PERVASIVE computing 53Trust is situation-specific; trust in one environment doesn't directly transfer to another environment. So a notion of context is necessary.Authorized licensed use limited to: TRINITY COLLEGE DUBLIN. Downloaded on January 21, 2009 at 05:54 from IEEE Xplore. Restrictions apply.them in a particular way-for example, to update old address book entries with accurate information. However, the principal could deviate from this expected behavior, and the combined likelihood and severity of this is the risk of granting them a privilege. Risk analysisIn SECURE, the risks of a trust-mediated action are decomposed by possible outcomes. Each outcome's risk depends on the other principal's trustworthiness (the likelihood) and the outcome's intrinsic cost. For example, an address update might itself be out-of-date or maliciously misleading. These two outcomes' costs would reflect the user's wasted time, and the likelihoods would depend on trust in the other party.An outcome's costs could span a range of values. For example, a user might have received a correct phone book entry. This third outcome's cost could show a net benefit to the user, as the user might successfully use it later. However, if the number became out-ofdate by the time it was used, that would be a net loss. To reflect this uncertainty, you might represent the distribution of costs as a cost-PDF (probability density function). Figure 1 illustrates a user contemplating a parameterized interaction with principal p. For each possible outcome, the user has a parameterized cost-PDF (a family of cost-PDFs) that represents the range of possible costs and benefits the user might incur should each outcome occur.While the risk evaluator assesses the possible cost-PDFs, the trust calculator provides information t that determines the risk's likelihood based on the principal's identity p and other parameters of the action. The risk evaluator then uses this trust information to select the appropriate cost-PDF.Finally, the request analyzer combines all the outcomes' cost-PDFs to decide if the action should be taken or to arrange further interaction. Because any uncertainty is preserved right up to the decision point, this allows more complex decision making than simple thresholding, allowing responses such as "not sure" if there isn't enough information.In our continuing example, if Liz's PDA received a phone number from Vinny's PDA, she might not think it was maliciously misleading based on her trust in Vinny's honesty. She might think it could be out-of-date, however, if Vinny had given her stale information before, attributing a higher risk to this outcome. Finally, she'd consider the potential benefit of having a correct number, again moderated by Vinny's trustworthiness. Liz's PDA would do all these calculations on her behalf using its model of her trust beliefs, as Figure 2 illustrates. If the benefits outweighed the other outcomes' costs, the PDA would then accept the information.On the other hand, if John-a colleague from a competing research gr...

Abstract. 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.

BackgroundIn addition to providing the molecular machinery for transcription and translation, recombinant microbial expression hosts maintain the critical genotype-phenotype link that is essential for high throughput screening and recovery of proteins encoded by plasmid libraries. It is known that Escherichia coli cells can be simultaneously transformed with multiple unique plasmids and thusly complicate recombinant library screening experiments. As a result of their potential to yield misleading results, bacterial multiple vector transformants have been thoroughly characterized in previous model studies. In contrast to bacterial systems, there is little quantitative information available regarding multiple vector transformants in yeast. Saccharomyces cerevisiae is the most widely used eukaryotic platform for cell surface display, combinatorial protein engineering, and other recombinant library screens. In order to characterize the extent and nature of multiple vector transformants in this important host, plasmid-born gene libraries constructed by yeast homologous recombination were analyzed by DNA sequencing.ResultsIt was found that up to 90% of clones in yeast homologous recombination libraries may be multiple vector transformants, that on average these clones bear four or more unique mutant genes, and that these multiple vector cells persist as a significant proportion of library populations for greater than 24 hours during liquid outgrowth. Both vector concentration and vector to insert ratio influenced the library proportion of multiple vector transformants, but their population frequency was independent of transformation efficiency. Interestingly, the average number of plasmids born by multiple vector transformants did not vary with their library population proportion.ConclusionThese results highlight the potential for multiple vector transformants to dominate yeast libraries constructed by homologous recombination. The previously unrecognized prevalence and persistence of multiply transformed yeast cells have important implications for yeast library screens. The quantitative information described herein should increase awareness of this issue, and the rapid sequencing approach developed for these studies should be widely useful for identifying multiple vector transformants and avoiding complications associated with cells that have acquired more than one unique plasmid.

Abstract. Trust is an essential component for secure collaboration in uncertain environments. Trust management can be used to reason about future interactions between entities. In reputation-based trust management, an entity's reputation is usually built on ratings from those who have had direct interactions with the entity. In this paper, we propose a Bayesian network based trust management model. In order to infer trust in different aspects of an entity's behavior, we use multidimensional application specific trust values and each dimension is evaluated using a single Bayesian network. This makes it easy both to extend the model to involve more dimensions of trust and to combine Bayesian networks to form an opinion about the overall trustworthiness of an entity. Each entity can evaluate his peers according to his own criteria. The dynamic characteristics of criteria and of peer behavior can be captured by updating Bayesian networks. Risk is explicitly combined with trust to help users making decisions. In this paper, we show that our system can make accurate trust inferences and is robust against unfair raters.

Abstract. Pervasive computing requires some level of trust to be established between entities. In this paper we argue for an entity recognition based approach to building this trust which differs from starting from more traditional authentication methods. We also argue for the concept of a "pluggable" recognition module which allows different recognition schemes to be used in different circumstances. Finally, we propose that the trust in the underlying infrastructure has to be taken into account when considering end-to-end trust.