Abstract. Attack trees have found their way to practice because they have proved to be an intuitive aid in threat analysis. Despite, or perhaps thanks to, their apparent simplicity, they have not yet been provided with an unambiguous semantics. We argue that such a formal interpretation is indispensable to precisely understand how attack trees can be manipulated during construction and analysis. We provide a denotational semantics, based on a mapping to attack suites, which abstracts from the internal structure of an attack tree, we study transformations between attack trees, and we study the attribution and projection of an attack tree.

Attack-defense trees are a novel methodology for graphical security modeling and assessment. They extend the well known formalism of attack trees by allowing nodes that represent defensive measures to appear at any level of the tree. This enlarges the modeling capabilities of attack trees and makes the new formalism suitable for representing interactions between an attacker and a defender. Our formalization supports different semantical approaches for which we provide usage scenarios. We also formalize how to quantitatively analyze attack and defense scenarios using attributes.

Abstract. We introduce and give formal definitions of attack-defense trees. We argue that these trees are a simple, yet powerful tool to analyze complex security and privacy problems. Our formalization is generic in the sense that it supports different semantical approaches. We present several semantics for attack-defense trees along with usage scenarios, and we show how to evaluate attributes.

Abstract. We provide the first formal foundation of SAND attack trees which are a popular extension of the well-known attack trees. The SAND attack tree formalism increases the expressivity of attack trees by introducing the sequential conjunctive operator SAND. This operator enables the modeling of ordered events. We give a semantics to SAND attack trees by interpreting them as sets of series-parallel graphs and propose a complete axiomatization of this semantics. We define normal forms for SAND attack trees and a term rewriting system which allows identification of semantically equivalent trees. Finally, we formalize how to quantitatively analyze SAND attack trees using attributes.

In this paper we study the automation of test derivation and execution in the area of conformance testing. The test scenarios are derived from multiple specification languages: LOTOS, PROMELA and SDL. A central theme of this study is the usability of batch-oriented and on-the-fly testing approaches. To facilitate the derivation from multiple formal description techniques and the different test execution approaches, an open, generic environment called ToRX is introduced. ToRX enables plugging in existing or dedicated tools. We have carried out several experiments in testing a conference protocol, resulting in requirements on automated testing and benchmarking criteria.

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Multi-party contract signing protocols specify how a number of signers can cooperate in achieving a fully signed contract, even in the presence of dishonest signers. This problem has been studied in different settings, yielding solutions of varying complexity. Here we assume presence of a trusted third party that will be contacted only in case of a conflict, asynchronous communication, and a totally ordered protocol. Our goal is to develop a lower bound on the number of messages in such a protocol. Using the notion of abort chaining, which is a specific type of attack on the fairness of signing protocols, we derive the lower bound α 2 + 1, with α > 2 being the number of involved signers. In order to achieve this lower bound, we relate the problem of developing fair signing protocols to the open combinatorial problem of finding shortest permutation sequences. This relation also indicates a way to construct signing protocols which are shorter than current state-ofthe-art protocols. We illustrate this by presenting the shortest three-party fair contract signing protocol.

Abstract. The use of formal methods to verify security protocols with respect to secrecy and authentication has become standard practice. In contrast, the formalization of other security goals, such as privacy, has received less attention. Due to the increasing importance of privacy in the current society, formal methods will also become indispensable in this area. Therefore, we propose a formal definition of the notion of anonymity in presence of an observing intruder. We validate this definition by analyzing a well-known anonymity preserving protocol, viz. onion routing.