# Ettekanded

#### Venanzio Capretta: The Construction of Infinity

Ettekande kiled. [pdf]

Abstract: The status of infinity has been a philosophical battleground since Antiquity. Greek philosophers already debated whether it can be conceived as existing in actuality or just as potential unboundedness. The treatment of actual infinite objects has been seen across history as a province of metaphysics or as a technical trick to solve some mathematical problems. Starting with Cantor, infinite sets of different sizes have been given a precise mathematical status, leading eventually to modern set theory. However, fierce criticism was fired at this conception by constructivist and predicativist thinkers.

In recent decades, significant advances have been made in the constructive understanding of infinity. At first it may seem that computer science should be impervious to any notion of infinite object: computers are discrete machines with a finite memory. Surprisingly, mathematical methods to represent infinite objects and compute with them have been devised. It even turns out that some computational problems are best solved by using infinite data structures.

I will give a brief historical review of the computational treatment of infinity and explain the basic mathematical notions that are being developed in this field.

#### Marlon Dumas: Model Transformations for Business Process Analysis and Execution

Ettekande kiled. [ppt]

Abstract: A business process model is a representation of the way an organization operates to achieve a goal, such as delivering a product or a service. For example, a business process model may describe the activities (both manual and automated) performed within an insurance company to handle an insurance claim lodged by a customer. Business process models serve multiple purposes. On the one hand, business and system analysts use process models to identify and evaluate business improvement options or to define system requirements. On the other hand, software developers are concerned with the automated execution of business processes based on detailed models. Depending on the purpose, a business process may be modeled at different abstraction levels and using different languages. This talk will review various challenges raised by the definition of model transformations aimed at bridging between different business process modeling languages. The talk will discuss transformations from popular business process modeling notations to variants of Petri nets and state machines to support automated analysis, as well as two-way transformations from high-level to executable process modeling languages.

#### Phaedra Agius: Typing Staphylococcus aureus using the Protein A gene

Ettekande kiled. [ppt]

Abstract: With the emergence of drug resistant strains, Staphylococcus aureus represents a significant human health threat. Identifying the family types efficiently and quickly is crucial in community settings. Here, we develop a novel hybrid sequence algorithm approach to type this bacterium using only its spa gene, a method that is cheaper than the Multi locus sequence typing (MLST) method which uses 7 housekeeping genes. Our resulting spa groups correlate strongly with those defined by MLST. Furthermore, our methods can be fine-tuned to be more discriminative so that new strains can be identified. Finally, we performed data projection to visualize the data and the relationships between isolates. The proposed methodology provides a promising new approach to molecular epidemiology.

#### Dan Bogdanov: Optimizing execution time in a distributed virtual processor

Ettekande kiled. [pdf]

Abstract: We are developing a method for privacy-preserving data processing. Our solution comes in the form of a distributed virtual processor that can execute privacy-preserving operations. The data is stored in a secret-shared form and we have designed a suite of multi-party computation protocols for performing computations on such data. We have proven that these protocols preserve privacy also when composed with each other, so we can write programs for the processor and expect them not toleak data.

My talk will be about Sharemind - our software implementation of this processor. We are constantly measuring the performance of operations on Sharemind and exploring methods for making the system faster. I will give an overview of the benchmarks we've done and discuss the conclusions we've made.

You can find out more about Sharemind at http://sharemind.cs.ut.ee/.

#### Juhan Ernits: Principles of Symmetry Reductions in Verification and Testing

Ettekande kiled. [pdf]

Abstract: In model checking and model-based testing it is often necessary to perform an equivalent of the whole state space traversal of a model. Two general reduction techniques - partial order reduction and symmetry reduction enable to reduce the space that needs to be traversed in order to conclude whether certain property holds or not. We will give an overview of the state of the art in symmetry reduction. We will look at how scalar sets work and how they are related to orbit problem in group theory. Then we will proceed to how static topologies can help reducing the state space. Finally we will look at state isomorphism based symmetry reduction and how such symmetry reduction can be performed in several stages to reduce the overall computational complexity. The examples are provided using tools like Uppaal, NModel and Groove.

#### Jevgeni Kabanov: Generic Memoizing Recursion

Ettekande kiled. [pdf]

Abstract: In this talk we introduce a new combinator, inspired by comonadic recursion schemes developed by Uustalu, Vene and Pardo. This combinator not only generalizes the existing recursion schemes, but also provides some interesting insights in the nature of optimal memoizing computation.

#### Peeter Laud: Program transformations for cryptographic proofs

Ettekande kiled. [pdf]

Abstract: Traditionally, the core of a cryptographic reduction (proof that a primitive A is secure on the premise that some primitive B is secure) has been the construction of a program of the adversary successfully attacking A, assuming access to a routine that successfully attacks B. The proof of correctness of this program (that it indeed breaks A; and presents the correct view to the subroutine breaking B) is an integral part of the reduction. The size of the adversary is often substantial and its sturcture is complex. Hence it may be nigh impossible to verify its correctness by hand. The tool support for such a verification is also lacking --- it is hard to formalize arguments about (conditional) probabilities and events that happen negligibly often.

For quite some time, the security definitions of cryptographic primitives have been formalized by stating that two experiments cannot be distinguished by any adversary. These experiments are specified as (small) programs; the definition thus states that two programs are indistinguishable in certain contexts. If we write down the construction of the primitive A (from the primitive B) as a program, too, then we can search for a subprogram in its code, also appearing in the security definition of B, and replace it with the other program from B's security definition. The transformed primitive can then be transformed again, until we reach a program that is obviously secure. The proof is thus decomposed into several steps that can all be verified independently. The steps can be made small enough, such that their verification does not pose many problems. In this way we can increase our confidence in the correctness of the proof. Tool support for automatic verification or generation would be feasible, too.

