Calyx: Privacy-Preserving Multi-Token Optimistic-Rollup Protocol

2025-09-30

AI Summary

Existing rollup protocols require publishing transaction data in plaintext on-chain to ensure data availability, leading to severe privacy leakage. This paper proposes Calyx—the first optimistic rollup protocol supporting full payment privacy across multiple tokens: it publishes only transaction digests on Layer 1, concealing sender, receiver, amount, and token type. We design atomic multi-transaction execution and a sustainable fee mechanism. Moreover, we introduce the first one-round fraud proof tailored for multi-token settings, integrating zero-knowledge encryption to guarantee correctness and availability. On-chain overhead is constant—per-transaction cost is merely $0.06 (0.00002 ETH). Experimental evaluation confirms Calyx’s efficiency, scalability, and practicality.

Technology Category

• Machine Learning: Privacy
• Multiagent Systems: Mechanism Design
• Natural Language Processing: Ethics — Bias, Fairness, Transparency & Privacy

Application Category

• Security and Privacy: Data transparency and provenance
• Responsible Web: Data and user privacy-enhancing technologies for the Web
• Economics, Online Markets and Human Computation: Fairness, privacy, and diversity in economic environments

Abstract

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.

Problem

• Ensuring transaction privacy in optimistic rollups by concealing sender, recipient, and amount
• Supporting atomic multi-token transactions with sustainable fee mechanisms
• Providing efficient fraud proofs while maintaining constant on-chain costs

Innovation

• Privacy-preserving optimistic rollup for multi-token transactions
• Efficient one-step fraud-proof mechanism for correctness
• Atomic execution of multiple multi-token transactions