Next-Generation Blockchain Systems: Innovations in Smart Contracts, Layer-2 Data Availability, Privacy-Preserving Compliance and Certification

The rapid digitalization of modern society has transformed how information is stored, transactions are executed, and trust is established in digital environments. Blockchain technology has emerged as a promising foundation for decentralized systems by providing immutability, transparency, and trustworthiness. Despite these advancements, real-world blockchain adoption reveals fundamental limitations. Smart contracts still lack modular and secure design patterns for managing complex access control requirements. Blockchain systems face scalability and data availability constraints, and the immutability of on-chain data often conflicts with regulatory compliance, such as the General Data Protection Regulation (GDPR). At the same time, blockchain-based certification systems must balance public verifiability with the privacy of sensitive information, a challenge that current approaches struggle to address. This thesis addresses these challenges by advancing the design of blockchain systems across multiple layers of the ecosystem. It introduces a hierarchical smart-contract design pattern that extends the traditional factory pattern with multirole authentication and authorization mechanisms. This approach enables contracts to be organized across hierarchical levels, ensuring that roles and permissions are consistently enforced, and improving scalability, governance, and security in decentralized applications that reflect real-world organizational structures. In addition, the thesis presents a decentralized data storage and retrieval framework that integrates blockchain technology with IPFS and cryptographic techniques. By storing cryptographic references on-chain and distributing encrypted data off-chain, the proposed framework ensures immutability, traceability, availability, and confidentiality while enabling efficient verification without exposing sensitive information. This design addresses limitations in managing large data volumes and supports privacy-preserving access in distributed environments. Scalability and data availability are further addressed through a comprehensive study of Layer 2 (L2) solutions and the development of a novel approach that leverages blob storage and adaptive multifactor scoring for rollup data. This solution balances scalability, efficiency, and security, ensuring transaction data remains accessible for independent verification while preserving trustless guarantees in high-throughput scenarios. To address the tension between blockchain immutability and data protection requirements, this thesis proposes an integrated framework combining on-chain and off-chain components with cryptographic techniques. The framework enables sensitive data to be managed in a manner that respects user rights, such as rectification and erasure, while maintaining auditability and accountability. In parallel, a privacy-preserving digital certification framework is presented that combines blockchain technology with zero-knowledge proofs and Merkle trees, enabling selective disclosure of certificate attributes and verification without accessing sensitive details. Taken together, these contributions provide a comprehensive response to key limitations hindering blockchain adoption. The thesis advances smart contract governance, decentralized data management, scalability, regulatory compliance, and certification mechanisms, strengthening the role of blockchain as a trustworthy, scalable, and privacy-aware infrastructure for real-world applications.