SRM seminar

Abstracts 2014

Speaker: Anton Wijs
Title: GPU-Based Graph Decomposition into Strongly Connected and Maximal End Components
Abstract: I will present parallel algorithms for component decomposition of graph structures on General Purpose Graphics Processing Units (GPUs). In particular, I will consider the problem of decomposing sparse graphs into strongly connected components, and decomposing stochastic games (such as Markov decision processes) into maximal end components. These problems are key ingredients of many standard and probabilistic graph algorithms, for instance in model checking, to verify properties of state spaces, or in the analysis of biological networks, with or without probabilistic interactions. (This is joint work with Joost-Pieter Katoen and Dragan Bosnacki.)

Speaker: Andrzej Mizera
Title: Probabilistic Boolean Networks: a modelling framework for large biological systems
Abstract: Computational modelling of biological machinery in a living cell (e.g., gene regulatory networks or signal transduction pathways) often leads to dynamical models characterised by huge state spaces of sizes that surpass the sizes of any human-designed systems by orders of magnitude. Therefore, profound understanding of biological processes asks for the development of new methods and tools that would provide means for formal analysis and reasoning about such huge systems. In this talk, we consider Probabilistic Boolean Networks (PBNs), a computational modelling framework that extends the famous concept of Boolean Networks, originally introduced by Stuart Kauffman in 1969 for the study of dynamical properties of gene regulatory networks. One of the key aspects in the analysis of PBNs is the comprehension of their steady-state (long-run) behaviour. For example, attractors of these discrete dynamical systems are of special interest as they were hypothesised to correspond to functional cellular states such as proliferation, apoptosis, or differentiation. We discuss the challenges that arise in the context of the study of the steady-state dynamics of large biological models and we present our solutions to this problem.

Speaker: Federica Paci
Title: How do you know that a security risk assessment method work? An empirical approach
Abstract:
Security risk assessment is a key tool to identify security threats and mitigations (a.k.a requirements) early in the system design life cycle and thus to avoid costly re-design of the system at later stages.

A security risk assessment can be performed following many of the different methodologies available on the market like OCTAVE, MAGERIT, BSI IT-Grundschutz, NIST 800-30, ISO 2700x or are proposed by academics like CORAS, Misuse Cases, and SI*. Each of them claim that they offer well-defined methods, techniques and guidelines for how to do conduct a risk assessment in practice. But what if these methods do not work in practice? Critical vulnerabilities may be overlooked and also lead to costly re-design of the system. A key research question is therefore “How do we evaluate if these methods are successful in identifying security risks?’’

In this talk I will report the results of the empirical studies, and in particular the experimental protocol that we designed to compare security risk assessment methods, its execution to compare academic and industrial methods for security risk assessment and some preliminary results on which are relevant features that affect the success of a security risk assessment method. I will conclude with some lessons learned that may be interesting for those who want to conduct this kind of research.

Speaker: Vincenzo Iovino
Title: Simulation-based secure functional encryption in the random oracle model
Abstract:
In recent years, there has been great interest in Functional Encryption (FE), a generalization of traditional encryption where a token enables a user to learn a specific function of the encrypted data and nothing else. One of the main lines of research in the area has consisted in studying the security notions for FE and their achievability. This study was initiated by [Boneh et al. -- TCC'11, O'Neill -- ePrint'10] where it was first shown that for FE the indistinguishability-based (IND) security notion is not sufficient in the sense that there are FE schemes that are provably IND-Secure but concretely insecure. For this reason, researchers investigated the achievability of Simulation-based (SIM) security, a stronger notion of security. Unfortunately, the above-mentioned works and others [e.g., Agrawal et al. -- CRYPTO'13] have shown strong impossibility results for SIM-Security. One way to overcome these impossibility results was first suggested in the work of Boneh et al. where it was shown how to construct, in the Random Oracle (RO) model, SIM-Secure FE for restricted functionalities and was asked the generalization to more complex functionalities as a challenging problem in the area. Subsequently, [De Caro et al. -- CRYPTO'13] proposed a candidate construction of SIM-Secure FE for all circuits in the RO model assuming the existence of an IND-Secure FE scheme for circuits with RO gates. This means that the functionality has to depend on the RO, thus it is not fixed in advance as in the standard definitions of FE. Moreover, to our knowledge there are no proposed candidate IND-Secure FE schemes for circuits with RO gates and they seem unlikely to exist. In this paper, we propose the first constructions of SIM-Secure FE schemes in the RO model that overcome the current impossibility results in different settings. We can do that because we resort to the two following models:

