Designing layer-2 blockchain applications: methodologies and solutions

Blockchain technology original usage was proposed to support decentralized virtual payments, and it evolved into a global computing platform to support smart contracts. Blockchain technology ensures data and computation immutability and transparency, thus making any application based on blockchain publicly auditable. Nowadays, this technology is a key component of the next generation of the web, also known as Web3, composed of decentralized platforms and applications. However, the benefits of the blockchain do not come without drawbacks, such as low scalability, data cannot be concealed thus raising privacy issues, and a non trivial communication across distinct blockchains. This thesis dives deep into these drawbacks, and it analyzes the current solutions decoupling the operations between off-chain components and on-chain components. Such types of solutions are known in the literature as layer-2 because they outsource some operations off-chain, while their correctness is still ensured by the blockchain. Blockchain verifiability grants public auditability as a solely on-chain implementation would have benefited. This thesis proposes a methodology to guide the design of layer-2 solutions of blockchain decentralized applications. The methodology consists first of an analysis of the requirements of a blockchain application. Then, it proposes a three-steps workflow to structure the layer-2 application. The methodology is validated with three proof of concepts.