This paper presents a type-based information flow analysis for a call-by-value λ-calculus equipped with references, exceptions and let-polymorphism, which we refer to as Core ML. The type system is constraint-based and has decidable type inference. Its noninterference proof is reasonably light-weight, thanks to the use of a number of orthogonal techniques. First, a syntactic segregation between values and expressions allows a lighter formulation of the type system. Second, noninterference is reduced to subject reduction for a nonstandard language extension. Lastly, a semi-syntactic approach to type soundness allows dealing with constraint-based polymorphism separately.

We study a security property for processes in dynamic contexts, i.e., contexts that can be reconfigured at runtime. The security property that we propose in this paper, named Persistent BNDC, is such that a process is "secure" when every state reachable from it satisfies a basic Non-Interference property. We define a suitable bisimulation based equivalence relation among processes, that allows us to express the new property as a single equivalence check, thus avoiding the universal quantifications over all the reachable states (required by Persistent BNDC) and over all the possible hostile environments (implicit in the basic Non-Interference property we adopt). We show that the novel security property is compositional and we discuss how it can be efficiently checked.

In the analysis of security protocols, methods and tools for reasoning about protocol behaviors have been quite effective. We aim to expand the scope of those methods and tools. We focus on proving equivalences P ≈ Q in which P and Q are two processes that differ only in the choice of some terms. These equivalences arise often in applications. We show how to treat them as predicates on the behaviors of a process that represents P and Q at the same time. We develop our techniques in the context of the applied pi calculus and implement them in the tool ProVerif.

Distributed systems and applications are often expected to enforce high-level authorization policies. To this end, the code for these systems relies on lowerlevel security mechanisms such as, for instance, digital signatures, local ACLs, and encrypted communications. In principle, authorization specifications can be separated from code and carefully audited. Logic programs, in particular, can express policies in a simple, abstract manner. We consider

Noninterference is a property of sequential programs that is useful for expressing security policies for data confidentiality and integrity. However, extending noninterference to concurrent programs has proved problematic. In this paper we present a relatively expressive secure concurrent language. This language, based on existing concurrent calculi, provides first-class channels, higher-order functions, and an unbounded number of threads. Well-typed programs obey a generalization of noninterference that ensures immunity to internal timing attacks and to attacks that exploit information about the thread scheduler. Elimination of these refinement attacks is possible because the enforced security property extends noninterference with observational determinism. Although the security property is strong, it also avoids some of the restrictiveness imposed on previous securitytyped concurrent languages.

Abstract. Discretionary Access Control (DAC) systems provide powerful mechanisms for resource management based on the selective distribution of capabilities to selected classes of principals. We study a type-based theory of DAC models for concurrent and distributed systems represented as terms of Cardelli, Ghelli and Gordon’s pi calculus with groups [3]. In our theory, groups play the rôle of principals, and the structure of types allows fine-grained mechanisms to be specified to govern the transmission of names, to bound the (iterated) re-transmission of capabilities, to predicate their use on the inability to pass them to third parties,... and more. The type system relies on subtyping to help achieve a selective distribution of capabilities, based on the groups in control of the communication channels. Type preservation provides the basis for a safety theorem stating that in well-typed processes all names flow according to the delivery policies specified by their types, and are received at the intended sites with the intended capabilities. 1

Many programs operate reactively, patiently waiting for user input, subsequently running for a while producing output, and eventually returning to a state where they are ready to accept another input (or perhaps diverging). When a reactive program communicates with multiple parties, we would like to be sure that it can be given secret information from one without leaking it to others. In this paper, we explore various definitions of noninterference for reactive programs and identify two of special interest—one corresponding to terminationinsensitive noninterference for a standard sequential language, the other to termination-sensitive noninterference. We focus on the former and develop a proof technique for showing that program behaviors are secure according to this definition. To demonstrate the viability of the approach, we define a simple reactive language with an information-flow type system and apply our proof technique to show that well-typed programs are secure. 1

Abstract. We develop a theory of noninterference for a typed version of the π-calculus where types are used to assign secrecy levels to channels. We provide two equivalent characterizations of noninterference based on a typed behavioural equivalence relative to a security level σ, which captures the idea of external observers of level σ. The first characterization involves a universal quantification over all the possible active attacks, i.e., malicious processes which interact with the system possibly leaking secret information. The second definition of noninterference is expressed in terms of an unwinding condition, which deals with so-called passive attacks trying to infer confidential information just by observing the behaviour of the system. This unwinding-based characterization naturally leads to efficient methods for the verification and construction of (compositional) secure systems. Furthermore, we characterize noninterference in terms of bisimulation-like (partial) equivalence relations in the style of a stream of similar studies for other process calculi (e.g., CCS and CryptoSPA) and languages (e.g., imperative and multi-threaded languages). 1

Distributed systems and applications are often expected to enforce high-level authorization policies. To this end, the code for these systems relies on lower-level security mechanisms such as, for instance, digital signatures, local ACLs, and encrypted communications. In principle, authorization specifications can be separated from code and carefully audited. Logic programs, in particular, can express policies in a simple, abstract manner. We consider the problem of checking whether a distributed implementation based on communication channels and cryptography complies with a logical authorization policy. We formalize authorization policies and their connection to code by embedding logical predicates and claims within a process calculus. We formulate policy compliance operationally by composing a process model of the distributed system with an arbitrary opponent process. Moreover, we propose a dependent type system for verifying policy compliance of implementation code. Using Datalog as an authorization logic, we show how to type several examples using policies and present a general schema for compiling policies.

Discretionary Access Control (DAC) systems provide powerful resource management mechanisms based on the selective distribution of capabilities to selected classes of principals. We study a type-based theory of DAC models for a process calculus that extends Cardelli, Ghelli and Gordon’s pi-calculus with groups (Cardelli et al., 2005). In our theory, groups play the rôle of principals, the unit of abstraction for our access control policies, and types allow the specification of fine-grained access control policies to govern the transmission of names, to bound the (iterated) re-transmission of capabilities, to predicate their use on the inability to pass them to third parties. The type system relies on subtyping to achieve a selective distribution of capabilities, based on the groups that control the communication channels. We show that the typing and subtyping relationships of the calculus are decidable. We also prove a type safety result, showing that in well-typed processes (i) all names flow according to the access control policy specified by their types, and (ii) are received at the intended sites with the intended capabilities. We illustrate the expressive power and the flexibility of the typing system on several examples.