Publications
Latest publications
A Federated Explainable AI Model for Breast Cancer Classification
Breast cancer diagnosis is a crucial domain where Explainable Artificial Intelligence (XAI) integration holds immense importance. Understanding AI model decisions not only enhances trust but also aids in…
Advancing elderly social care dropout prediction with federated learning: client selection and imbalanced data management
Accurate prediction of user dropout is crucial for enhancing the effectiveness of social care applications developed for the elderly. Given the sensitive nature of healthcare data, this study…
All publications
A Federated Explainable AI Model for Breast Cancer Classification
European Interdisciplinary Cybersecurity Conference · pp. 194-201 · 2024
Breast cancer diagnosis is a crucial domain where Explainable Artificial Intelligence (XAI) integration holds immense importance. Understanding AI model decisions not only enhances trust but also aids in treatment strategies. However, the need for…
Advancing elderly social care dropout prediction with federated learning: client selection and imbalanced data management
Cluster Computing · Vol. 28 · No. 2 · 2024
Accurate prediction of user dropout is crucial for enhancing the effectiveness of social care applications developed for the elderly. Given the sensitive nature of healthcare data, this study introduces a Federated Learning (FL) approach…
Carbon-Aware Machine Learning: A Case Study on Cellular Traffic Forecasting with Spiking Neural Networks
IFIP Advances in Information and Communication Technology · pp. 178-191 · 2024
Data management in Ethereum DApps: A cost and performance analysis
Future Generation Computer Systems · Vol. 153 · pp. 193-205 · 2024
The cost of interacting with a blockchain and the time required to search and retrieve information from it are important factors in the design of Decentralized Applications (DApps). The corresponding approaches for data management…
Federated learning for 5G base station traffic forecasting
Computer Networks · Vol. 235 · pp. 109950 · 2023
Cellular traffic prediction is of great importance on the path of enabling 5G mobile networks to perform intelligent and efficient infrastructure planning and management. However, available data are limited to base station logging information.…
Federated Learning for Early Dropout Prediction on Healthy Ageing Applications
2023 Eighth International Conference on Fog and Mobile Edge Computing (FMEC) · pp. 135-142 · 2023
The provision of social care applications is crucial for elderly people to improve their quality of life and enables operators to provide early interventions. Accurate predictions of user dropouts in healthy ageing applications are…
FedPOIRec: Privacy-preserving federated poi recommendation with social influence
Information Sciences · Vol. 623 · pp. 767-790 · 2023
With the growing number of Location-Based Social Networks, privacy-preserving point-of-interest (POI) recommendation has become a critical challenge when helping users discover potentially interesting new places. Traditional systems take a centralized approach that requires the…
Intelligent Client Selection for Federated Learning using Cellular Automata
arXiv · 2023
Federated Learning (FL) has emerged as a promising solution for privacy-enhancement and latency minimization in various real-world applications, such as transportation, communications, and healthcare. FL endeavors to bring Machine Learning (ML) down to the…
Predicting Early Dropouts of an Active and Healthy Ageing App
arXiv · 2023
In this work, we present a machine learning approach for predicting early dropouts of an active and healthy ageing app. The presented algorithms have been submitted to the IFMBE Scientific Challenge 2022, part of…
Towards Energy-Aware Federated Traffic Prediction for Cellular Networks
arXiv · 2023
Cellular traffic prediction is a crucial activity for optimizing networks in fifth-generation (5G) networks and beyond, as accurate forecasting is essential for intelligent network design, resource allocation and anomaly mitigation. Although machine learning (ML)…
Blockchain Applications in Agriculture: A Scoping Review
Applied Sciences · Vol. 12 · No. 16 · pp. 8061 · 2022
Blockchain is a distributed, immutable ledger technology initially developed to secure cryptocurrency transactions. Following its revolutionary use in cryptocurrencies, blockchain solutions are now being proposed to address various problems in different domains, and it…
Federated Neural Collaborative Filtering
Knowledge-Based Systems · Vol. 242 · pp. 108441 · 2022
In this work, we present a federated version of the state-of-the-art Neural Collaborative Filtering (NCF) approach for item recommendations. The system, named FedNCF, enables learning without requiring users to disclose or transmit their raw…
