Formal Modeling and Verification of Block Production BABE Protocol in Polkadot

초록

Polkadot is an emerging blockchain application in the cryptocurrency ecosystem, where a large number of participants actively take part to earn rewards. Block production in Polkadot is one of the most critical and technically complex components, which is governed by the Blind Assignment for Blockchain Extension (BABE) protocol. In BABE, validators compete in time slots to produce blocks by following the longest chain rule. To determine the eligibility of a specific validator for a given slot, several sub-operations are performed, including block lottery execution, block authoring, and block building procedures. Even a minor flaw in these processes can adversely affect the correctness of the chain and may compromise the overall blockchain operation. To ensure a reliable and error-free system, rigorous formal verification is essential to mathematically guarantee system correctness and reliability. Existing studies mainly rely on informal testing or limited assertion-based validation, while a comprehensive formal verification of BABE is still missing. To bridge this gap, this work presents a formal verification of the BABE protocol using model checking techniques. For this purpose, an integrated behavioral model of BABE is developed using the Process Meta Language (Promela), in which each core operational aspect of the protocol is modeled in detail. After modeling, key safety and liveness properties, such as fairness, availability, integrity, and consistency, are formally specified using Linear Temporal Logic (LTL). Both the Promela model and the corresponding LTL specifications are provided as input to the model checker, which verifies the properties over all possible executions of the model. Additionally, verification results include an analysis of the explored state space, verification time, and memory consumption. This study contributes toward the formal verification of other major Polkadot protocols by demonstrating the applicability of model checking, specifically using the SPIN model checker.

키워드