Conclusions and References

Table of Links

Abstract and 1. Introduction

2. On-chain contracts
3. Off-chain contracts
4. Conclusions and References

4. Conclusions

We presented an optimistic protocol for the off-chain execution of Bitcoin smart contracts. Our protocol allows user to save on transaction fees.

The safety of our protocol is based on the fact that honest participants hold some transactions (the latest graft) that can be put on chain whenever needed in order to commit the latest state to the blockchain. The efficiency of our protocol follows from participants not having to put these transaction on chain until the very end of the contract (if all participants are honest).

This mechanism of floating transactions is reminiscent of the one exploited by the Lightning Network Protocol [8]. While this is a widely adopted and studied protocol, it only enables a limited subset of contracts (mainly focusing on micropayment channels). By contrast, our protocol can be applied to a generic contract tree. Other techniques to efficiently execute Bitcoin contracts rely on extending the Bitcoin protocol to add a new signature type [9]. Finally, some approaches trade off a more complex infrastructure in exchange more flexible smart contract: for instance [10] employs an external trusted execution environment to certify the contract execution, while [11] creates a new layer 2 blockchain that uses Bitcoin as part of its consensus protocol. By contrast, our protocol can be executed on stock Bitcoin without requiring any modification to the Bitcoin protocol, enlarging the trusted computing base, or overlaying a complex blockchain infrastructure.

References

[1] H. A. Kalodner, S. Goldfeder, X. Chen, S. M. Weinberg, E. W. Felten, Arbitrum: Scalable, private smart contracts, in: USENIX Security Symposium, 2018. URL: http://stevengoldfeder.com/papers/ Arbitrum-USENIX.pdf.

[2] C. Li, B. Palanisamy, R. Xu, Scalable and privacy-preserving design of on/off-chain smart contracts, in: 2019 IEEE 35th International Conference on Data Engineering Workshops (ICDEW), 2019, pp. 7–12. doi:10.1109/ICDEW.2019.00-43.

[3] A. De Salve, L. Franceschi, A. Lisi, P. Mori, L. Ricci, L2DART: A trust management system integrating blockchain and off-chain computation, ACM Trans. Internet Technol. 23 (2023). URL: https://doi.org/10.1145/3561386. doi:10.1145/3561386.

[4] M. Bartoletti, T. Cimoli, R. Zunino, Fun with Bitcoin smart contracts, in: ISoLA, 2018, pp. 432–449. doi:10.1007/978-3-030-03427-6\_32.

[5] M. Bartoletti, R. Zunino, BitML: a calculus for Bitcoin smart contracts, in: ACM CCS, 2018. doi:10.1145/3243734.3243795.

[6] N. Atzei, M. Bartoletti, T. Cimoli, S. Lande, R. Zunino, SoK: unraveling Bitcoin smart contracts, in: POST, volume 10804 of LNCS, Springer, 2018, pp. 217–242. doi:10.1007/978-3-319-89722-6.

[7] M. Andrychowicz, S. Dziembowski, D. Malinowski, L. Mazurek, Secure multiparty computations on Bitcoin, in: IEEE S & P, 2014, pp. 443–458. doi:10.1109/SP.2014.35, first appeared on Cryptology ePrint Archive, http://eprint.iacr.org/2013/784.

[8] J. Poon, T. Dryja, The Bitcoin Lightning Network: Scalable off-chain instant payments, 2015. URL: https://lightning.network/lightning-network-paper.pdf.

[9] C. Decker, R. Russell, eltoo : A simple layer 2 protocol for Bitcoin, 2018. URL: http://diyhpl.us/ ~bryan/papers2/bitcoin/eltoo.pdf.

[10] P. Das, L. Eckey, T. Frassetto, D. Gens, K. Hostáková, P. Jauernig, S. Faust, A.-R. Sadeghi, FASTKITTEN: practical smart contracts on bitcoin, in: Proceedings of the 28th USENIX Conference on Security Symposium, SEC’19, USENIX Association, USA, 2019, p. 801–818.

[11] sBTC working group, Stacks: a Bitcoin Layer for Smart Contracts, 2023. URL: https://stx.is/ nakamoto.