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.
14146996
Cryptographic access control in a distributed file system
Traditional access control mechanisms rely on a reference monitor to mediate access to protected resources. Reference monitors are inherently centralized and existing attempts to distribute the functionality of the reference monitor suffer from problems of scalability.Cryptographic access control is a new distributed access control paradigm designed for a global federation of information systems. It defines an implicit access control mechanism, which relies exclusively on cryptography to provide confidentiality and integrity of data managed by the system. It is particularly designed to operate in untrusted environments where the lack of global knowledge and control are defining characteristics.The proposed mechanism has been implemented in a distributed file system, which is presented in this paper along with a preliminary evaluation of the proposed mechanism.
16254824
Trust Propagation in Small Worlds
The possibility of a massive, networked infrastructure of diverse entities partaking in collaborative applications with each other increases more and more with the proliferation of mobile devices and the development of ad hoc networking technologies. In this context, traditional security measures do not scale well. We aim to develop trust-based security mechanisms using small world concepts to optimise formation and propagation of trust amongst entities in these vast networks. In this regard, we surmise that in a very large mobile ad hoc network, trust, risk, and recommendations can be propagated through relatively short paths connecting entities. Our work describes the design of trust-formation and risk-assessment systems, as well as that of an entity recognition scheme, within the context of the small world network topology.
2275333
Risk probability estimating based on clustering
Ubiquitous computing environments are highly dynamic, with new unforeseen circumstances and constantly changing environments, which introduces new risks that cannot be assessed through traditional means of risk analysis. Mobile entities in a ubiquitous computing environment require the ability to perform an autonomous assessment of the risk incurred by a specific interaction with another entity in a given context. This assessment will allow a mobile entity to decide whether sufficient evidence exists to mitigate the risk and allow the interaction to proceed. Such evidence might include records of prior experiences, recommendations from a trusted entity or the reputation of the other entity. We propose a dynamic mechanism for estimating the risk probability of a certain interaction in a given environment using hybrid neural networks. We argue that traditional risk assessment models from the insurance industry do not directly apply to ubiquitous computing environments. Instead, we propose a dynamic mechanism for risk assessment, which is based on pattern matching, classification and prediction procedures. This mechanism uses an estimator of risk probability, which is based on the automatic clustering of defining features of the environment and the other entity, which helps avoid subjective judgments as much as possible.
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.
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.
1879036
On the Semantics of "Now" in Databases
While "now" is expressed in SQL as CURRENT-TIMESTAMP within queries, this value cannot bestored in the database. However, this notion of an ever-increasing current-time value has beenreflected in some temporal data models by inclusion of database-resident variables, such as"now," "until-changed," "âˆž," "@" and "-." Time variables are very desirable, but their usealso leads to a new type of database, consisting of tuples with variables, termed a variabledatabase.This paper proposes a framework for defining the semantics of the variable databases of temporalrelational data models. A framework is presented because several reasonable meaningsmay be given to databases that use some of the specific temporal variables that have appearedin the literature. Using the framework, the paper defines a useful semantics for such databases.Because situations occur where the existing time variables are inadequate, two new types ofmodeling entities that address these shortcomings, timestamps which we call now-relative andnow-relative indeterminate, are introduced and defined within the framework. Moreover, the paperprovides a foundation, using algebraic bind operators, for the querying of variable databasesvia existing query languages. This transition to variable databases presented here requires minimalchange to the query processor. Finally, to underline the practical feasibility of variabledatabases, we show that database variables can be precisely specified and efficiently implementedin conventional query languages, such as SQL, and in temporal query languages, suchas TSQL2.
1273427
Semantics of Time-Varying Information
Abstract This paper provides a systematic and comprehensive study of the underlying semantics of temporal databases, summarizing the results of an intensive collaboration between the two authors over the last five years. We first examine how facts may be associated with time, most prominently with one or more dimensions of valid time and transaction time. One common case is that of a bitemporal relation , in which facts are associated with timestamps from exactly one valid-time and one transaction-time dimension. These two times may be related in various ways, yielding temporal specialization . Multiple transaction times arise when a fact is stored in one database, then later replicated or transferred to another database. By retaining the transaction times, termed temporal generalization , the original relation can be effectively queried by referencing only the final relation. We attempt to capture the essence of time-varying information via a very simple data model, the bitemporal conceptual data model . Emphasis is placed on the notion of snapshot equivalence of the information content of relations of different data models. The logical design of temporal databases is a natural next topic. Normal forms play a central role during the design of conventional relational databases. We show how to extend the existing relational dependency theory, including the dependencies themselves, keys, normal forms, and schema decomposition algorithms, to apply to temporal relations. However, this theory does not fully take into account the temporal semantics of the attributes of temporal relations. To address this deficiency, we study the semantics of individual attributes. One aspect is the observation and update patterns of attributes—when an attribute changes value and when the changes are recorded in the database, respectively. A related aspect is when an attribute has some value, termed its lifespan . Yet another aspect is the values themselves of attributes—how to derive a value for an attribute at any point in time from stored values, termed temporal derivation . This study of attribute semantics leads to the formulation of temporal guidelines for logical database design.
14443105
The COST Benchmark-Comparison and Evaluation of Spatio-temporal Indexes
An infrastructure is emerging that enables the positioning of populations of on-line, mobile service users. In step with this, research in the management of moving objects has attracted substantial attention. In particular, quite a few proposals now exist for the indexing of moving objects, and more are underway. As a result, there is an increasing need for an independent benchmark for spatio-temporal indexes. 
 
This paper characterizes the spatio-temporal indexing problem and proposes a benchmark for the performance evaluation and comparison of spatio-temporal indexes. Notably, the benchmark takes into account that the available positions of the moving objects are inaccurate, an aspect largely ignored in previous indexing research. The concepts of data and query enlargement are introduced for addressing inaccuracy. As proof of concepts of the benchmark, the paper covers the application of the benchmark to three spatio-temporal indexes—the TPR-, TPR*-, and Bx-trees. Representative experimental results and consequent guidelines for the usage of these indexes are reported.
8086987
Multidimensional data modeling for complex data
Online Analytical Processing (OLAP) systems considerably ease the process of analyzing business data and have become widely used in industry. Such systems primarily employ multidimensional data models to structure their data. However current multidimensional data models fall short in their abilities to model the complex data found in some real world application domains. The paper presents nine requirements to multidimensional data models, each of which is exemplified by a real world, clinical case study. A survey of the existing models reveals that the requirements not currently met include support for many-to-many relationships between facts and dimensions, built-in support for handling chance and time, and support for uncertainty as well as different levels of granularity in the data. The paper defines an extended multidimensional data model, and an associated algebra, which address all nine requirements.
34647773
Conceptual Data Modeling for Spatiotemporal Applications
Many exciting potential application areas for database technology manage time-varying, spatial information. In contrast, existing database techniques, languages, and associated tools provide little built-in support for the management of such information. The focus of this paper is on enhancing existing conceptual data models with new constructs, improving their ability to conveniently model spatiotemporal aspects of information. The goal is to speed up the data modeling process and to make diagrams easier to comprehend and maintain. Based on explicitly formulated ontological foundations, the paper presents a small set of new, generic modeling constructs that may be introduced into different conceptual data models. The ER model is used as the concrete context for presenting the constructs. The semantics of the resulting spatiotemporal ER model, STER, is given in terms of the underlying ER model. STER is accompanied by a textual counterpart, and a CASE tool based on STER is currently being implemented, using the textual counterpart as its internal representation.