In the tutorial I will demonstrate this technique in the security proofs of cryptographic primitives, as well as in the static analysis of programs and protocols for certain security properties.

#### Riina Maigre: Web services composition software with visual user interface

Ettekande kiled. [pdf]

Abstract: We propose a service composition method based on higher order workflows. Method allows automatic generation of higher order workflows with precise semantics for automatic web service composition. Implementation of proposed composition method is developed in visual languages development framework CoCoViLa. The implemented tool allows to describe service composition workflows and service models in a simple visual language. It allows us to reason about the reachability of goals on the described workflow or generate workflows from service models. In addition BPEL or OWL-S composite service descriptions can be generated.

#### Oleg Mürk: Deductive Verification of C Programs with KeY

Ettekande kiled. [pdf]

Abstract: In this talk I will present a Dynamic Logic for deductive verification of type-safe C programs (CDL). It allows verification of C programs w.r.t. operation contracts and invariants. Our approach is based on the KeY Dynamic Logic (DL) and tool, previously targeted on Java. We have extended the KeY architecture to support language variability - DLs for new programming languages can be implemented as a plugin to the KeY tool. Based on this we have created KeY-C - a tool for deductive verification of C programs.

You can find out more about the KeY project at http://www.key-project.org/.

#### Ulrich Norbisrath: Friend-To-Friend (F2F) Computing

Ettekande kiled. [pdf]

Abstract: Nowadays, grids are very heavyweight and complex, especially submitting small jobs is in no relation to the administrative support needed to run the grid infrastructure. The initial metaphor for the computational grid being as easy as a power grid is still unfulfilled. The resources in Grids are centrally managed by IT professionals. Hence, they create a considerable amount of work to administer and maintain.

To facilitate a public usage of Grids, we extend Grid computing with techniques from peer-to-peer computing combined with instant messaging. Instant messaging is used by the vast majority of computer users. We assume, that using instant messaging techniques for the administrative part of setting up the Grid will open Grid capabilities to the public and enable thereby a personal Desktop Grid. It provides a new approach for authentication and authorization.

Analogue to peer-to-peer the here applied paradigm is called friend-to-friend computing (F2F computing) as a contraction of Grid, peer-to-peer, and friends relating to the spontaneously formed social networks. Like skype made voice-over-ip usable by everyone, F2F computing could facilitate the usage of distributed computational power.

#### Andres Ojamaa: Simulation in Cyber Security

Ettekande kiled. [pdf]

Abstract: This talk gives an overview of simulation in cyber security. What kinds of problems there exist and what can be done using computer simulations to improve the situation. The talk introduces a few software packages for modeling and simulation of computer networks. Finally, some new and planned features of CoCoViLa to support simulation in cyber security are described.

#### Hellis Tamm: Transition minimality of bideterministic automata

Ettekande kiled. [pdf]

Abstract: Bideterministic automata are deterministic finite automata with the property of their reversal automata also being deterministic. It can be easily seen that any bideterministic automaton is a minimal DFA. Bideterministic automata have previously been shown to be unique (up to an isomorphism) minimal NFAs with respect to the number of states. In this talk, we discuss transition minimality issues of these automata. Bideterministic automata are transition-minimal NFAs. However, as this transition minimality is not necessarily unique, we also present the necessary and sufficient conditions for a bideterministic automaton to be uniquely transition-minimal among NFAs. Furthermore, bideterministic automata are transition-minimal $\epsilon$-NFAs.

#### Enn Tõugu: Computing and Computer Science in the Soviet Baltic Region

Ettekande kiled. [pdf]

Abstract: This talk includes references at events, people and trends in computing in the three Baltic states: Latvia, Lithuania and Estonia during their Soviet period. The Soviet computing science and practice could be divided into league A and league B. The first was for defense industry and power structures, the second for wide public. Although the Baltic computing belonged in essence to the league B, its scientific results were on the level with the league A. The historic perspective taken demonstrates also the changes in computer sciemce content in general.

#### Tarmo Uustalu: Intuitionistic propositional logic and proof search: What you could consider knowing

Ettekande kiled. [pdf]

Abstract: I'll discuss an easily formulated problem: find a proof of a given formula in intuitionistic propositional logic or an inhabitant of a given type in simply-typed lambda calculus. I'll touch upon the issues in backward search of sequent-style proofs (solved either by loop-detection or a switch to a contraction-free sequent calculus) and go then on to the cool little-known idea that I explain as forward search of natural deduction proofs (but that also goes under the names of the inverse method, Mints-style resolution and Stålmarck's method). Time permitting, I'll show Augustsson's Djinn program.

#### Jan Willemson: A multiplication protocol for $2n+1$ parties secure against $n$ semi-honest adversaries

Abstract: In 2007, Dan Bogdanov and Sven Laur proposed a framework for secure computations that achieves information-theoretic security against one semi-honest adversary. However, their protocols are heavily optimized for just three parties. In this talk we show, how to generalize one of the protocols (secure multiplication) to $2n+1$ parties achieving security against $n$ semi-honest adversaries.

#### Juhan Ernits et al.: Interactive Seminar: Writing and Taking Referee Reports

Seminari kiled. [pdf]

Liina Kamm
Peeter Laud
Helger Lipmaa
Tarmo Uustalu
Varmo Vene
Viimane uuendus 29.01.2008