A Generic Sharding Scheme for Blockchain Protocols

TL;DR

This paper presents a formal, modular framework for blockchain sharding that guarantees safety and liveness, demonstrated through application to the Algorand protocol with a secure node assignment mechanism.

Contribution

It introduces a general, adaptable framework for blockchain sharding with proven safety and liveness guarantees, and demonstrates its application to Algorand.

Findings

Framework guarantees safety and liveness for sharded protocols

Application to Algorand demonstrates practical use

Secure node assignment mechanism resists adaptive adversaries

Abstract

This thesis introduces a formal general framework for scaling blockchain protocols by sharding. The framework is modular and it can be adjusted for different needs or sets of assumptions. We prove that sharded protocols obtained by following our scheme (with correct modules in place) live up to the same safety and liveness guarantees as their non-sharded counterparts. The proof is general and relies on well-defined specifications of certain components. This lays the ground for simple proofs of correctness for sharded protocols obtained by following the proposed scheme. The framework is not left as an obscure specification of some high level structure; explicit use is demonstrated by applying it to shard Algorand. As part of this concrete construction, a tamper-proof mechanism to assign nodes to shards is introduced. This mechanism is constructed by using verifiable random functions and can safely withstand a powerful adaptive adversary.