Despite the globally recognized advantages of e-invoicing and various efforts to implement such systems, retailers and stores may still have difficulties in promoting purely paperless e-invoices due to the lack of a convenient and secure way for consumers to receive and retrieve the e-invoices. As such, paper-based invoices may still be issued along with e-invoices, contradicting an important benefit of e-invoicing — paper consumption reduction. Thanks to the advances in smart phones and Near Field Communication (NFC) technologies, e-invoices can be delivered via NFC-enabled smartpones, allowing consumers to examine the content immediately after transactions and to easily retrieve them later on. Still, an extra security mechanism is needed to ensure the integrity and non-repudiation of the content, as invoices may bear some value and thus become the target of a security attack. In this paper, we propose a secure NFC-based e-invoice remitting scheme using standard NFC P2P communications, and discuss how it fulfills major security requirements, including authenticity, integrity, and non-repudiation. The proposed system is also implemented and tested in Taiwan's e-invoicing system.

Software applications are increasingly relying on networks to function, but making programs to interact over the network is still tedious and error-prone. Conventional technologies such as CORBA and the WS-* stack are complicated to use, whereas Restful style operations rely on costly ad-hoc developments on a per-service basis. We believe the problem lies in the lack of a network protocol that can solely and sufficiently address interoperability needs. In light of this, we developed Internet Metaobject Protocol (IMOP), a remote method invocation protocol for object-based resource representations. IMOP thoroughly defines operations required to facilitate interactions, from reflecting a resource's definition to invoking its methods. It also rigorously defines the types of data passed between systems, including primitive types, composite value types, and reference types. All of these are programming language neutral.

BitTorrent's built-in mechanism can effectively encourage peers to upload while they are downloading, but it lacks a mechanism to incentivize peers to continually upload to benefit others after they have completed downloading. As such, many private BitTorrent sites have enforced a {sharing ratio} on their members to demand the minimum amount a peer must upload with respect to the amount it has downloaded. In this paper we study how sharing ratio enforcement affects download time by addressing the following problem: {Given a flash crowd of peers downloading a file, what is the time required for the last peer to finish downloading?} We propose two models to estimate the download time. The first model is simpler in the sense that it does not need to know peers' actual download rates during the downloading process. However, it needs to assume that every peer can fully utilize its uplink capacity. This assumption may not hold when there are much more peers to upload than to download, a scenario that is not uncommon in a system with sharing ratio enforcement. The second model lifts the assumption by extending an existing model for estimating peers' actual download rates in a system with no sharing ratio enforcement. However, estimating peers' actual download rates becomes very complex when the number of peers of different bandwidths increases.

Expert Seeking is a social network application that requires certain search strategies in the form of expert candidate-selection process. Assuming that no one in the network has the global knowledge, a query for expertise must be forwarded to, and between, candidates in order to reach the right person. During this candidate-selection process, a person determines whom to forward the query based only on the local information s/he knows. Two types of local information, actor profiles and structural attributes, may be used in devising search strategies. In this paper we conduct a comprehensive comparative study on search strategies using these types of information, as well as on search strategies using both types simultaneously to see if there is a synergy between them.

We present a structured P2P system called Donuts, which exploits proximity, achieves load balance, and supports range query. The motivation is that range query incurs many overlay contiguous traverses, so making overlay neighbors physically nearby can significantly reduce communication costs. However, building a proximity-aware network may compromise load balance, as efficient load balance requires flexibility of node placement so that a lightly loaded node can leave its position to join beside a heavily loaded node to share its load. To resolve the conflict, we introduce a new concept - grouping. The idea is to cluster physically nearby nodes into several overlay sections to increase the flexibility of proximity join, routing, and load balancing while maintaining key ranges in neighboring nodes adjacent. Moreover, grouping can improve search efficiency by taking advantage of cache. It can also increase fault tolerance, especially to local catastrophes. In the following we introduce Donuts by starting from a simple model and gradually moving into a refined and sophisticated one.

Although search by keywords is particularly important for resource and service discovery in P2P networks, existing techniques for keyword search in structured P2P overlays suffer from several problems: unbalanced load, hot spots, fault tolerance, storage redundancy, and unable to facilitate ranking and keyword expansion. In this paper, we present a general keyword index and search scheme for structured P2P networks that avoids these problems, and in which object insert, delete, and search can be efficiently performed. Some experimental results are also presented to support our claim.