HFabD+M: A Web-based Platform for Automated Hyperledger Fabric Deployment and Management
2022 IEEE 1st Global Emerging Technology Blockchain Forum: Blockchain & Beyond (iGETblockchain) · pp. 1-6 · 2022
Hyperledger Fabric is an open-source private permissioned blockchain that supports the use of smart contracts (chaincode). It is aimed mainly at private networks of companies. To serve the different needs of each company and…
About Weighted Random Sampling in Preferential Attachment Models
arXiv · 2021
The Barabási-Albert model is a popular scheme for creating scale-free graphs but has been previously shown to have ambiguities in its definition. In this paper we discuss a new ambiguity in the definition of…
An Exact, Linear Time Barabási-Albert Algorithm
arXiv · 2021
This paper presents the development of a new class of algorithms that accurately implement the preferential attachment mechanism of the Barabási-Albert (BA) model to generate scale-free graphs. Contrary to existing approximate preferential attachment schemes,…
Exploring Ethereum’s Data Stores: A Cost and Performance Comparison
2021 3rd Conference on Blockchain Research & Applications for Innovative Networks and Services (BRAINS) · pp. 53-60 · 2021
The cost of using a blockchain infrastructure as well as the time required to search and retrieve information from it must be considered when designing a decentralized application. In this work, we examine a…
Lexicographic Enumeration of Set Partitions
arXiv · 2021
In this report, we summarize the set partition enumeration problems and thoroughly explain the algorithms used to solve them. These algorithms iterate through the partitions in lexicographic order and are easy to understand and…
Point-of-interest lists and their potential in recommendation systems
Information Technology & Tourism · Vol. 23 · No. 2 · pp. 209-239 · 2021
Location based social networks, such as Foursquare and Yelp, have inspired the development of novel recommendation systems due to the massive volume and multiple types of data that their users generate on a daily…
A Twitter-based approach of news media impartiality in multipartite political scenes
Social Network Analysis and Mining · Vol. 10 · No. 1 · 2020
News dissemination in the modern world deploys online social networks (OSNs) to instantly and freely convey facts and opinions to Internet users worldwide. Recent research studies the structure of the graph formed by the…
Revealing the political affinity of online entities through their Twitter followers
Information Processing & Management · Vol. 57 · No. 2 · pp. 102172 · 2020
In this work, we show that the structural features of the Twitter online social network can divulge valuable information about the political affinity of the participating nodes. More precisely, we show that Twitter followers…
How much does a zero-permission Android app know about us?
Proceedings of the Third Central European Cybersecurity Conference · pp. 1-5 · 2019
Android devices contain a vast amount of personal data of their owners. These data are stored on the device and are protected by the Android permission scheme. Android apps can obtain access to specific…
A Blockchain-Based Notarization Service for Biomedical Knowledge Retrieval
Computational and Structural Biotechnology Journal · Vol. 16 · pp. 288-297 · 2018
Biomedical research and clinical decision depend increasingly on scientific evidence realized by a number of authoritative databases, mostly public and continually enriched via peer scientific contributions. Given the dynamic nature of biomedical evidence data…
Communicating Personalized Risk Factors for Lifestyle Coaching
Proceedings of the 11th International Joint Conference on Biomedical Engineering Systems and Technologies · pp. 571-578 · 2018
Chronic non-communicable diseases such as diabetes, chronic cardiorenal and respiratory disease and cancer, are serious, burdensome and costly conditions that share a common characteristic: they heavily depend on common behavioural risk factors, such as…
Deriving the Political Affinity of Twitter Users from Their Followers
2018 IEEE Intl Conf on Parallel & Distributed Processing with Applications, Ubiquitous Computing & Communications, Big Data & Cloud Computing, Social Computing & Networking, Sustainable Computing & Communications (ISPA/IUCC/BDCloud/SocialCom/SustainCom) · pp. 1175-1182 · 2018
In this work, we show that Twitter users can reveal valuable political information about particular Nodes of Interest (NOIs) they opt to follow. More precisely, we utilize an interesting graph projection method and a…
Formal analysis of DeGroot Influence Problems using probabilistic model checking
Simulation Modelling Practice and Theory · Vol. 89 · pp. 144-159 · 2018
