Rollup protocols have recently received significant attention as a promising class of Layer 2 (L2) scalability solutions. By utilizing the Layer 1 (L1) blockchain solely as a bulletin board for a summary of the executed transactions and state changes, rollups enable secure off-chain execution while avoiding the complexity of other L2 mechanisms. However, to ensure data availability, current rollup protocols require the plaintext of executed transactions to be published on-chain, resulting in inherent privacy limitations. In this paper, we address this problem by introducing Calyx, the first privacy-preserving multi-token optimistic-Rollup protocol. Calyx guarantees full payment privacy for all L2 transactions, revealing no information about the sender, recipient, transferred amount, or token type. The protocol further supports atomic execution of multiple multi-token transactions and introduces a transaction fee scheme to enable broader application scenarios while ensuring the sustainable operation of the protocol. To enforce correctness, Calyx adopts an efficient one-step fraud-proof mechanism. We analyze the security and privacy guarantees of the protocol and provide an implementation and evaluation. Our results show that executing a single transaction costs approximately $0.06 (0.00002 ETH) and incurs only constant-size on-chain cost in asymptotic terms.

翻译：汇总协议作为一类前景广阔的Layer 2（L2）扩容方案，近期受到广泛关注。此类协议仅将Layer 1（L1）区块链作为记录交易摘要与状态变更的公告板，在实现安全链下执行的同时，避免了其他L2机制的复杂性。然而，为确保数据可用性，现有汇总协议需将已执行交易的明文发布至链上，这导致了固有的隐私限制。本文通过提出首个支持隐私保护的多代币乐观汇总协议Calyx来解决该问题。Calyx为所有L2交易提供完整的支付隐私保护，确保发送方、接收方、转账金额及代币类型等信息的零泄露。该协议进一步支持多笔多代币交易的原子化执行，并引入交易费用机制以拓展应用场景，同时保障协议可持续运行。为验证执行正确性，Calyx采用高效的单步欺诈证明机制。我们分析了协议的安全性与隐私保障特性，并提供了具体实现与性能评估。实验结果表明，单笔交易执行成本约为0.06美元（0.00002 ETH），且其链上开销在渐进意义上仅为常量级。