Author Archives: acadia

04/02/2020 – Talk by Vasileios Drakopoulos

Title: BIVARIATE FRACTAL INTERPOLATION SURFACES: THEORY AND APPLICATIONS
Time: 14:15
Location: Meeting Room B, Building Zeta
Speaker: Vasileios Drakopoulos
Abstract: Fractal interpolation offers an alternative to traditional interpolation techniques, aiming primarily at data which present detail at different scales or some degree of self-similarity. These characteristics, often intrinsic in natural objects, imply an irregular and non-smooth structure which is inconvenient to capture by elementary functions such as polynomials. 
Specifically, a fractal interpolation function, as defined by M. F. Barnsley and other researchers, can be considered as a continuous function whose graph is the attractor of an appropriately chosen iterated function system. If this graph, usually of non-integral dimension, belongs to the three-dimensional space and has Hausdorff – Besicovitch dimension between 2 and 3, then the resulting attractor is called fractal interpolation surface. 
During this talk, we discuss the theory and applications of fractal interpolation surfaces constructed by bivariate functions on rectangular grids. As far as the theory is concerned, we focus on two important issues: (a) The ensurance of continuity, which is in general a more complicated task than in the case of fractal interpolation functions on the plane, and (b) the identification of the vertical scaling factors which are the only free parameters in such a construction. As far as the applied part is concerned, we present several practical applications of fractal interpolation surfaces, including image compression, 3D data representation and medical imaging.

27/11/2019 – Talk by Carey Lee Williamson

Title: An Empirical Study of Campus-Level Instagram Traffic
Time: 13:00
Location: Meeting Room B, Building Zeta
Speaker: Carey Lee Williamson
Abstract: Instagram is a popular network application for photo sharing, video streaming, and online social media interaction. This talk presents results from an empirical study of Instagram network traffic, as viewed from a large campus edge network. Despite the challenges of NAT, DHCP, end-to-end encryption, and high traffic volume, we are able to identify key characteristics of Instagram traffic, which exceeds 1 TB per day. The main highlights from our study include classic observations such as diurnal usage patterns, Zipf-like distributions for IP frequency-rank profile, and heavy-tailed transfer size distributions. Several new observations include anomalous spikes in Instagram traffic, some network policies that inhibit Instagram usage, and some small differences in Instagram usage between campus-based users and the general public.

18/11/2019 – Talk by Benjamin Krumnow

Title: mashing OpenWPM for fun and profit
Time: 10:00
Location: Acadia Lab, Building Zeta
Type: Research talk
Speaker:  Hugo Jonker
Abstract: Web bots are a widely recognized tool to conduct empirical studies in the World Wide Web. OpenWPM is a framework that uses a web bot framework to facilitates web measurements. It is used in at least 46 scientific studies. However, there are clear indications that web sites attempt to recognize web bots and thereupon serve deviating content or block bots. Due to browser fingerprinting, this can already happen with the first call of a web page. For doing so, a web server attempts to retrieve unique properties that distinguish a web bot from human-controlled web browsers. To what extent OpenWPM is vulnerable to fingerprint-based detection has yet not been questioned. In this talk, I will present our investigation of detecting OpenWPM users based on their fingerprints. For that, we conduct a systematic analysis of the OpenWPM system architecture. We determine unique properties in OpenWPM’s fingerprint by applying fingerprinting and template attack tools for each component of OpenWPM. Our study reveals over 2K not-yet known properties, that would allow any web server to detect OpenWPM users. We show that most differences in OpenWPM result from automation components or the Firefox headless mode. Nevertheless, some deviations only occur in OpenWPM and could also be used to distinguish OpenWPM from ordinary bots. For demonstration purposes, we develop a web application that detects OpenWPM-based web clients and delivers manipulated content to them.

18/11/2019 – Talk by Hugo Jonker

Title: Shepherd – an automatic and large-scale study of website login security
Time: 9:30
Location: Acadia Lab, Building Zeta
Type: Research talk
Speaker:  Hugo Jonker
Abstract: Logging in on websites is common. However, it wasn’t always secure – as FireSheep showed dramatically in 2010. A malicious agent could simply eavesdrop on WiFi traffic and steal credentials of logged-in users. In response to FireSheep, major websites fixed their login security. However, it remains unclear whether others followed suit.Investigating this scientifically is fraught with challenges: acquiring passwords, automating logins on unknown websites, etc. In this talk, we present Shepherd, the result of a 2 year engineering effort to automate website logins. Moreover, we will present and discuss the results of a security scan with Shepherd, which showed that out of 7,113 sites where login was successful, 2,417 (34%) is still vulnerable to some variant on the FireSheep attack.