In the public-key setting we assume a bound q on the number of queries but this bound only affects the running-times of our encryption and decryption procedures. We stress that our FE schemes in this model are SIM-Secure and have ciphertexts and tokens of constant-size, whereas in the standard model, the current SIM-Secure FE schemes for general functionalities [De Caro et al., Gorbunov et al. -- CRYPTO'12] have ciphertexts and tokens of size growing as the number of queries.

In the symmetric-key setting we assume a timestamp on both ciphertexts and tokens. This is reasonable because, in the symmetric-key setting, there is only one user that encrypts and generates tokens. In this model, we provide FE schemes with short ciphertexts and tokens that are SIM-Secure against adversaries asking an unbounded number of queries.

Both results also assume the RO model, but not functionalities with RO gates and rely on extractability obfuscation w.r.t. distributional auxiliary input [Boyle et al. -- TCC'14] (and other standard primitives) secure only in the standard model.

Speaker: Mark Manulis
Title: Cryptographic Password Authentication with TLS Channel Bindings
Abstract: Cryptographic password-based authentication protocols on the Internet have failed to see wide-spread adoption on the Internet despite of a rich variety of PAKE protocols. In particular, due to the fact that most proposals require extensive modifications to the Transport Layer Security (TLS) protocol, which is challenging to realize. In this talk I will present two modular constructions where a cryptographically secure password-based mutual authentication protocol is run inside a confidential (but not necessarily authenticated) channel such as TLS and is bound to this channel to prevent man-in-the-middle and phishing attacks without requiring any modifications to the original channel protocol. For this purpose two channel binding mechanisms for TLS from RFC 5929 are utilized and their security is analyzed in the proposed general model for Password-Authenticated and Confidential Channel Establishment (PACCE), which can be seen as an extension of the ACCE model, which has been widely used for the security analysis of the TLS protocol. Moreover, our general results can be applied to integrate cryptographic password-based authentication into other channels beyond those established through the TLS protocol.

Speaker: Marcello Stanisci
Title: RX language: providing security through role-based labelling
Abstract:
Given a set of users in a system, roles are recursively defined as: subsets of users, or delegation between roles. The RX language, by using roles as security labels for sensible objects, aims to guarantee both security (preventing unwanted information flows) and flexibility (allowing roles' updating). Since roles' updatings could themselves reveal how system's security lattice is defined, RX provides constructs to label roles' updatings as well, called metapolicies labels. This way, we ensure that only allowed users have the right to observe security lattice's mutations. In this talk, we will see how RX is designed: from syntactic rules to semantics.

Speaker: Amir Herzberg
Title: AnonPoP: the Anonymous Post-Office Protocol
Abstract:
Anonymous Post-office Protocol (AnonPoP) is a messaging protocol ensuring strong anonymity to senders and recipients, even against powerful adversaries. AnonPoP is practical, scalable and efficient, with reasonable overhead in latency and communication. Furthermore, it is appropriate even for use in mobile devices, with modest, reasonable energy consumption (validated experimentally), and with good security even against MitM adversaries and even for disconnection-intersection attacks.

To provide anonymity and unobservability even against MitM attackers, AnonPoP uses Post-Office Servers, which keep anonymous mailboxes, and Mixes, between the Post-office and senders/recipients. The Post-Office is aware of the total amount of traffic in the system, but not of traffic patterns of individual senders and recipients. AnonPoP uses efficient cryptographic mechanisms, to ensure anonymity even against a malicious post office, who can also be MitM on all network traffic (and control some mixes).

AnonPop supports many diverse scenarios and applications, with an expressive mailbox authorization policy, including defenses against spam and Denial-of-Service.

Speaker: Jiuyong Li
Title: Two probabilistic models for privacy preserving data publishing
Abstract:
Data publishing is an easy and economical means for data sharing, but the privacy risk is a major concern in data publishing. Privacy preservation is a vital task in data sharing for organizations like hospitals. While a large number of data publishing models and methods have been proposed, their utility is of concern when a high privacy requirement is imposed. In this talk, I will present two probabilistic models for privacy preserving data publications.

