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In pervasive computing environments, changes in context may trigger changes in an individual's access permissions. We contend that existing access control frameworks do not provide the fine-grained revocation needed to enforce these changing authorizations. In this paper, we present an authorization framework, in the context of the Gaia OS for active spaces, which integrates context with authorization and provides fine-grained control over the enforcement of dynamically changing permissions using cryptographic mechanisms. Our design, implemented in middleware, addresses the limitations of traditional authorization frameworks and the specific access control needs of pervasive computing environments. As part of our proposed framework, we define cryptographic protocols that enforce access to the system's communication channels and provide secure delivery of messages. We also provide a proof of correctness of key agreement and freshness using the standard BAN deduction system.

Multi-tier web server systems are used in many important contexts and their security is a major cause of concern. Such systems can exploit strategies like least privilege to make lower tiers more secure in the presence of compromised higher tiers. In this paper, we investigate an extension of this technique in which higher tiers are required to provide evidence of the authentication of principals when they make requests of lower tiers. This concept, which we call redundant authentication, enables lower tiers to provide security guarantees that improve significantly over current least privilege strategies. We validate this technique by applying it to a practical Building Automation System (BAS) application, where we explore the use of redundant authentication in conjunction with an authentication proxy to enable interoperation with existing enterprise authentication services.

Rapid increases in temperature during the “dormant period” of Ca3SiO5 paste hydration cause a high degree of solution supersaturation in respect to Ca(OH)2. This thermally induced instability creates an increased number of stable Ca(OH)2 nuclei, resulting in a significant increase in the number of Ca(OH)2 crystals and a decrease in the average Ca(OH)2 size in the hydrated paste. The treatment also results in an increased rate of hydration. Unlike low‐porosity ceramic systems where changes in precipitate size and distribution influence strength, the change in size and distribution of Ca(OH)2 crystals in C3S pastes had no apparent influence on strength when all strength was considered as a function of gel‐space ratio.