Blockchains

Public procurement tenders in Bulgaria are in the focus of public attention, despite the transparency of the process, which is conducted online through the Public Procurement Agency platform, participants require greater trust in the conduct of the procedures themselves, as they are not yet fully automated. Blockchain solutions are used in a wide range of businesses, as they offer transparency of transactions, trust between parties and data immutability and also seem suitable for conducting e-tenders for public procurement. This publication offers a solution based on a private blockchain HyperLedger Fabric, which in terms of structure and functionality builds on the existing solution. It ensures bidder identities are confidential from the unauthorized participants and transparency of the work of administrators in the platform and their actions when changing the status of a public procurement. The proposed blockchain based solution improves the evaluation process, reducing certain technical and human-error risks. The results show that it provides greater transparency and efficiency in the spending of public funds, achieving the set quantitative indicators with automated evaluation and qualitative factors defined in the smart contract.

Blockchain-based infrastructures have increasingly been adopted for secure and tamper-resistant management of academic credentials. Despite the advantages offered by blockchain technology, existing blockchain-based credential management systems continue to face several scalability challenges, particularly in terms of limited transaction throughput, increased confirmation delays, and continuous ledger growth resulting from storing individual certificates as separate blockchain transactions. These limitations become more evident in large-scale educational environments where universities and affiliated institutions are required to issue and verify thousands of digital credentials within limited operational timeframes. To overcome these challenges, this work introduces a performance-optimized blockchain architecture for scalable academic credential management. The proposed framework separates certificate preprocessing from blockchain anchoring by incorporating a microservice-based parallel processing layer, Merkle-tree-based batch anchoring, and distributed off-chain storage mechanisms. This modular design reduces blockchain transaction overhead while maintaining the security, integrity, auditability, and verifiability of academic credentials. To assess system performance, a formal analytical model integrating queueing theory and blockchain performance characteristics is developed to characterize system behavior under varying workload conditions. By enabling multiple certificates to be aggregated and committed through a single blockchain transaction, the proposed architecture improves throughput and enhances storage efficiency compared to conventional blockchain-based approaches. Analytical evaluation demonstrates that the system can sustain high certificate issuance rates while maintaining low confirmation latency and minimal on-chain storage growth.

Despite significant advances in electronic voting technologies, voter accreditation in many electoral systems remains vulnerable to identity fraud, database tampering, equipment failure, and centralized security breaches. Existing accreditation solutions often rely on single-modal biometric authentication and centralized architectures, limiting their robustness, transparency, and public trust. This paper proposes a Blockchain-based Bimodal Voter Accreditation System (Block-BVAS), together with a practical framework for its deployment in electronic voting systems. The proposed system integrates multimodal biometric authentication using facial and fingerprint recognition with a private Ethereum blockchain and conventional cryptographic mechanisms to provide secure, tamper-resistant, and auditable voter accreditation to provide secure, decentralized, and tamper-resistant voter accreditation. A Raspberry Pi 5 serves as the embedded processing platform, demonstrating the feasibility of implementing the framework on cost-effective hardware. By combining distributed-ledger technology with encrypted biometric verification, the proposed architecture enhances the integrity, confidentiality, and immutability of election-related records while addressing limitations associated with single-factor authentication and conventional centralized record management. Experimental evaluation of the biometric authentication module performed effectively, with fingerprint recognition achieving an average authentication accuracy (AA) of 97.8% and facial recognition averaging 95.1%. The blockchain storage overhead (BSO) displayed a near-linear growth pattern relative to the number of transactions, consistent with theoretical expectations for blockchain architectures. Reliability analysis indicated system uptime exceeding 95%, with only minimal operational failures recorded during the test period. This blockchain implementation further demonstrated reliable transaction processing and secure record management, indicating the effectiveness of the proposed Block-BVAS in enhancing the security, transparency, and trustworthiness of electronic voter accreditation.