In the first model we cap the belief of an adversary inferring a sensitive value in a published data set to as high as that of an inference based on public knowledge. The semantic meaning is that when an adversary sees a record in a published data set, s/he will have a lower confidence that the record belongs to a victim than not. The second model deals with inference of confidential information by using multiple published data sets, called composition attack. The model is designed to mitigate the risk of a composition attack by independent publication (without coordination). Both models have been implemented and assessed in comparison with some benchmark models. Their strengths and weaknesses will be discussed.

Speaker: Mark Ryan
Title: Balancing Societal Security and Individual Privacy: Accountable Escrow System
Abstract:
Individual privacy is a core human need, but society sometimes has the requirement to do targetted, proportionate investigations in order to provide security. To reconcile individual privacy and societal security, we explore whether we can have surveillance in a form that is verifiably accountable to citizens. This means that citizens get verifiable proofs of how much surveillance actually takes place.

Joint work with Jia Liu and Liqun Chen.

Speaker: Yang Zhang
Title: Location Prediction: Communities Speak Louder than Friends
Abstract: Humans are social animals and they interact with different communities of friends to conduct different activities. The literature shows that human mobility is constrained by their social relations as well as geographic constraints. In this paper, we investigate the social impact of a person's communities on his mobility, instead of all friends from his online social networks. This can be particularly useful, as not all online friends are really true friends and certain behaviors are influenced by specific communities but not all friends. To achieve our goal, we first develop a measure to characterize a person's social diversity, which we term `community entropy'. Through analysis of a real-life dataset, we demonstrate that a person's mobility is influenced only by a small fraction of his communities and the influence depends on the social contexts of the communities. We then exploit machine learning techniques to develop two models capturing features of communities and friends separately to predict the location of persons' future movement. Experimental results show that the model based on communities leads to more effective predictions.

Speaker: David Safranek
Title: Model Checking of Biological Systems
Abstract: The goal of computational systems biology is to develop models that can predict and explain unknown facts about the dynamics of biological systems, especially, non-trivial behaviour emerging from the interplay among the enormous number of individual biochemical components. The models are based on known first principles, wet-lab measurements, and existing hypotheses available in literature. A lot of information remains unknown, e.g., quantitative parameters such as rates of individual biochemical events. All the known or expected biological facts can be formalized in temporal logics. Model checking techniques known from formal verification can be then used to explore models with respect to a given set of temporal properties (dynamical constraints). The space of uncertainty in models can be then restricted by means of these constraints. This gives the modellers a powerful alternative to traditional parameter fitting methods. In this talk, an overview of applications of model checking to biological models will be given. In particular, we will focus on deterministic models—traditional differential (kinetic) models and their discrete abstractions. Two case studies of applying model checking to biological systems will be presented, in particular, gene regulation of mammalian cell cycle and ammonium transport in E. coli.

Speaker: Alina Vdovina
Title: Expander Graphs and Beyond
Abstract: We'll present various construction of expanders, old and new, and their application to hash functions.

Speaker: Sasa Radomirovic
Title: A Complete Characterization of Secure Human-Server Communication
Abstract: Establishing a secure channel from a human to a remote communication partner is a nontrivial problem. Humans cannot perform cryptographic computations without supporting technology, yet this technology may be compromised. Models and verification methods that consider humans as protocol actors tend to be either complex or restricted to specific protocols. We introduce a general communication topology model to facilitate the analysis of security protocols in this setting. We use this model to completely characterize all topologies that allow secure communication between a human and a remote server via a compromised personal computer.
These topologies are relevant for a variety of applications, including Internet voting and online banking. Our characterization can serve to guide the design of novel solutions and it allows one to quickly exclude proposals that cannot possibly offer secure communication.