DeGroot learning is a model of opinion diffusion and formation in a social network. We examine the behaviour of the DeGroot learning model when external strategic players that aim to influence the opinion formation…
Privacy leakages about political beliefs through analysis of Twitter followers
Proceedings of the 22nd Pan-Hellenic Conference on Informatics · pp. 16-21 · 2018
In this paper, we focus on privacy leakages about Twitter users and show that simply establishing follower and friend connections in the Twitter network might be enough to reveal sensitive information about the political…
Notarization of Knowledge Retrieval from Biomedical Repositories Using Blockchain Technology
IFMBE Proceedings · pp. 69-73 · 2017
Biomedical research and clinical decision depend increasingly on a number of authoritative databases, mostly public and continually enriched via peer scientific contributions. Given the dynamic nature of data and their usage in the sensitive…
Privacy-Enhanced Television Audience Measurements
ACM Transactions on Internet Technology · Vol. 17 · No. 1 · pp. 1-29 · 2017
Internet-enabled television systems (SmartTVs) are a development that introduces these devices into the interconnected environment of the Internet of Things. We propose a privacy-preserving application for computing Television Audience Measurement (TAM) ratings. SmartTVs communicate…
A Privacy-by-Design Contextual Suggestion System for Tourism
Journal of Sensor and Actuator Networks · Vol. 5 · No. 2 · pp. 10 · 2016
We focus on personal data generated by the sensors and through the everyday usage of smart devices and take advantage of these data to build a non-invasive contextual suggestion system for tourism. The system,…
Implementing PacketEconomy: Distributed money‐based QoS in OMNET++
International Journal of Communication Systems · Vol. 30 · No. 11 · 2016
SummaryIn this work we examine how quality of service (QoS) can be achieved in a real network by allowing packets to coordinate using fiat money in a market economy for router queue positions. In…
Malevolent app pairs
Proceedings of the ACM International Conference on Computing Frontiers · pp. 431-436 · 2016
Portable smart devices potentially store a wealth of information of personal data, making them attractive targets for data exfiltration attacks. Permission based schemes are core security controls for reducing privacy and security risks. In…
Prince: an effective router mechanism for networks with selfish flows
Journal of Internet Engineering · Vol. 6 · No. 1 · pp. 355--362 · 2016
Starting from the premise that modern routers are not protected from aggressive and unresponsive flows, we define a new, almost stateless, active queue management scheme, called Prince. The basic idea is to protect the…
Privacy-preserving, user-centric VoIP CAPTCHA challenges
Information & Computer Security · Vol. 24 · No. 1 · pp. 2-19 · 2016
Purpose – This work aims to argue that it is possible to address discrimination issues that naturally arise in contemporary audio CAPTCHA challenges and potentially enhance the effectiveness of audio CAPTCHA systems by adapting…
Solving Influence Problems on the DeGroot Model with a Probabilistic Model Checking Tool
Proceedings of the 20th Pan-Hellenic Conference on Informatics · pp. 1-6 · 2016
DeGroot learning is a model of opinion diffusion and formation in a social network of individuals. We examine the behavior of the DeGroot learning model when external strategic players that aim to bias the…
Towards Privacy by Design in Personal e-Health Systems
Proceedings of the 9th International Joint Conference on Biomedical Engineering Systems and Technologies · pp. 472-477 · 2016
Personal e-health systems are the next generation of e-health applications and their goal is to assist patients in managing their disease and to help both patients and healthy people maintain behaviours that promote health.…
Interoperable Multimedia Annotation and Retrieval for the Tourism Sector
Communications in Computer and Information Science · pp. 65-76 · 2015
The Atlas Metadata System (AMS) employs semantic web annotation techniques in order to create an interoperable information annotation and retrieval platform for the tourism sector. AMS adopts state-of-the-art metadata vocabularies, annotation techniques and semantic…
Pythia: A Privacy-Enhanced Personalized Contextual Suggestion System for Tourism
2015 IEEE 39th Annual Computer Software and Applications Conference · 2015
We present Pythia, a privacy-enhanced non-invasive contextual suggestion system for tourists, with important architectural innovations. The system offers high quality personalized recommendations, non-invasive operation and protection of user privacy. A key feature of Pythia…
