Toward a Fast and Secure Blockchain Framework for Smart Contracts

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Following the success of the cryptocurrencies, blockchain has recently evolved into a technology platform that powers secure, decentralized, and consistent transaction ledgers at Internet-scale. Smart contract deployment is the most important feature of many blockchain systems. Users can develop smart contracts to encode arbitrarily complicated transaction rules and deploy these contracts to a blockchain system. The contracts (i.e., transaction rules) are then faithfully executed and enforced by all participants of the system, eliminating any potential counter-party risk of the encoded transactions in future. One challenge for the adoption of smart contract techniques is the security risk. Because smart contracts are in fact programs that directly manipulate digital assets, ensuring the correctness of these contracts is very critical. Unfortunately, human programmers often make mistakes and errors. The consequence of programming errors and security vulnerabilities in smart contracts is particularly severe, often leading to tens of millions of dollar losses. Another challenge for the adoption is the performance issue. To ensure the consistency of the transaction ledger, the consensus protocols in blockchain systems have to operate with slow block generation to avoid concurrent blocks (i.e., forks), which are considered harmful for the consensus safety. Therefore these systems have very limited transaction throughputs for smart contracts. Users often have to wait for a long period of time to confirm a transaction. To tackle the security challenge, we propose to design a new set of tools for securing smart contracts, combining the static analysis with runtime instrumentations. One observation is that the transaction execution is not the bottleneck in blockchain platforms. The bottleneck is instead first at the consensus protocol and then at the blockchain storage layer. Therefore the overhead of runtime instrumentation, which is often too expensive for other domains, is in fact negligible for smart contracts. To tackle the performance challenge, we propose to design a novel consensus protocol that reorganizes blocks into direct acyclic graph to safely incorporate concurrent blocks. The protocol inherently encodes two strategies, an optimistic strategy for high performance and a conservative strategy that ensure the consensus progress to thwart liveness attacks. We also propose to revisit the design of the storage layer and the transaction propagation to build a high performance end-to-end blockchain platform. If the proposed research becomes successful, the proposed techniques would make the development of smart contracts significantly more secure. The techniques would also allow blockchain platforms to process smart contracts at a higher throughput and a faster speed. The ultimate goal of the proposed research is to find comprehensive solutions to unleash the full potential of smart contract technologies.