We address wildcard search in structured peer-to-peer (P2P) networks, which, to our knowledge, has not yet been explored in the literature. We begin by presenting an approach based on some well-known techniques in information retrieval (IR) and discuss why it is not appropriate in a distributed environment. We then present a simple and novel technique to index objects for wildcard search in a fully decentralized manner, along with some search strategies to retrieve objects. Our index scheme, as opposed to a traditional IR approach, can achieve quite balanced loads, avoid hop spots and single point of failure, reduce storage and maintenance costs, and offer some ranking mechanisms for matching objects. We use the compact disc (CD) records collected in FreeDB (http://freedb.org) as the experimental data set to evaluate our scheme. The results confirm that our index scheme is very effective in balancing the load. Moreover, search efficiency depends on the information given in a query: the more the information, the higher the performance.

We present a simple yet novel technique for prefix search in P2P networks. The idea is to extract characters and their position information in a keyword to index objects. Our index scheme can achieve quite balanced loads, avoid hop-spots and single point of failure, reduce storage and maintenance costs, and offer some ranking mechanisms for matching objects. We use 2,412,613 CD records collected in FreeDB (http://freedb.org) as experimental dataset to test our index scheme.

Empirical studies have shown that participating nodes in peer-to-peer (P2P) systems are not equivalent. Some nodes, known as 'super peers', are more powerful and stable than the others. Such heterogeneity has been taken account into the design of P2P systems in two ways: by employing super peers to serve as index servers for query, and by routing through super peers to speed up query. In this paper, we use super peers to reduce maintenance cost in Chord.

Web applications often require users to provide personal information for customization, identification, or completing a transaction. However, the way we disclose our information in current cyberspace does not allow us to control the usage, release and circulation of the information, violating the basic principle of personal information privacy. Online personal data licensing (OPDL) is a framework to bring the control of personal information back to individuals by requiring application and service providers to obtain a license from a person before collecting, processing, and using his personal information. In this paper we present the license design and automation of the license negotiation process.

Existing techniques for keyword/attribute search in structured P2P overlays suffer from several problems: unbalanced load, hot spots, fault tolerance, storage redundancy, and unable to facilitate ranking. In this paper, we present a general keyword index and search scheme for structured P2P networks that avoids these problems, and in which object insert, delete, and search can be efficiently performed. Some experimental results are also presented to support our claim.

We propose a simple, practical, yet powerful index scheme to enhance search in unstructured P2P networks. The index scheme uses a data structure "Bloom Filters" to index files shared at each node, and then let nodes gossip to one another to exchange their Bloom filters. In effect, each node indexes a random set of files in the network, thereby allowing every query to have a constant probability to be successfully resolved within a fixed search space. The experimental results show that our approach can improve the search in Gnutella by an order of magnitude.

Conventional hierarchical organizations are inadequate in managing multi-dimensional artifacts such as publications. Much research has attempted at a more usable high dimensional information visualization and browsing experience, but has failed at the curse of dimensionality, exhibiting one or more of the following symptoms: (1) interface is unfamiliar, non-intuitive or cluttered; (2) dimensions viewable are limited or require to be in numeric domain; (3) update and/or browsing requires exponential time. This work proposes a hypercube artifact space model and an interactive browsing methodology, multi-dimension browse, which offers: (1) a familiar, intuitive and simple interface with summarization results; (2) browse against any and all dimensions; (3) update and browse costs linear in number of dimensions and artifacts respectively, and browse costs can be further reduced logarithmically on parallel platforms.

We propose a quorum system, which we referred to as the surficial quorum system, for group mutual exclusion. The surficial quorum system is geometrically evident and is easy to construct. It also has a nice structure based on which a truly distributed algorithm for group mutual exclusion can be obtained and processed loads can be minimized. When used with Maekawa's algorithm, the surficial quorum system allows up to /spl radic/2n/m(m-l) processes to access a resource simultaneously, where n is the total number of processes and m is the total number of groups. We also present two modifications of Maekawa's algorithm so that the number of processes that can access a resource at a time is not limited to the structure of the underlying quorum system, but to the number that the problem definition allows.

Mutual exclusion and concurrency are two fundamental and essentially opposite features in distributed systems. However, in some applications such as computer supported cooperative works (CSCW) we have found it necessary to impose mutual exclusion on different groups of processes in accessing a resource, while allowing processes of the same group to share the resource. To our knowledge, no such design issue has been raised in the literature. Our contributions are to present a new problem, which we refer to as the Congenial Talking Philosophers, to model the design issue for concurrency while mutual exclusion. We also propose several criteria to evaluate solutions of the problem and to measure their performance. Finally, we provide an efficient and highly concurrent distributed algorithm for the problem in a shared-memory model where processes communicate ...