Reengineering the user: privacy concerns about personal data on smartphones
Information & Computer Security · Vol. 23 · No. 4 · pp. 394-405 · 2015
Purpose – This paper aims to discuss the privacy and security concerns that have risen from the permissions model in the Android operating system, along with two shortcomings that have not been adequately addressed.…
Social network analysis of public lists of POIs
Proceedings of the 19th Panhellenic Conference on Informatics · pp. 61-62 · 2015
In this work, we show how social network analysis can be applied to lists of points of interest (POIs) in order to extract important information about the POIs and the relations between them. More…
Versatile Query Scrambling for Private Web Search
Information Retrieval Journal · Vol. 18 · No. 4 · pp. 331-358 · 2015
We consider the problem of privacy leaks suffered by Internet users when they perform web searches, and propose a framework to mitigate them. In brief, given a ‘sensitive’ search query, the objective of our…
A game-theoretic analysis of preventing spam over Internet Telephony via audio CAPTCHA-based authentication
Journal of Computer Security · Vol. 22 · No. 3 · pp. 383-413 · 2014
Spam over Internet Telephony (SPIT) is a potential source of disruption in Voice over IP (VoIP) systems. The use of anti-SPIT mechanisms, such as filters and audio CAPTCHA (Completely Automated Public Turing Test to…
A novel mechanism for anonymizing Global System for Mobile Communications calls using a resource‐based Session Initiation Protocol community network
Security and Communication Networks · Vol. 8 · No. 3 · pp. 486-500 · 2014
Considering the widespread adoption of smartphones in mobile communications and the well‐established resource sharing use in the networking community, we present a novel mechanism to achieve anonymity in the Global System for Mobile Communications…
myVisitPlanner GR: Personalized Itinerary Planning System for Tourism
Lecture Notes in Computer Science · pp. 615-629 · 2014
This application paper presents myVisitPlannerGR, an intelligent web-based system aiming at making recommendations that help visitors and residents of the region of Northern Greece to plan their leisure, cultural and other activities during their…
Personalised Cloud-Based Recommendation Services for Creative Tourism
HTHIC 2014 · pp. 261 · 2014
Privacy-preserving computation of participatory noise maps in the cloud
Journal of Systems and Software · Vol. 92 · pp. 170-183 · 2014
This paper presents a privacy-preserving system for participatory sensing, which relies on cryptographic techniques and distributed computations in the cloud. Each individual user is represented by a personal software agent, deployed in the cloud,…
User-centric privacy-preserving statistical analysis of ubiquitous health monitoring data
Computer Science and Information Systems · Vol. 11 · No. 2 · pp. 525-548 · 2014
In this paper, we propose a user-centric software architecture for managing Ubiquitous Health Monitoring Data (UHMD) generated from wearable sensors in a Ubiquitous Health Monitoring System (UHMS), and examine how these data can be…
A Versatile Tool for Privacy-Enhanced Web Search
Lecture Notes in Computer Science · pp. 368-379 · 2013
We consider the problem of privacy leaks suffered by Internet users when they perform web searches, and propose a framework to mitigate them. Our approach, which builds upon and improves recent work on search…
DUTH at TREC 2013 Contextual Suggestion Track
Text Retrieval Conference · 2013
In this report we give an overview of our participation in the TREC 2013 Contextual Suggestion Track. We present an approach for context processing that comprises a newly designed and fine-tuned POI (Point Of…
Money-Based Coordination of Network Packets
Lecture Notes in Computer Science · pp. 197-208 · 2013
In this work, we apply a common economic tool, namely money, to coordinate network packets. In particular, we present a network economy, called PacketEconomy, where each flow is modeled as a population of rational…
A Framework for Anonymizing GSM Calls over a Smartphone VoIP Network
IFIP Advances in Information and Communication Technology · pp. 543-548 · 2012
The proposed framework describes a service for users that gives them the ability to make gsm calls from their smartphones without revealing their identity. The principle to achieve that is simple: instead of using…
A Privacy-Preserving Cloud Computing System for Creating Participatory Noise Maps
2012 IEEE 36th Annual Computer Software and Applications Conference · pp. 581-586 · 2012
Participatory sensing is a crowd-sourcing technique which relies both on active contribution of citizens and on their location and mobility patterns. As such, it is particularly vulnerable to privacy concerns, which may seriously hamper…