Speaker: Taolue Chen
Title: Perturbation Analysis in Veriﬁcation of Discrete-Time Markov Chains
Abstract: Perturbation analysis in probabilistic verification addresses the robustness and sensitivity problem for verification of stochastic models against qualitative and quantitative properties. We identify two types of perturbation bounds, namely non-asymptotic bounds and asymptotic bounds. Non-asymptotic bounds are exact, pointwise bounds that quantify the upper and lower bounds of the verification result subject to a given perturbation of the model, whereas asymptotic bounds are closed-form bounds that approximate non-asymptotic bounds by assuming that the given perturbation is sufficiently small. We perform perturbation analysis in the setting of Discrete-time Markov Chains. We consider three basic matrix norms to capture the perturbation distance, and focus on the computational aspect. Our main contributions include algorithms and tight complexity bounds for calculating both non-asymptotic bounds and asymptotic bounds with respect to the three perturbation distances.

Speaker: Qiang Tang
Title: Search in Encrypted Data: Some Results and Open Problems
Abstract: The concept of searchable encryption has been proposed for over ten years. During this period, it has attracted a lot of attention and resulted in a large number of publications. In this talk, we will briefly review some (important) results in the literature, and show some open problems. We wish to raise some discussions among researchers from different research areas and identify some interesting research directions for the future.

Speaker: Jeroen van de Graaf
Title: On unconditional privacy and anonymity
Abstract: In light of Snowden's revelation there is a need to reassess the topic of unconditional (or everlasting) privacy and anonymity. In the first part of this talk we address the following problem: if a small group of people share a large file of random bits (> 1GB) to be used as one-time pad key material, how do they avoid collisions, i.e. two users using the same key material. In the second part we will discuss recent improvements on the Dining Cryptographer's protocol. In particular we will outline a scheme which offers verifiability, i.e. all participants show they are following faithfully. Our proposal offers unconditional privacy and is in this respect a dual of Golle-Juels (recently implemented as Verdict), in which privacy is based on computational assumptions. The practical significance of this research is that DC-based protocols could provide an alternative to TOR, the onion routing network protocol, whose uses mix nets as underlying cryptographic primitive.

Speaker: Leonid Volkov
Title: Two years of electronic elections for Russian opposition with eDemos
Abstract: eDemos is a software startup to provide "digital democracy as a service", which has been first implemented to serve as a platform for the elections to the coordination council of Russian opposition in October 2012. Having successfully withstood massive DDoS-attacks inspired by the government, the system provided over 170K voters with an opportunity to make the choice among 200+ candidates to the 45 seat council. Since that, eDemos became a de facto standard for civil initiatives and non-goverment elections in Russia. It has been also deployed for internet "alternative" elections of Iranian president in June 2013. Leonid Volkov, eDemos co-founder, will talk about the technology behind eDemos, but mostly about practical aspects of organizing a real wide scale electronic elections in a hostile environment.

Speaker: Sebastian Eggert
Title: Noninterference: Unwinding and Dynamics
Abstract: Noninterference is a notion for specifying and analyzing illegal information flows and causal dependencies in security related systems. We present a formal theory for state-based noninterference in a setting where different security policies-we call them dynamic policies-apply in different states of a given system. Our theory comprises appropriate security definitions, characterizations of these definitions, for instance in terms of unwindings, algorithms for analyzing the security of systems with dynamic policies, and corresponding complexity results.

Speaker: Mahmoud Mohsen
Title: Threat modeling: Theory vs. Practice
Abstract:
During the last couple of decades, different approaches of threat analysis and modeling have been introduced. In 1999, Schneier introduced the concept of attack trees which he defined as a formal, methodical way of describing the security of systems, based on varying attacks. Schneier argued that by using attack trees as a modeling technique, we would be able to understand all the different ways that can be exploited to attack our systems. Aren't we? According to his argument, we will be able then to design countermeasures to defend our systems. A few years later, the notation of attack graphs have been used and it wasn't clear whether it is the same as attack trees or not. Some considered attack graphs as a different way of threat modeling because it focuses more on the sequence of events rather than the event abstraction. However, attack graphs can be seen as a possible extension for attack trees and it can be modeled and formalized based on the attack trees formalization.

Different techniques have been developed to construct both attack trees and attack graphs. Security experts started to write them manually based on system's configuration, but later they realized that this may be very complex ending with trees and graphs containing thousands of nodes. At this point, lot of trials have been performed to automatically generate the attack graphs with the least possible input from the user to make it practical enough to be used in real dynamic large systems. However, the question of whether these threat modeling techniques are really useful in practice or they are just theoretical concepts is still raised. In this talk, we will discuss new models that have been developed to automatically generate attack graphs focusing on an approach that generate approximate attack graphs based on traffic data and network flows. We will also try to find the links between those theoretical approaches which are well modeled and formalized and the new practical techniques.

