Mazurak, Karl
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Publication Evidence-Based Audit, Technical Appendix(2008-04-27) Vaughan, Jeffrey A; Jia, Limin; Mazurak, Karl; Zdancewic, Stephan AAuthorization logics provide a principled and flexible approach to specifying access control policies. One of their compelling benefits is that a proof in the logic is evidence that an access-control decision has been made in accordance with policy. Using such proofs for auditing reduces the trusted computing base and enables the ability to detect flaws in complex authorization policies. Moreover, the proof structure is itself useful, because proof normalization can yield information about the relevance of policy statements. Untrusted, but well-typed, applications that access resources through an appropriate interface must obey the access control policy and create proofs useful for audit. This paper presents AURA0, an authorization logic based on a dependently-typed variant of DCC and proves the metatheoretic properties of subject-reduction and normalization. It shows the utility of proof-based auditing in a number of examples and discusses several pragmatic issues that must be addressed in this context.Publication Linear Types, Protocols, and Processes in Classical F°(2013-01-01) Mazurak, KarlSession types and typestate both promise a type system that can reason about protocol adherence. The complexity budgets of most programming languages, however, do not allow for new forms of types aimed at specific problem domains--even domains as broad as these. Classical F◦ --read "F-pop"--is a typed λ-calculus based on classical (i.e., full) linear logic, wherein session types arise naturally from the interaction between the usual sums, products, and implications of linear logic and a simple process model, with the dualizing negation of classical logic naturally accounting for how a protocol is seen by each of a channel's endpoints. Classical F◦ expressions evaluate to processes, reminiscent of those in the π-calculus, that communicate over channels, but source expressions, rather than including processes and channels, employ only two novel control operators that account for process creation and communication. F◦ is introduced by way of its intuitionistic fragment, which even on its own can account for typestate: the combination of linearity and polymorphism leads to natural encodings of many programmer-specified protocols. In fact, any protocol expressible as a regular language can be encoded in an intuitionistic F◦ type. F◦ distinguishes between linear and unrestricted types by using kinds together with a notion of subkinding, avoiding the pitfalls of approaches based on type qualifiers or modalities; kinds are related by a subkinding order that allows unrestricted types to be treated as though they were linear. Soundness for intuitionistic and classical F◦ is proved both in the standard operational sense of preservation and progress and for an augmented semantics that shows more directly that the expected properties of linearity are preserved. This establishes the absence of deadlocks in closed, well-typed F◦ programs; it also guarantees that such programs will not "leak" processes as long as their result types are unrestricted.