28/10/2019 – Talk by Silvia Crafa

Title: Smart contracts programming: formal methods in action
Time: 9:30
Location: Meeting Room B, Building Zeta
Type: Research talk
Speaker:  Silvia Crafa
Abstract:
In this talk I’ll focus on smart contracts in the Ethereum blockchain, discussing their motivations and  presenting their programming model. I’ll show how the theory of programming languages can be used in this new context to clarify the semantics of contracts written in the Solidity programming language. Moreover, I’ll show how the development of the type theory of the formalised core of Solidity revealed a type-safety issue in its compiler, and I’ll suggest a solution that might be reused in the more classical context of Object Oriented Languages.

19/09/2019 – Talk by Shantanu Das

Title: Patrolling on Dynamic Ring Networks
Time: 15:50
Location: Acadia Lab, Building Zeta
Type: Research talk
Speaker:  Shantanu Das
Abstract: 
We study the problem of patrolling the nodes of a network collaboratively by a team of mobile agents, such that each node of the network is visited by at least one agent once in every I(n) time units, with the objective of minimizing the idle time I(n). While patrolling has  been studied previously for static networks, we investigate the problem on dynamic networks with a fixed set of nodes, but dynamic edges. In particular, we consider 1-interval-connected ring networks and provide various patrolling algorithms for such networks, for k = 2 or k > 2 agents.  We also show almost matching lower bounds that hold even for the best starting configurations. Thus, our algorithms achieve close to optimal idle time. Further, we show a clear separation in terms of idle time, for agents that have prior knowledge of the dynamic networks compared to agents that do not have such knowledge. This paper provides the first known results for collaborative patrolling on dynamic graphs.

19/09/2019 – Talk by Euripdes Markou

Title: Exploring Graphs with Time Constraints by Unreliable Collections of Mobile Robots
Time: 15:15
Location: Acadia Lab, Building Zeta
Type: Research talk
Speaker:  Euripdes Markou
Abstract: 
A graph environment must be explored by a collection of mobile robots. Some of the robots, a priori unknown, may turn out to be unreliable. The graph is weighted and each node is assigned a deadline. The exploration is successful if each node of the graph is visited before its deadline by a reliable robot. The edge weight corresponds to the time needed by a robot to traverse the edge. Given the number of robots which may crash, is it possible to design an algorithm, which will always guarantee the exploration, independently of the choice of the subset of unreliable robots by the adversary? We find the optimal time, during which the graph may be explored. Our approach permits to find the maximal number of robots, which may turn out to be unreliable, and the graph is still guaranteed to be explored.
We concentrate on line graphs and rings, for which we give positive results. We start with the case of the collections involving only reliable robots. We give algorithms finding optimal times needed for exploration when the robots are assigned to fixed initial positions as well as when such starting positions may be determined by the algorithm. We extend our consideration to the case when some number of robots may be unreliable. Our most surprising result is that solving the line exploration problem with robots at given positions, which may involve crash-faulty ones, is NP-hard. The same problem has polynomial solutions for a ring and for the case when the initial robots’ positions on the line are arbitrary. The exploration problem is shown to be NP-hard for star graphs, even when the team consists of only two reliable robots.

13/12/2018 – Talk by Shantanu Das

Title: Exploration Algorithms for Energy Constrained Robots
Time: 13:00
Location: Meeting Room B, Building Zeta
Type: Research talk
Speaker:  Shantanu Das
Abstract: 
We consider a team of mobile robots moving on graph where each robot has a constraint on its energy consumption which limits the number of edges it can traverse. Under this constraint we look at the problem of graph exploration. Since any single robot may not completely explore the graph, the robots need to collaborate so that each node is visited by some robot. We consider three different optimization criteria: the size of the team, the energy budget per robot, and finally the number of nodes visited. We present efficient algorithms and prove lower bounds on these different measures of optimization. We also show a separation result between exploration with return and exploration without return.

30/11/2018 – Talk by Manali Chakraborty

Title: An Intelligent Framework for Managing Smart Power Grid
Time: 12:00
Location: Meeting Room B, Building Zeta
Type: Research talk
Speaker:  An Intelligent Framework for Managing Smart Power Grid
Abstract: 
The increasing dependability on the communication network makes Smart Grid vulnerable towards several cyber security threats. Advanced metering infrastructure (AMI) is arguably the most important and critical part of Smart Grid. AMI deals with the most sensitive information in the Grid and transmits them through the network. There already exist a good number of security solutions for AMI. However the percentage of security attacks is also increasing day by day and so does the innovative and intelligent ideas behind those attacks. As the inherent characteristics of Smart Grid is quite unique and different from traditional IT networks, the existing solutions fall short to handle these Smart Grid specific problems. Besides, balancing the supply-demand ratio in the Smart Grid considering all these odds, is far from being an easy job and requires additional technological support. Moreover, in order to maximize the benefits of Smart Grid, it is utmost important to connect and manage all the components and devices in the grid. This work in this thesis focuses on the feasibility of improving the security and autonomic functionalities of Advance Metering Infrastructure (AMI) in Smart Grid. The work can be broadly categorized into three parts depending on the concerned functionality of AMI.