Reclaiming scalability and privacy in the decentralized setting

The advent of blockchains has expanded the horizon of possibilities to novel decentralised applications and protocols that were not possible before. Designing and building such applications, be it for offering new ways for humans to interact or for circumventing the shortcomings of existing blockchains, requires analysing their security with a rigorous and multi-faceted approach. Indeed, the attack surface of decentralised, trustless applications is vastly more expansive than that of classical, server-client-based ones. Desirable properties such as security, privacy and scalability are attainable via established and widely applied approaches in the centralised case, where clients can afford to trust third party servers. Is it possible though for clients to self organize and attain these properties in use cases of interest without reliance on central authorities? We examine this question in the setting of a variety of blockchain-based applications. With an explicit aim of improving the state of the art and extending the limits of possible decentralised operations with precision and robustness, the present thesis explores, builds, analyses, and improves upon payments, content curation and decision making