Speaker: Reza Shokri
Title: Computational Privacy: Two Fundamental Problems
Abstract: New services are being introduced and new businesses are flourishing by mining the rich flow of individuals' information over the Internet. This success, however, comes at a price of users' privacy. Businesses might misuse user data, and governments can massively track individuals. My research focuses on designing privacy-preserving schemes for emerging technologies. In my talk, I will present two fundamental challenges in computational privacy: quantification of users' privacy, and its protection using obfuscation mechanisms. I will present a metric and an analytical framework, based on statistical inference, to consistently quantify privacy across different systems. I will then introduce a new theoretical methodology to design privacy -protection obfuscation mechanisms that optimally balance privacy versus utility, and are provably robust against any attack. I will show examples of these approaches in the context of location-based services along with technical methods for quantifying and protecting location privacy.

Speaker: Ravi Jhawar
Title: Securing Operations in Vulnerable Networks
Abstract:
A large networked system is typically vulnerable to a wide range of cyber-attacks. The impact of such attacks on the applications deployed in the network ranges from simple response time degradation to complete unavailability and loss of critical data.

Existing solutions mainly improve security either by designing the network using defense tools such as intrusion detection systems and firewalls, or by developing applications using security measures such as data obfuscation and memory management. However, they fail to take into account the complex interdependencies between the network infrastructure, application tasks, and residual vulnerabilities in the system.

This talk discusses an approach to improve the security of applications, given the vulnerability state of the network. First, we consider the vulnerability distribution within the network and deploy applications while minimizing their exposure to residual vulnerabilities. Then, we apply network hardening techniques using attack graphs to protect the deployed applications from possible cyber-attacks.

Speaker: Christian Franck
Title: Dining Cryptographers with Verifiable Collision Resolution
Abstract: The dining cryptographers protocol is the most secure protocol for untraceable communication known in computer science. A problem of the protocol is that malicious participants can disrupt communication by deliberately creating collisions. We show that it is possible to verify that each participant correctly executes a collision resolution algorithm.

Speaker: Richard Clayton
Title: Privacy/Proxy/Perfidy - what criminals (and others) put in domain whois
Abstract:
Dr Richard Clayton has recently completed a major study of the `whois' contact details for domain names used in malicious or harmful Internet activities. ICANN wanted to know if a significant percentage of these domain registrations used privacy or proxy services to obscure the perpetrator's identity? No surprises in the results: Yes!

What was perhaps surprising was that quite a significant percentage of domains used for lawful and harmless activities ALSO used privacy and proxy services.

But the real distinction is that for maliciously registered domains, then contact details are hidden in a range of different ways so that 9 out 10 of these registrants are a priori uncontactable - whereas the a priori uncontactable rate varies between a quarter and at most two- thirds for the non-malicious registrations.

This talk discusses how these results were obtained and what their implications are for the future of the whois system. It also reports on spin-off research, inquiring into what happens to online banking domains when the bank is merged or is shut down - although remain owned by banks, a great many end up being used for somewhat dubious purposes.

Speaker: Sven Übelacker
Title: The Social Engineering Personality Framework
Abstract:
We explore ICT security in a socio-technical world and focus in particular on the susceptibility to social engineering attacks. We pursue the question if and how personality traits influence this susceptibility. This allows us to research human factors and their potential impact on the physical and digital security domains. We show how Cialdini's principles of influence can be used to explain why most social engineering attacks succeed and that these attacks mainly rely on peripheral route persuasion.

A comprehensive literature review reveals that individual values of a victim's personality traits relate to social engineering susceptibility. Furthermore, we construct suggestions for plausible relations between personality traits of the Five-Factor Model (Big 5) and the principles of influence. Based on these arguments, we propose our "Social Engineering Personality Framework" (SEPF). It supports and guides security researchers in developing holistic detection, mitigation, and prevention strategies while dealing with human factors.