We present MULTI, a symmetric, distributed, randomized algorithm that, with probability one, schedules multiparty interactions in a strongly fair manner. To our knowledge, MULTI is the first algorithm for strong interaction fairness to appear in the literature. Moreover, the expected time taken by MULTI to establish an interaction is a constant not depending on the total number of processes in the system. In this sense, MULTI guarantees real-time response. MULTI makes no assumptions (other than boundedness) about the time it takes processes to communicate. It, thus, offers an appealing tonic to the impossibility results of Tsay and Bagrodia, and Joung concerning strong interaction fairness in an environment, shared-memory, or message-passing, in which processes are deterministic and the communication time is nonnegligible. Because strong interaction fairness is as strong a fairness condition that one might actually want to impose in practice, our results indicate that randomization may also prove fruitful for other notions of fairness lacking deterministic realizations and requiring real-time response.

We present Multi, a symmetric, fully distributed, randomized algorithm that, with probability 1, schedules multiparty interactions in a strongly fair manner. To our knowledge, Multi is the first algorithm for strong interaction fairness to appear in the literature. Moreover, the expected time taken by Multi to establish an interaction is a constant not depending on the total number of processes in the system. In this sense, Multi guarantees real-time response. Multi makes no assumptions (other than boundedness) about the time it takes processes to communicate. It thus offers an appealing tonic to the impossibility results of Tsay&Bagrodia and Joung concerning strong interaction fairness in an environment, shared-memory or message-passing, in which processes are deterministic and the communication time is nonnegligible. Because strong interaction fairness is as strong a fairness condition that one might actually want to impose in practice, our results indicate that randomization may also prove fruitful for other notions of fairness lacking deterministic realizations and requiring real-time response.

The notion of completion has been proposed by Francez et al. to transform a non-equivalence-robust fairness notion to an equivalence-robust one while maintaining several properties of the source. However, a completion may not preserve strong-feasibility---a necessary and sufficient condition for a completion to be implementable. In this paper, we study the system requirement for a completion to be strongly-feasible, and determine the strongest implementable completion for every given fairness notion. Moreover, for most systems we obtain a fairness notion, which we refer to as SG + , such that SG + is the strongest fairness notion that is both implementable and equivalence-robust. Finally, we show that, if equivalence-robustness is dropped, then in general it is impossible to define a fairness notion that is implementable and stronger than all other implementable fairness notions. This implies plenty of leeway in the design of fairness notions suitable for various applications. 1 I...

A multipaq interaction is a set of I/0 actions executed jointly by a number of processes, each of which must be ready to execute its own action for any of the actions in the set to occur, An attempt to participate in an interaction delays a process until all other participants are available.Although a relatively new concept, the multiparty interaction has found its way into a number of distributed programming languages and algebraic models of concurrency.In this paper, we present a taxonomy of languages for multiparty interaction that covers all proposals of which we are aware.Based on this taxonomy, we then present a comprehensive analysis of the computational complexity of the multipa~interaction scheddirrg prob[em, the problem of scheduling multiparty interactions in a given execution environment.

A first-order multiparty interaction is an abstraction mechanism that defines communication among a set of formal process roles . Actual processes participate in a first-order interaction by enroling into roles, and execution of the interaction can proceed when all roles are filled by distinct processes. As in CSP, enrolement statements can serve as guards in alternative commands. The enrolement guard-scheduling problem then is to enable the execution of first-order interactions through the judicious scheduling of roles to processes that are currently ready to execute enrolement guards. We present a fully distributed and message-efficient algorithm for the enrolement guard-scheduling problem, the first such solution of which we are aware. We also describe several extensions of the algorithm, including: generic roles; dynamically changing environments , where processes can be created and destroyed at run time; and nested-enrolement , which allows interactions to be nested.

We present a taxonomy of languages for multiparty interaction, which covers all proposals of which we are aware. Based on this taxonomy, we present a comprehensive analysis of the computational complexity of the multiparty interaction implementation problem, the problem of scheduling multiparty interactions in a given execution environment.

A first-order multiparty interaction is an abstraction mechanism that defines communication among a set of formal process roles. Actual processes participate in a first-order interaction by enroling into roles, and execution of the interaction can proceed when all roles are filled by distinct processes. As in CSP, enrolement statements can serve as guards in alternative commands. The enrolement guard scheduling problem then is to enable the execution of first-order interactions through the judicious scheduling of roles to processes currently ready to execute enrolement guards. We present a fully distributed and message-efficient algorithm for the enrolement guard scheduling problem, the first such solution of which we are aware. We also describe several extensions of the algorithm, including generic roles, dynamically changing environments where processes can be created and destroyed at run time, and nested-enrolement which allows interactions to be nested.