A query scrambler for search privacy on the internet
Information Retrieval · Vol. 16 · No. 6 · pp. 657-679 · 2012
We propose a method for search privacy on the Internet, focusing on enhancing plausible deniability against search engine query-logs. The method approximates the target search results, without submitting the intended query and avoiding other…
An efficient privacy-preserving solution for finding the nearest doctor
Personal and Ubiquitous Computing · Vol. 18 · No. 1 · pp. 75-90 · 2012
In this work, we define the Nearest Doctor Problem for finding the nearest doctor in case of an emergency and present a privacy-preserving protocol for solving it. The solution is based on cryptographic primitives…
On Money as a Means of Coordination between Network Packets
arXiv · Vol. 14 · No. 1 · 2012
In this work, we apply a common economic tool, namely money, to coordinate network packets. In particular, we present a network economy, called PacketEconomy, where each flow is modeled as a population of rational…
Privacy-Preserving Television Audience Measurement Using Smart TVs
IFIP Advances in Information and Communication Technology · pp. 223-234 · 2012
Internet-enabled television systems, often referred to as Smart TVs, are a new development in television and home entertainment technologies. In this work, we propose a new, privacy-preserving, approach for Television Audience Measurement (TAM), utilizing…
User-centric, privacy-preserving adaptation for voIP CAPTCHA challenges
Proceedings of the 6th International Symposium on Human Aspects of Information Security and Assurance, HAISA 2012 · 2012
The effectiveness of CAPTCHA challenges largely depends on being simultaneously easier to solve for humans and harder to solve for bots. In this work we argue that it is possible to enhance the effectiveness…
Using Personal Portfolios to Manage Customer Data
Lecture Notes in Computer Science · pp. 141-154 · 2012
Transactions today are conducted in a way that leaves no real option to the customers to protect their privacy. Sensitive private information is left uncontrolled at the companies’ disposal and is often (un)intentionally leaked…
An Exact and O(1) Time Heaviest and Lightest Hitters Algorithm for Sliding-Window Data Streams
2011 Fifth FTRA International Conference on Multimedia and Ubiquitous Engineering · pp. 89-94 · 2011
In this work we focus on the problem of finding the heaviest-k and lightest-k hitters in a sliding window data stream. The most recent research endeavours have yielded an e-approximate algorithm with update operations…
Enhancing Deniability against Query-Logs
Lecture Notes in Computer Science · pp. 117-128 · 2011
We propose a method for search privacy on the Internet, focusing on enhancing plausible deniability against search engine query-logs. The method approximates the target search results, without submitting the intended query and avoiding other…
Privacy-enhanced management of ubiquitous health monitoring data
Proceedings of the 4th International Conference on PErvasive Technologies Related to Assistive Environments · pp. 1-4 · 2011
In this paper, we propose a new architecture for managing data in a Ubiquitous Health Monitoring System (UHMS). The purpose of this architecture is to enhance the privacy of patients and furthermore to decongest…
Privacy-Preserving Statistical Analysis on Ubiquitous Health Data
Lecture Notes in Computer Science · pp. 24-36 · 2011
In this work, we consider ubiquitous health data generated from wearable sensors in a Ubiquitous Health Monitoring System (UHMS) and examine how these data can be used within privacy- preserving distributed statistical analysis. To…
(α, β) Fibonacci Search
arXiv · 2010
Knuth [12, Page 417] states that "the (program of the) Fibonaccian search technique looks very mysterious at first glance" and that "it seems to work by magic". In this work, we show that there…
A privacy-preserving protocol for finding the nearest doctor in an emergency
Proceedings of the 3rd International Conference on PErvasive Technologies Related to Assistive Environments · pp. 1-8 · 2010
In this work, we define the Nearest Doctor Problem (NDP) for finding the closest doctor in case of an emergency and present a secure multi-party computation for solving it. The solution is based on…
Economics of Personal Data Management: Fair Personal Information Trades
Next Generation Society. Technological and Legal Issues · pp. 151--160 · 2010
Individuals today have no control over the way their personal information is being used even though they are the ones to suffer the consequences of any unwanted uses of their information. We propose addressing…
Weighted Random Sampling over Data Streams
arXiv · 2010