Speaker: Olga Gadyatskaya
Title: FSquaDRA: Fast Detection of Repackaged Mobile Applications
Abstract: The ease of Android applications repackaging and proliferation of application clones in Google Play and other markets call for new effective techniques to detect repackaged code and combat distribution of cloned applications. Today all existing techniques for application repackaging detection are based on code similarity or feature (e.g., permission set) similarity evaluation. We propose a new approach to detect repackaging based on the resource files available in application packages. The intuition behind our approach is that malicious repackaged applications still need to maintain the "look and feel" of the originals by including the same images and other resource files, even though they might have additional code included or some of the original code removed. To evaluate the reliability of our approach we perform a comparison of the resource files-based similarity scores computed by our tool FSquaDRA with the code-based similarity scores of the popular AndroGuard tool for a dataset of randomly selected application pairs, and our results demonstrate strong positive correlation of the FSquaDRA resource-based score with the code-based similarity score.

Speaker: Michel Abdalla
Title: RKA Security for PRFs Beyond the Linear Barrier
Abstract: Related Key Attacks (RKAs) concern the security of cryptographic primitives in the situation where the key can be manipulated by the adversary. In the RKA setting, the adversary's power is expressed through the class of related-key deriving (RKD) functions which the adversary is restricted to using when modifying keys. Bellare and Kohno (Eurocrypt 2003) first formalised RKAs and pin-pointed the foundational problem of constructing RKA-secure Pseudo-Random Functions (RKA-PRFs). To date, the only constructions for RKA-PRFs under standard assumptions are due to Bellare and Cash (Crypto 2010) and it is a major open problem to construct RKA-PRFs for larger classes of RKD-functions. We make significant progress on this problem. We first show how to repair the Bellare-Cash framework for constructing RKA-PRFs and extend it to handle the more challenging case of classes of RKD-functions that contain claws. We apply this extension to show that a variant of the Naor-Reingold function already considered by Bellare and Cash is an RKA-PRF for a class of affine RKD-functions under the DDH assumption, albeit with an exponential-time security reduction. We then develop a second extension of the Bellare-Cash framework, and use it to show that the same Naor-Reingold variant is actually an RKA-PRF for a class of degree d polynomial RKD-functions Φ_d under the stronger Decisional d-Diffie-Hellman Inversion assumption. As a significant technical contribution, our proof of this result avoids the exponential-time security reduction that was inherent in the work of Bellare and Cash and in our first result.

Speaker: Cas Cremers
Title: Actor Key Compromise: Consequences and Countermeasures
Abstract:
Despite Alice's best efforts, her long-term secret keys may be revealed to an adversary. Possible reasons include weakly generated keys, compromised key storage, subpoena, and coercion. However, Alice may still be able afterwards to communicate securely with other parties. Whether this is possible depends on the protocol used. We call the associated property resilience against Actor Key Compromise (AKC). We formalise this property in a symbolic model and identify conditions under which it can and cannot be achieved. In case studies that include TLS and SSH, we find that many protocols are not resilient against AKC. We implement a concrete AKC attack on the mutually authenticated TLS protocol.

This is joint work with Marko Horvat and David Basin.

Speaker: Gildas Avoine
Title: Cracking Passwords with Time-memory Trade-offs
Abstract: Cryptanalytic time-memory trade-offs were introduced by Hellman in 1980 in order to perform key-recovery attacks on cryptosystems. A major advance was presented at Crypto 2003 by Oechslin, with the rainbow tables that outperform Hellman's seminal work. After introducing the cryptanalytic time-memory trade-offs, we will present in this talk a new variant, known as rainbow tables with fingerprints, which drastically reduce the number of false alarms during the attack. The key point of the technique consists in storing in the tables the fingerprints of the chains instead of their endpoints. The rainbow tables with fingerprints provide a time-memory trade-off that is about two times faster than the rainbow tables on usual problem sizes. We will illustrate the performance of the variant by cracking Windows NTLM Hash Passwords.

Speaker: David Modic
Title: Reading this May Harm Your Computer: The Psychology of Malware Warnings
Abstract: Internet users face large numbers of security warnings, which they mostly ignore. To improve risk communication, warnings must be fewer but better. We report an experiment on whether compliance can be increased by using some of the social-psychological techniques the scammers themselves use, namely appeal to authority, social compliance, concrete threats and vague threats. We also investigated whether users turned off browser malware warnings (or would have, had they known how).

