publications

2025

1. Preprint

   From Fragmented Systems to Transparent Governance: Blockchain-Enabled Water Management with IoT Integration

   Andreas Sendros, Periklis Kostamis, Ioannis Zikos, and 4 more authors

   Water Resources Management, Oct 2025

   ISSN: 2693-5015

   Abs DOI

   Aging urban water distribution networks face increasing pressure from growing demand and infrastructure deterioration, while the integration of IoT monitoring systems highlight the urgent need for innovative and sustainable solutions that enhance system reliability and ensure data security. At the same time, the fragmented nature of water governance creates further barriers to coordinated, transparent, and efficient water management. Our work aims to address these challenges by proposing a holistic architecture for a customized private permissioned blockchain network specifically designed for IoT-enabled water meters. This approach mitigates data breaches, ensures secure data sharing among IoT devices, and facilitates precise water usage measurements and real-time leak detection.To address these water management challenges, we developed an automated framework for the deployment, management, and updating of Hyperledger Fabric blockchains networks, specifically tailored for public utility services. The network leverages chaincodes to secure IoT data storage and analysis, effectively preventing unauthorized access and malicious actions. Furthermore, Ricardian Contracts are employed to ensure that decision-making processes align with the legal agreements between consumers and service providers, guaranteeing automatic regulatory compliance.The project’s architecture supports hierarchical data access, ensuring confidentiality and privacy across water management agencies, regulatory agencies, and data owners. A proof of concept has been successfully implemented across two Greek municipalities, involving five organizations and over 150 water meters.

2. Conference

   Bloom Filter Variations for Enhanced Log Search in Ethereum

   George Drakoulis, Andreas Sendros, Periklis Kostamis, and 1 more author

   In 2025 IEEE International Conference on Blockchain and Cryptocurrency (ICBC) (IEEE ICBC’25), Jun 2025

   Abs Code Poster

   Efficient data retrieval is a critical challenge for blockchain platforms as they scale. Ethereum leverages Bloom Filters to accelerate log retrieval by reducing computational overhead. However, the default Bloom Filter implementation introduces false positives and inefficiencies in handling the rapidly growing data size of the Ethereum blockchain. This paper explores Ethereum-specific variations of Bloom Filters to mitigate these limitations. We propose three optimized methods that take advantage of the unique characteristics of Ethereum logs and block structures, designed to minimize false positive rates, improve retrieval speed, and optimize storage requirements, with trade-offs between computational overhead and retrieval accuracy. Our evaluations demonstrate that these variations outperform standard Bloom Filters in Ethereum, contributing to the advancement of blockchain data structures.

3. Book Chapter

   Federated Learning for Recommender Systems: Advances and Perspectives

   Vasileios Perifanis, Nikolaos Pavlidis, Andreas Sendros, and 1 more author

   In Federated Learning Systems: Towards Privacy-Preserving Distributed AI, Jun 2025

   Abs DOI

   Federated Learning (FL) has emerged as a promising solution within recommender systems, driven by the growing user demand for privacy-centric design. FL not only meets privacy needs but also enables precise, personalized recommendations while reducing the exposure of user preferences and interactions to external servers without explicit consent. This chapter provides a comprehensive review of literature on the use of FL in recommendation applications to safeguard user privacy. It highlights several groundbreaking methods that have transformed federated recommender systems. These include the use of cryptographic techniques to protect against private information leakage from adversarial attacks, the adoption of blockchain architectures for decentralization, and the implementation of graph-based models to better understand complex user-item interactions, thereby improving recommendation accuracy. The chapter discusses the horizon of FL in recommendation systems, examining open problems and limitations. This exploration casts a light on the potential future directions and innovations that can further fortify the synergy between FL and recommender systems.

4. Journal

   Federated Learning for privacy-Friendly Health Apps: A Case Study on Ovulation Tracking

   Nikolaos Pavlidis, Andreas Sendros, Theodoros Tsiolakis, and 10 more authors

   Journal of Sensor and Actuator Networks, Feb 2025

   Number: 1 Publisher: Multidisciplinary Digital Publishing Institute

   Abs DOI Code Website

   In an era of increasing reliance on digital health solutions, safeguarding user privacy has emerged as a paramount concern. Health applications often need to balance advanced AI functionalities with sufficient privacy measures to ensure user engagement. This paper presents the architecture of FLORA, a privacy-first ovulation-tracking application that leverages federated learning (FL), privacy-enhancing technologies (PETs), and blockchain to protect user data while delivering accurate and personalized health insights. Unlike conventional centralized systems, FLORA ensures that sensitive information remains on users’ devices, with predictive algorithms powered by local computations. Blockchain technology provides immutable consent tracking and model update transparency, further improving user trust. In addition, FLORA’s design incentivizes participation through a token-based reward system, fostering collaborative data contributions. This work illustrates how the integration of cutting-edge technologies creates a secure, scalable, and user-centric health application, setting a new standard for privacy-preserving digital health platforms.

