Independence and concurrent separation logic

A compositional Petri net-based semantics is given to a simple language allowing pointer manipulation and parallelism. The model is then applied to give a notion of validity to the judgements made by concurrent separation logic that emphasizes the process-environment duality inherent in such rely-guarantee reasoning. Soundness of the rules of concurrent separation logic with respect to this definition of validity is shown. The independence information retained by the Petri net model is then exploited to characterize the independence of parallel processes enforced by the logic. This is shown to permit a refinement operation capable of changing the granularity of atomic actions

Non Interference for Intuitionist Necessity

The necessity modality of intuitionist S4 is a comonad. In this paper, we study indexed necessity modalities that provide the logical foundation for a variety of applications; for example, to model possession of capabilities in policy languages for access control, and to track exceptions in type theories for exceptional computation. Noninterference properties of the intuitionist logic of indexed necessity modalities capture the limitations on the information flow between formulas that are under the scope of necessity modalities with different indices. The impact of noninterference is seen in the unprovability of certain formulas. Noninterference is necessary for several applications. In models of capabilities, noninterference facilitates distributed reasoning. In models of exceptions, noninterference is necessary to ensure that the exceptions are tracked conservatively. In this paper, we prove noninterference properties for indexed intuitionist necessity S4 modalities. To our knowledge, this is the first examination of noninterference results for the intuitionist S4 necessity modality (even without indexing)

Full Abstraction for PCF

An intensional model for the programming language PCF is described, in which the types of PCF are interpreted by games, and the terms by certain "history-free" strategies. This model is shown to capture definability in PCF. More precisely, every compact strategy in the model is definable in a certain simple extension of PCF. We then introduce an intrinsic preorder on strategies, and show that it satisfies some striking properties, such that the intrinsic preorder on function types coincides with the pointwise preorder. We then obtain an order-extensional fully abstract model of PCF by quotienting the intensional model by the intrinsic preorder. This is the first syntax-independent description of the fully abstract model for PCF. (Hyland and Ong have obtained very similar results by a somewhat different route, independently and at the same time). We then consider the effective version of our model, and prove a Universality Theorem: every element of the effective extensional model is definable in PCF. Equivalently, every recursive strategy is definable up to observational equivalence.Comment: 50 page

Lambda-RBAC: Programming with Role-Based Access Control

We study mechanisms that permit program components to express role constraints on clients, focusing on programmatic security mechanisms, which permit access controls to be expressed, in situ, as part of the code realizing basic functionality. In this setting, two questions immediately arise: (1) The user of a component faces the issue of safety: is a particular role sufficient to use the component? (2) The component designer faces the dual issue of protection: is a particular role demanded in all execution paths of the component? We provide a formal calculus and static analysis to answer both questions.Comment: LMC

Evaluation of normal variants of circle of Willis at MRI

Background: Anatomy of circle of Willis (COW) shows extensive variations in different individuals and signifies the causation and presentation of clinical disease. The present study aims to evaluate the different anatomical variations of the Circle of Willis (COW) in general population, using magnetic resonance (MR) 3D-time of flight angiography and to correlate the observations with age and gender characteristics.Methods: This observational clinical study was conducted January 2013 to March 2014 in 503patients who were referred for MRI – Brain. MRI (Philips 1.5 Tesla magnet) with routine brain sequences along with 3D –TOF MRA was done in all patients. The anatomical variants of the anterior and posterior components of the COW were studied. The complete COW was assessed and the diameters of all the components were measured. The correlation between the vessel diameters in relations to age and gender were evaluated.Results: The mean age group of study participants was 42 years. Male dominance was seen among participants (57.1%). The complete configuration of the circle was seen in 31.6% of population. Most common anterior variant is type A (normal anterior configuration) with a prevalence of 52.9% and posterior variant is type K with a prevalence of 32.9%. Average diameters of the proximal vessels supplying the COW were larger in the older age subjects (centripetal vessels, the right and left ICA s and BA). Statistically significant differences between the mean vessel diameters between males and females were seen in the ICA-RT, ICA-LT, and PCOA-LT.Conclusions: The present study showed great variability of the anatomy of the COW in asymptomatic person. Various variants of COW can be picked up by MRA which is safer and non-invasive when compared with CTA / DSA. Knowledge of these variations would help in planning surgical procedures as well as preventing unwanted interventions

Succour to the Confused Deputy Types for Capabilities

Abstract. The possession of secrets is a recurrent theme in security literature and practice. We present a refinement type system, based on indexed intuitonist S4 necessity, for an object calculus with explicit locations (corresponding to principals) to control the principals that may possess a secret. Type safety ensures that if the execution of a well-typed program leads to a configuration with an object p located at principal a, then a possesses the capability to p. We illustrate the type system with simple examples drawn from web applications, including an illustration of how Cross-Site Request Forgery (CSRF) vulnerabilities may manifest themselves as absurd refinements on object declarations during type checking. This is an extended version of a paper that appears in APLAS 2012