ZeroSync: Validity Proofs to Bitcoin [pdf]

From Robin Linus, in bitcoin-dev mailing list:

We introduce ZeroSync, the first-ever proof system addressing Bitcoin’s scalability challenges with Succinct Non-Interactive Argument of Knowledge (SNARKs). ZeroSync compresses the entire Bitcoin blockchain into a compact proof of validity, enabling instant verification and unlocking various innovative applications. We discuss our prototype implementation of a chain state proof, utilizing the Cairo language, Utreexo, and recursive STARKs. Our work enables diverse applications, including quick bootstrapping of full nodes, trustless light clients, enhanced Lightning Network privacy, and secure cross-chain bridges. Chain state proofs require no consensus changes, which is crucial as forks in Bitcoin are challenging to implement and achieve consensus for. Despite the existing bottleneck of prover performance, we present a range of optimization strategies and demonstrate the practicality of generating a complete chain state proof. Finally, we introduce zkCoins, a client-side validation protocol combined with zeroknowledge SNARKs, drastically improving privacy and throughput of token transactions. In combination with future Bitcoin features, such as Simplicity, zkCoins also enables private and more scalable BTC transactions. The groundbreaking compression capabilities of SNARKs initiated a paradigm shift in cryptocurrency design, and ZeroSync is pioneering their application to Bitcoin.