In this work, we present a comprehensive treatment of weighted random sampling (WRS) over data streams. More precisely, we examine two natural interpretations of the item weights, describe an existing algorithm for each case…
Window-games between TCP flows
Theoretical Computer Science · Vol. 411 · No. 31 · pp. 2798--2817 · 2010
We consider network congestion problems between TCP flows and define a new game, the Window-game, which models the problems of network congestion caused by the competing flows. Analytical and experimental results show the relevance…
Probing based load balancing for web server farms
Proc. of the 13th Panhellenic Conference on Informatics · pp. 175--180 · 2009
We present an adaptive load balancing algorithm, ALBL, for cluster-based web systems. The balancing policy is based on two criteria; HTTP process time and network delay. The former describes web server ability to process…
Towards privacy in personal data management
Information Management & Computer Security · Vol. 17 · No. 4 · pp. 311-329 · 2009
PurposeIn order to enhance privacy protection during electronic transactions, the purpose of this paper is to propose, develop, and evaluate a personal data management framework called Polis that abides by the following principle: every…
The complexity of linear programming in -form
Information Processing Letters · Vol. 105 · No. 5 · pp. 199-201 · 2008
Linear programming in (γ,κ)-form is a restricted class of linear programming (LP) introduced in [L. Trevisan, Parallel approximation algorithms by positive linear programming. Algorithmica 21 (1998) 72–88]. Since [L. Trevisan, Erratum: A correction to…
Window-Games between TCP Flows
Lecture Notes in Computer Science · pp. 95-108 · 2008
We consider network congestion problems between TCP flows and define a new game, the Window-game, which models the problem of network congestion caused by the competing flows. Analytical and experimental results show the relevance…
Existence, uniqueness and asymptotic behavior of the solutions of a fuzzy differential equation with piecewise constant argument
Information Sciences · Vol. 177 · No. 18 · pp. 3855-3870 · 2007
In this paper we study the existence, the uniqueness and the asymptotic behavior of the solutions of the fuzzy differential equation of the form:x′(t)=px(t)+qx([t]),t∈[0,∞),where p, q are constant real numbers and the initial value…
Secure Mobile Database Applications: A Case Study
Theoretical Computer Science · Vol. 359 · No. 1-3 · pp. 400-417 · 2007
We examine the problem of assigning n independent jobs to m unrelated parallel machines, so that each job is processed without interruption on one of the machines, and at any time, every machine processes…
Weighted random sampling with a reservoir
Information Processing Letters · Vol. 97 · No. 5 · pp. 181-185 · 2006
In this work, a new algorithm for drawing a weighted random sample of size m from a population of n weighted items, where m⩽n, is presented. The algorithm can generate a weighted random sample…
Combinatorial Randomized Rounding: Boosting Randomized Rounding with Combinatorial Arguments
Applied Optimization · pp. 31-53 · 2001
Randomized Rounding (RR) is a simple and very efficient probabilistic method to convert a solution of a relaxed combinatorial optimization (CO) problem into an approximate solution to the original problem. Since its introduction by…
The Lagrangian Search Method
Nonconvex Optimization and Its Applications · pp. 283-294 · 2001
In this work, the Lagrangian Search Method (LSM), an algorithmic framework based on lagrangian relaxation, relaxed decision procedures and binary search, is presented. LSM is used to efficiently extend the class of positive linear…
Positive Linear Programming Extensions: Parallel Complexity and Applications
Lecture Notes in Computer Science · pp. 456-460 · 2000
In this paper, we propose a general class of linear programs that admit efficient parallel approximations and use it for efficient parallel approximations to hard combinatorial optimization problems.
Fast parallel approximations to positive linear programs with a small number of constraint violations
Technical Report TR99. 04.02, Computer Technology Institute · 1999
Very fast, sequential and parallel, approximations to hard combinatorial optimization problems
Technical Report TR99. 06.01, Computer Technology Institute · 1999
Parallel text retrieval on a high performance supercomputer using the Vector Space Model
Proceedings of the 18th annual international ACM SIGIR conference on Research and development in information retrieval - SIGIR '95 · pp. 58-66 · 1995
This paperl discusses the efi-iciency of a parallel text retrieval system that is based on the Vector Space Model.Specifically, we describe a general parallel retrieval algorithm for use with this model, the application of…