2024

1. Journal

   Data management in Ethereum DApps: A cost and performance analysis

   Periklis Kostamis, Andreas Sendros, and Pavlos S. Efraimidis

   Future Generation Computer Systems, Apr 2024

   Abs DOI Code

   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 in Ethereum vary from pure on-chain solutions to hybrid architectures. In this work, we thoroughly examine a wide range of data management methods, including unconventional ones, and evaluate them in terms of storage cost and retrieval latency while considering the impact of recent hard forks. More precisely, we elaborate on the use of Smart Contract (SC) storage as a data store for DApps and in view of the prohibitive cost inherent to this approach, we present and compare methods for low-cost data handling in Ethereum, namely the event-logs, the transaction payload, and the almost surprising exploitation of unused function arguments. In addition, we study hybrid schemes by using IPFS and Swarm as storage platforms and Ethereum as a timestamping proof mechanism. Such schemes are especially effective when large chunks of data have to be managed. The upload and retrieval performance of these platforms and the cost associated with storing (on-chain) the identifiers of the uploaded data are of utmost importance and therefore are investigated in detail.

2022

1. Conference

   HFabD+M: A Web-based Platform for Automated Hyperledger Fabric Deployment and Management

   Ioannis Zikos, Andreas Sendros, George Drosatos, and 1 more author

   In 2022 IEEE 1st Global Emerging Technology Blockchain Forum: Blockchain & Beyond (iGETblockchain), Nov 2022

   Abs DOI Code

   Hyperledger Fabric is an open-source private per-missioned blockchain that supports the use of smart contracts (chaincode). It is aimed mainly at private networks of compa-nies. To serve the different needs of each company and to be flexible in customer requirements, it consists of various adaptive components. Although this structure efficiently addresses a wide range of needs, deploying such a network for research purposes or rapid development is complex. In this paper, we present a web-based system architecture for the automated deployment of a Hyperledger Fabric network, and in addition, we describe the tools needed to manage and update such a network. Finally, as a proof-of-concept, we implement the proposed architecture to demonstrate the feasibility of our approach.

2. Journal

   Blockchain Applications in Agriculture: A Scoping Review

   Andreas Sendros, George Drosatos, Pavlos S. Efraimidis, and 1 more author

   Applied Sciences, Jan 2022

   Number: 16 Publisher: Multidisciplinary Digital Publishing Institute

   Abs DOI

   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 is currently one of the most “disruptive” technologies. This paper presents a scoping review of the scientific literature for exploring the current research area of blockchain applications in the agricultural sector. The aim is to identify the service areas of agriculture where blockchain is used, the blockchain technology used, the data stored in it, its combination with external databases, the reason it is used, and the variety of agricultural products, as well as the level of maturity of the respective approaches. The study follows the PRISMA-ScR methodology. The purpose of conducting these scoping reviews is to identify the evidence in this field and clarify the key concepts. The literature search was conducted in April 2021 using Scopus and Google Scholar, and a systematic selection process identified 104 research articles for detailed study. Our findings show that in the field, although still in the early stages, with the majority of the studies in the design phase, several experiments have been conducted, so a significant percentage of the work is in the implementation or piloting phase. Finally, our research shows that the use of blockchain in this domain mainly concerns the integrity of agricultural production records, the monitoring of production steps, and the monitoring of products. However, other varied and remarkable blockchain applications include incentive mechanisms, a circular economy, data privacy, product certification, and reputation systems. This study is the first scoping review in this area, following a formal systematic literature review methodology and answering research questions that have not yet been addressed.

2021

1. Conference

   Exploring Ethereum’s Data Stores: A Cost and Performance Comparison

   Periklis Kostamis, Andreas Sendros, and Pavlos Efraimidis

   In 2021 3rd Conference on Blockchain Research & Applications for Innovative Networks and Services (BRAINS), Sep 2021

   Abs DOI Video Code

   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 comprehensive set of data management approaches for Ethereum applications and assess the associated cost in gas as well as the retrieval performance. More precisely, we analyze the storage and retrieval of various-sized data, utilizing smart contract storage. In addition, we study hybrid approaches by using IPFS and Swarm as storage platforms along with Ethereum as a timestamping proof mechanism. Such schemes are especially effective when large chunks of data have to be managed. Moreover, we present methods for low-cost data handling in Ethereum, namely the event-logs, the transaction payload, and the almost surprising exploitation of unused function arguments. Finally, we evaluate these methods on a comprehensive set of experiments.