Speaker: Alexandre Viejo
Title: Preserving the User's Privacy in Web Search Engines
Abstract: Web search engines (WSEs) use search queries submitted by users to profile them and to provide personalized services such as query disambiguation or query refinement. On the one hand, these services are valuable for the users because they get an enhanced web search experience. On the other hand, the compiled user profiles may contain sensitive information which might represent a serious privacy threat. The scientific community has acknowledged this problem and several privacy-preserving techniques which try to prevent this situation can be found in the literature. In this talk, we will discuss the advantages and shortcomings of the main proposals in this field and we will also introduce our different contributions.

Speaker: Jaap A. Kaandorp
Title: Modelling gene regulation of early development and cell movement in the sea anemone Nematostella vectensis
Abstract: We have developed a method to analyze spatio-temporal gene expression patterns (in situ hybridizations) and morphological data (based on confocal light microscopy images) of Nematostella during early embryonal development. The gene expression images are processed with two-dimensional geometry extraction methods and cell-layer decomposition methods to consistently compare and model the expression patterns. Moreover, a three-dimensional tool has been developed for geometry extraction and decomposition and to model expression patterns that are not radially symmetric about the main body axis. The model parameters and the gene network are inferred from the expression data using an optimization algorithm (e.g evolutionary algorithms and scatter search). In Nematostella vectensis cell migration is relevant and we need to include moving cells in a spatio-temporal model of gene regulation. Cell shape and movement is modelled in three dimensions using a cell boundary dynamics model and this model is coupled to the spatio-temporal model of gene regulation.

Speaker: Wojtek Jamroga
Title: Defendable Security in Interaction Protocols
Abstract:
We study the security of interaction protocols when incentives of participants are taken into account. We begin by formally defining correctness of a protocol, given a notion of rationality and utilities of participating agents. Based on that, we propose how to assess security when the precise incentives are unknown. Then, the security level can be defined in terms of defender sets, i.e., sets of participants who can effectively "defend" the security property as long as they are in favor of the property. In terms of technical results, we present a theoretical characterization of defendable protocols under Nash equilibrium, and study the computational complexity of related decision problems.

The talk will present joint work with Matthijs Melissen and Henning Schnoor.

Speaker: Rolando Trujillo
Title: Relay attacks and distance bounding protocols
Abstract: Distance bounding emerged as a countermeasure to relay attacks, which affects several technologies such as RFID, NFC, Bluetooth, and Ad-hoc networks. A relay attack, also known as mafia fraud, is a man-in-the-middle attack aimed at successfully passing an authentication protocol by cheating on the actual distance between the prover and the verifier. With the widespread deployment of contactless technologies in recent years, relay attacks has re-emerged as a serious security threat for authentication schemes. The aim of this talk is twofold: i) Introducing relay attacks and its most popular countermeasure, the distance bounding protocols. ii) Challenging the audience with interesting open problems in this subject.

Speaker: James Davenport
Title: The Security-Privacy tension: recent developments in the U.K. and elsewhere
Abstract: Concerns about the privacy of eletronically-transmitted information have been with us since the invention of the telephone exchange. At the National Security level, the Snowden revelations, and the largely ill-informed comment around them, has confused the debate. Irrespective of this issue, though, the public holds mutually contradictory views. Certain crimes (notably possession os paedophilic images) should be pursued and punished at all costs, but electronic information should be totally private. "But that's a different case" is a popular argument that does not work: technology doesn't have motives. This talk will examine the confused nature of the debate in the U.K. and certain international fora.

Speaker: Jurlind Budurushi
Title: A systematic approach for identifying all possibilities for casting a valid/invalid vote for local elections in Hesse by using the EasyVote system
Abstract: The first part of this talk gives an overview of the state of the art regarding the EasyVote system, which has been introduced for supporting voters in the vote casting phase and poll workers in the tallying phase in elections with complicated ballot papers, like the local elections in the state of Hesse. As the electoral regulations for casting a valid vote are very complicated, the second part of this talk presents a systematic approach to identify all possibilities to cast a valid/invalid vote (use cases). For future work the use cases identified will be tested on a prototype based on EasyVote that has been developed within a master thesis.

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Contact

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