anonymous and unlinkable fashion. In case of a dispute, however, a designated group manager can reveal the signer of a valid group signature. Based on the Camenisch-Michels group signature scheme [7,8], Kim, Lim and Lee proposed the first group signature scheme with a member deletion procedure at ICISC 2000 . Their scheme is very efficient in both communication and computation aspects. Unfortunately, their scheme is insecure. In this paper, we first identify an effective way that allows any verifier to determine whether two valid group signatures are signed by the same group member. Secondly, we find that in their scheme a deleted group member can still update his signing key and then generate valid group signatures after he was deleted from the group. In other words, the Kim-Lim-Lee group signature scheme  is linkable and does not support secure group member deletion.

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: 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: 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: 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 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: A feedback-based approach for segmenting handwritten legal amounts on bank cheques
abstract: The proposed feedback-based approach is implemented in two steps. In the first step, segmentation is done according to the structural features between the connected components in the legal amounts. In the second step, a feedback process is introduced to re-segment the parts that could not be identified in the first step. Then a multiple neural network classifier is used to verify the re-segmentation result. The confidence value produced by the classifier is used to determine the best segmentation points. This approach is tested on a CENPARMI database and the result indicates that the correct segmentation rate increased by 13.4% from the previous approach.

title: TWINE: A Hybrid Emulation Testbed for Wireless Networks and Applications
abstract: In this paper, we present TWINE, a high fidelity, efficient emulation framework that combines the accuracy and realism of emulated and physical networks and the scalability and repeatability of simulation in an integrated testbed, for evaluation of real protocols and applications. Our measurements show that the TWINE emulation kernel has a memory footprint of less than 100KB, and occupies no more than 3.5% CPU cycles. Thanks to such small overhead and the accurate modelling of physical layer events(at microseconds level), application throughput measured in TWINE is within 5% of the measured throughput from an equivalent physical wireless LAN. A single commodity PC in TWINE can emulate at least four wireless hosts or simulate sixty nodes in real time at microseconds granularity. This paper also illustrates TWINE’s novel capabilities via two case studies: a protocol to maintain fairness in mesh networks and an adaptive streaming media application operating in heterogeneous wireless networks. The results from the case studies clearly show the benefit of the TWINE evaluation methodology, by identifying a mismatch between the performance of the protocol or application based on actual user experience versus its performance as measured using traditional network performance metrics such as application throughput.

title: Architecture Sensitive Database Design: Examples from the Columbia Group
abstract: In this article, we discuss how different aspects of modern CPU architecture can be effectively used by database systems. While we shall try to cover most important aspects of modern architectures, we shall not aim to provide an exhaustive survey of the literature. Rather, we will use examples from our own recent work to illustrate the principles involved. While there is related work on using other components of modern machines such as graphics cards and intelligent disk controllers for database work, we limit our discussion here to just a single CPU and the memory hierarchy (excluding disks). In recent years the primary focus of database performance research has fundamentally shifted from disks to main memory. Systems with a very large main memory allow a database’s working set to fit in RAM. At the same time processors have continued to double in performance roughly every eighteen months in line with “Moore’s Law,” while memory speed improvements have been marginal. The CPU now spends many hundreds of cycles waiting for data to arrive from main memory, and database workloads are often memory-bound. Because of this bottleneck, database research at Columbia and elsewhere has focused on effectively using the cache hierarchy to improve database performance. Changes in processor technology have also influenced database research. Modern processors feature a very long pipeline, which helps to provide better performance. It also results in a higher branch misprediction penalty, because the pipeline must be flushed and restarted when a branch is mispredicted. Modern CPUs provide the database programmer with a rich instruction set. Using specialized instructions, such as SIMD instructions, database performance can be improved by allowing a degree of parallelism and eliminating some conditional branch instructions, thus reducing the impact of branch mispredictions.

title: Understanding Human-Computer Interactions in Map Revision
abstract: It is difficult to track, parse and model human-computer interactions during editing and revising of documents, but it is necessary if we are to develop automated technologies that will aid or replace humans. This paper introduces a system for accessing and recording a stream of events related to human actions in a real-time cartographic map revision system. The recorded events are parsed into a sequence of meaningful user actions and an action representation in XML format is generated. We also report results of experiments on predicting user actions such as view changes, edits, road tracking/production using hidden Markov models.

title: An improved ellipse propagation model for location estimation in facilitating ubiquitous computing
abstract: Positioning is a crucial technology for ubiquitous computing. A directional propagation model - the ellipse propagation model (EPM) is proposed by our research group for locating a mobile station (MS) within a radio cellular network with an accuracy that can enable a number of location based services to realize ubiquitous computing. By using a geometric algorithm, the location of the mobile station can be estimated. However, since one parameter in our geometric algorithm is fixed, errors may be induced as the surrounding environment changes. In view of this, we would like to propose a new algorithm - the iterative algorithm to provide the positioning based on EPM. With the technical support of two local mobile phone operators, we have conducted a series of experiments using real data and experiment results showed that the proposed iterative algorithm outperforms the geometric algorithm by a good margin of 18% in terms of average error.