Software is pervasive in our lives. We are accustomed to dealing with the failures of much of that software - restarting an application is a very familiar solution. Such solutions are unacceptable when the software controls our cars, airplanes and medical devices or manages our private information. These applications must run without error. SPARK provides a means, based on mathematical proof, to guarantee that a program has no errors. SPARK is a formally defined programming language and a set of verification tools specifically designed to support the development of software used in high integrity applications. Using SPARK, developers can formally verify properties of their code such as information flow, freedom from runtime errors, functional correctness, security properties and safety properties. Written by two SPARK experts, this is the first introduction to the just-released 2014 version. It will help students and developers alike master the basic concepts for building systems with SPARK.

Trust management systems are frameworks for authorization in modern distributed systems, allowing remotely accessible resources to be protected by providers. By allowing providers to specify policy, and access requesters to possess certain access rights, trust management automates the process of determining whether access should be allowed on the basis of policy, rights, and an authorization semantics. In this paper we survey modern state-of-the-art in trust management authorization, focusing on features of policy and rights languages that provide the necessary expressiveness for modern practice. We characterize systems in light of a generic structure that takes into account components of practical implementations. We emphasize systems that have a formal foundation, since security properties of them can be rigorously guaranteed. Underlying formalisms are reviewed to provide necessary background.

This letter reports the first observation of resonant tunneling negative differential resistance (NDR) through a double barrier GaAs-AlxGa1−xAs -GaAs-AlxGa1−x As-GaAs structure at room temperature. The NDR yields radio frequency oscillations at 300 K in a coaxial cable circuit that compare closely to those of a standard 1N3716 tunnel diode.

Distributed authorization takes into account several elements, including certificates that may be provided by non-local actors. While most trust management systems treat all assertions as equally valid up to certificate authentication, realistic considerations may associate risk with some of these elements, for example some actors may be less trusted than others. Furthermore, practical online authorization may require certain levels of risk to be tolerated. In this paper, we introduce a trust management logic based on the system RT that incorporates formal risk assessment. This formalization allows risk levels to be associated with authorization, and authorization risk thresholds to be precisely specified and enforced. We also develop an algorithm for automatic authorization in a distributed environment, that is directed by risk considerations. A variety of practical applications are discussed.

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