Paper 2023/1909

Ratel: MPC-extensions for Smart Contracts

Yunqi Li, University of Illinois at Urbana-Champaign
Kyle Soska, University of Illinois at Urbana-Champaign
Zhen Huang, Shanghai Jiao Tong University
Sylvain Bellemare, The Initiative for CryptoCurrencies and Contracts
Mikerah Quintyne-Collins, HashCloak Inc.
Lun Wang, UC Berkeley
Xiaoyuan Liu, UC Berkeley
Dawn Song, UC Berkeley
Andrew Miller, University of Illinois at Urbana-Champaign

Enhancing privacy on smart contract-enabled blockchains has garnered much attention in recent research. Zero-knowledge proofs (ZKPs) is one of the most popular approaches, however, they fail to provide full expressiveness and fine-grained privacy. To illustrate this, we underscore an underexplored type of Miner Extractable Value (MEV), called Residual Bids Extractable Value (RBEV). Residual bids highlight the vulnerability where unfulfilled bids inadvertently reveal traders’ unmet demands and prospective trading strategies, thus exposing them to exploitation. ZKP-based approaches failed to ad- dress RBEV as they cannot provide post-execution privacy without some level of information disclosure. Other MEV mitigations like fair-ordering protocols also failed to address RBEV. We introduce Ratel, an innovative framework bridging a multi-party computation (MPC) prototyping framework (MP-SPDZ) and a smart contract language (Solidity), harmonizing the privacy with full expressiveness of MPC with Solidity ’s on-chain programmability. This synergy empowers developers to effortlessly craft privacy-preserving decentralized applications (DApps). We demonstrate Ratel’s efficacy through two distinguished decentralized finance (DeFi) applications: a decentralized exchange and a collateral auction, effectively mitigating the potential RBEV issue. Furthermore, Ratel is equipped with a lightweight crash-reset mechanism, enabling the seamless recovery of transiently benign faulty nodes. To prevent the crash-reset mechanism abused by malicious entities and ward off DoS attacks, we incorporate a cost-utility analysis anchored in the Bayesian approach. Our performance evaluation of the applications developed under the Ratel framework underscores their competency in managing real-world peak-time workloads.

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yunqil3 @ illinois edu
soska @ ramiel capital
xmhuangzhen @ gmail com
sbellem @ gmail com
mikerah @ hashcloak com
wanglun @ berkeley edu
xiaoyuanliu @ berkeley edu
dawnsong @ gmail com
soc1024 @ illinois edu
2024-05-08: revised
2023-12-12: received
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      author = {Yunqi Li and Kyle Soska and Zhen Huang and Sylvain Bellemare and Mikerah Quintyne-Collins and Lun Wang and Xiaoyuan Liu and Dawn Song and Andrew Miller},
      title = {Ratel: {MPC}-extensions for Smart Contracts},
      howpublished = {Cryptology ePrint Archive, Paper 2023/1909},
      year = {2023},
      note = {\url{}},
      url = {}
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