18687186
Trading Privacy for Trust
Both privacy and trust relate to knowledge about an entity. However, there is an inherent conflict between trust and privacy: the more knowledge a first entity knows about a second entity, the more accurate should be the trustworthiness assessment; the more knowledge is known about this second entity, the less privacy is left to this entity. This conflict needs to be addressed because both trust and privacy are essential elements for a smart working world. The solution should allow the benefit of adjunct trust when entities interact without too much privacy loss. We propose to achieve the right trade-off between trust and privacy by ensuring minimal trade of privacy for the required trust. We demonstrate how transactions made under different pseudonyms can be linked and careful disclosure of such links fulfils this right trade-off.
34386518
Privacy Recovery with Disposable Email Addresses
Disposable e-mail address (DEA) services are a privacy recovery mechanism for the growing spam problem. However, this problem is clearly more complex than simply closing DEA; as the rolling e-mail address protocols (REAP) system demonstrates, recovery approaches must accommodate different normal states.
7815359
Trust Transfer: Encouraging Self-recommendations Without Sybil Attack
Trading privacy for trust thanks to the linkage of pseudonyms has been proposed to mitigate the inherent conflict between trust and privacy. This necessitates fusionym, that is, the calculation of a unique trust value supposed to reflect the overall trustworthiness brought by the set of linked pseudonyms. In fact, some pieces of evidence may overlap and be overcounted, leading to an incorrect trust value. In this approach, self-recommendations are possible during the privacy/trust trade. However, this means that Sybil attacks, where thousands of virtual identities belonging to the same real-world entity recommend each other, are potentially easier to carry out, as self-recommendations are an integral part of the attack. In this paper, trust transfer is used to achieve safe fusionym and protect against Sybil attacks when pieces of evidence are limited to direct observations and recommendations based on the count of event outcomes. Trust transfer implies that recommendations move some of the trustworthiness of the recommending entity to the trustworthiness of the trustee. It is demonstrated and tailored to email anti-spam settings.
14098973
CryptoCache: a secure sharable file cache for roaming users
Small mobile computers are now sufficiently powerful to run many applications, but storage capacity remains limited so working files cannot be cached or stored locally. Even if files can be stored locally, the mobile device is not powerful enough to act as server in collaborations with other users. Conventional distributed file systems cache everything locally or not at all; there is no possibility to cache files on nearby nodes.In this paper we present the design of a secure cache system called CryptoCache that allows roaming users to cache files on untrusted file hosting servers. The system allows flexible sharing of cached files among unauthenticated users, i.e. unlike most distributed file systems CryptoCache does not require a global authentication framework.Files are encrypted when they are transferred over the network and while stored on untrusted servers. The system uses public key cryptography, which allows roaming users to selectively grant read and write access to others by entrusting them with respectively the public key or the private key.
16785661
Partial outsourcing: a new paradigm for access control
Various security models have been proposed in recent years for different purposes. Each of these aims to ease administration by introducing new types of security policies and models. This increases the complexity a system administrator is faced with. Ultimately, the resources expended in choosing amongst all of these models leads to less efficient administration.In this paper, we propose a new access control paradigm, which is already well established in virus and SPAM protection as partial delegation of administration to external expertise centres. Well-known vulnerabilities can be filtered out and known sources of attacks can be automatically blocked. We describe how partial outsourcing can be achieved in a secure way. A framework, which enables this process has already been developed.
7607582
Trust enhanced ubiquitous payment without too much privacy loss
Computational models of trust have been proposed for use in ubicomp environments for deciding whether to allow customers to pay with an e-purse or not. In order to build trust in a customer, a means to link transactions using the same e-purse is required. Roughly, trust is a result of knowledge. As the number of transactions increases, the resulting increase in knowledge about the user of the e-purse threatens privacy due to global profiling. We present a scheme (and its prototype) that mitigates this loss of privacy without forbidding the use of trust for smoothing payment by giving the opportunity to the user to divide trust (i.e. transactions) according to context (e.g. location, user's current activity or subset of shops).
