The article introduces a new formal system, the calculus of cooperation, for reasoning about coalitions of players in a certain class of games. The calculus is an extension of the propositional intuitionistic logic that adds a coalition parameter to intuitionistic implication. The system is shown to be sound and complete with respect to a game semantics. One intended application of the calculus of cooperation is the verification of privacy properties in multiparty computation protocols. The article argues that such properties can be established by providing a set of strategies for a non-zero-sum, perfect information game based on the protocol. It concludes with several examples of such verifications formalized in the calculus of cooperation.

The paper introduces and studies the ternary relation "secret a reveals at least as much information about secret c as secret b." In spite of its seeming simplicity, this relation has many non-trivial properties. The main result is a complete infinite axiomatization of the propositional theory of this relation.

The paper proposes Logic of Secrets in Collaboration Networks, a formal logical system for reasoning about a set of secrets established over a fixed configuration of communication channels. The system's key feature, a multi-channel relation called independence, is a generalization of a two-channel relation known in the literature as nondeducibility. The main result is the completeness of the proposed system with respect to a semantics of secrets.

For two years, we have been teaching a quarter-long compiler construction course where students implement an interpreter for a variant of the XML query language XQuery. Our goal is to motivate students' interest in the course by exposing them to an interesting and powerful new language which they see as relevant to potential future experiences. In this paper, we first explain the workings of the course itself, and then describe some pedagogically interesting variants of the XQuery language. We close with a discussion of challenges faced and conclusions.

We address the problem of establishing a group key amongst a dynamic group of users over an unreliable, or lossy, network. We term our key distribution mechanisms self-healing because users are capable of recovering lost group keys on their own, without requesting additional transmissions from the group manager thus cutting back on network traffic, decreasing the load on the group manager and reducing the risk of user exposure through traffic analysis. A user must be a member both before and after the session in which a particular key is sent in order to be able to recover the key through self-healing. Binding the ability to recover keys to membership status enables the group manager to use short broadcasts to establish group keys, independent of the group size. In addition, the self-healing approach to key distribution is stateless, meaning that a group member who has been off-line for some time is able to recover new session keys immediately after coming back on-line.

We consider the authentication of digital streams over a lossy network. The overall approach taken is graph-based, as this yields simple methods for controlling overhead, delay, and the ability to authenticate, while serving to unify many previously known hash- and MAC-based techniques. The loss pattern of the network is defined probabilistically, allowing both bursty and random packet loss to be modeled. Our authentication schemes are customizable by the sender of the stream; that is, within reasonable constraints on the input parameters, we provide schemes that achieve the desired authentication probability while meeting the input upper bound on the overhead per packet. In addition, we demonstrate that some of the shortcomings of previously known schemes correspond to easily identifiable properties of a graph, and hence, may be more easily avoided by taking a graph-based approach to designing authentication schemes.