Front-running attacks, which benefit from advanced knowledge of pending transactions, have proliferated in the blockchain space since the emergence of decentralized finance. Front-running causes devastating losses to honest participants and continues to endanger the fairness of the ecosystem. We present Flash Freezing Flash Boys (F3B), a blockchain architecture that addresses front-running attacks by using threshold cryptography. In F3B, a user generates a symmetric key to encrypt their transaction, and once the underlying consensus layer has finalized the transaction, a decentralized secret-management committee reveals this key. F3B mitigates front-running attacks because, before the consensus group finalizes it, an adversary can no longer read the content of a transaction, thus preventing the adversary from benefiting from advanced knowledge of pending transactions. Unlike other mitigation systems, F3B properly ensures that all unfinalized transactions, even with significant delays, remain private by adopting per-transaction protection. Furthermore, F3B addresses front-running at the execution layer; thus, our solution is agnostic to the underlying consensus algorithm and compatible with existing smart contracts. We evaluated F3B on Ethereum with a modified execution layer and found only a negligible (0.026%) increase in transaction latency, specifically due to running threshold decryption with a 128-member secret-management committee after a transaction is finalized; this indicates that F3B is both practical and low-cost.

翻译：前置交易攻击利用对未决交易的预知优势谋利，自去中心化金融兴起以来在区块链领域泛滥。该攻击导致诚实参与者遭受毁灭性损失，持续威胁生态系统的公平性。我们提出Flash Freezing Flash Boys（F3B）架构，采用门限密码学抵御前置交易攻击。在F3B中，用户生成对称密钥加密交易，待底层共识层最终确定交易后，去中心化密钥管理委员会再公开该密钥。由于攻击者在共识组最终确定交易前无法读取交易内容，因而无法从对未决交易的预知中获利，F3B有效缓解了前置交易攻击。与其他防御系统不同，F3B通过采用逐笔交易保护机制，确保所有未最终确定的交易——即使存在显著延迟——始终保持隐私。此外，F3B在执行层应对前置交易攻击，因此本方案与底层共识算法无关，且兼容现有智能合约。我们在以太坊上通过修改执行层对F3B进行评测，发现在交易最终确定后，由128成员密钥管理委员会执行门限解密操作仅导致交易延迟出现可忽略的0.026%增长——这表明F3B兼具实用性与低成本特性。