7360842
Effective timestamping in databases
Abstract. Many existing database applications place various timestamps on their data, rendering temporal values such as dates and times prevalent in database tables. During the past two decades, several dozen temporal data models have appeared, all with timestamps being integral components. The models have used timestamps for encoding two specific temporal aspects of database facts, namely transaction time, when the facts are current in the database, and valid time, when the facts are true in the modeled reality. However, with few exceptions, the assignment of timestamp values has been considered only in the context of individual modification statements.This paper takes the next logical step: It considers the use of timestamping for capturing transaction and valid time in the context of transactions. The paper initially identifies and analyzes several problems with straightforward timestamping, then proceeds to propose a variety of techniques aimed at solving these problems. Timestamping the results of a transaction with the commit time of the transaction is a promising approach. The paper studies how this timestamping may be done using a spectrum of techniques. While many database facts are valid until now, the current time, this value is absent from the existing temporal types. Techniques that address this problem using different substitute values are presented. Using a stratum architecture, the performance of the different proposed techniques are studied. Although querying and modifying time-varying data is accompanied by a number of subtle problems, we present a comprehensive approach that provides application programmers with simple, consistent, and efficient support for modifying bitemporal databases in the context of user transactions.
1670342
Indexing of now-relative spatio-bitemporal data
Abstract. Real-world entities are inherently spatially and temporally referenced, and database applications increasingly exploit databases that record the past, present, and anticipated future locations of entities, e.g., the residences of customers obtained by the geo-coding of addresses. Indices that efficiently support queries on the spatio-temporal extents of such entities are needed. However, past indexing research has progressed in largely separate spatial and temporal streams. Adding time dimensions to spatial indices, as if time were a spatial dimension, neither supports nor exploits the special properties of time. On the other hand, temporal indices are generally not amenable to extension with spatial dimensions. This paper proposes the first efficient and versatile index for a general class of spatio-temporal data: the discretely changing spatial aspect of an object may be a point or may have an extent; both transaction time and valid time are supported, and a generalized notion of the current time, now, is accommodated for both temporal dimensions. The index is based on the R$^*$-tree and provides means of prioritizing space versus time, which enables it to adapt to spatially and temporally restrictive queries. Performance experiments are reported that evaluate pertinent aspects of the index.
14873521
Management of multiply represented geographic entities
Multiple representation of geographic information occurs when a real-world entity is represented more than once in the same or different databases. In this paper we propose a new approach to the modeling of multiply represented entities and the relationships among the entities and their representations. A multiple representation management system is outlined that can manage multiple representations consistently over a number of autonomous databases. Central to our approach is the multiple representation schema language that is used to configure the system. It provides an intuitive and declarative means of modeling multiple representations and specifying rules that are used to maintain consistency, match objects representing the same entity, and restore consistency if necessary.
16453065
Object-relational management of multiply represented geographic entities
Multiple representations occur when information about the same geographic entity is represented electronically more than once. This occurs frequently in practice, and it invariably results in the occurrence of inconsistencies among the different representations. We propose to resolve this situation by introducing a multiple representation management system (MRMS), the schema of which includes rules that specify how to identify representations of the same entity, rules that specify consistency requirements, and rules used to restore consistency when necessary. In this paper, we demonstrate by means of a prototype and a real-world case study that it is possible to implement a multiple representation schema language on top of an object-relational database management system. Specifically, it is demonstrated how it is possible to map the constructs of the language used for specifying the multiple representation schema to functionality available in Oracle. Though some limitations exist, Oracle has proven to be a suitable platform for implementing an MRMS.
1363543
Extending Existing Dependency Theory to Temporal Databases
Normal forms play a central role in the design of relational databases. Several normal forms for temporal relational databases have been proposed. These definitions are particular to specific temporal data models, which are numerous and incompatible. The paper attempts to rectify this situation. We define a consistent framework of temporal equivalents of the important conventional database design concepts: functional dependencies, primary keys, and third and Boyce-Codd normal forms. This framework is enabled by making a clear distinction between the logical concept of a temporal relation and its physical representation. As a result, the role played by temporal normal forms during temporal database design closely parallels that of normal forms during conventional database design. These new normal forms apply equally well to all temporal data models that have timeslice operators, including those employing tuple timestamping, backlogs, and attribute value timestamping. As a basis for our research, we conduct a thorough examination of existing proposals for temporal dependencies, keys, and normal forms. To demonstrate the generality of our approach, we outline how normal forms and dependency theory can also be applied to spatial and spatiotemporal databases.