CCN: Decentralized Cross-Chain Channel Networks Supporting Secure and Privacy-Preserving Multi-Hop Interactions

TL;DR

The paper tackles the challenge of secure and privacy-preserving multi-hop cross-chain interactions, focusing on active and passive offline failures and unlinkability. It introduces CCN, a decentralized network that uses R-HTLC with an hourglass mechanism and a multi-path refund strategy, underpinned by zk-SNARKs to generate independent hash locks and preserve unlinkability. The scheme achieves cross-chain atomicity and unlinkability while enabling variable fund amounts, and it is validated through a multi-chain implementation on Ethereum and Cosmos. Experimental results demonstrate offline-issue resilience and practical overheads, highlighting CCN's potential for scalable, privacy-preserving cross-chain interoperability across heterogeneous blockchains.

Abstract

Cross-chain technology enables interoperability among otherwise isolated blockchains, supporting interactions across heterogeneous networks. Similar to how multi-hop communication became fundamental in the evolution of the Internet, the demand for multi-hop cross-chain interactions is gaining increasing attention. However, this growing demand introduces new security and privacy challenges. On the security side, multi-hop interactions depend on the availability of multiple participating nodes. If any node becomes temporarily offline during execution, the protocol may fail to complete correctly, leading to settlement failure or fund loss. On the privacy side, the need for on-chain transparency to validate intermediate states may unintentionally leak linkable information, compromising the unlinkability of user interactions. In this paper, we propose the Cross-Chain Channel Network (CCN), a decentralized network designed to support secure and privacy-preserving multi-hop cross-chain transactions. Through experimental evaluation, we identify two critical types of offline failures, referred to as active and passive offline cases, which have not been adequately addressed by existing solutions. To mitigate these issues, we introduce R-HTLC, a core protocol within CCN. R-HTLC incorporates an hourglass mechanism and a multi-path refund strategy to ensure settlement correctness even when some nodes go offline during execution. Importantly, CCN addresses not only the correctness under offline conditions but also maintains unlinkability in such adversarial settings. To overcome this, CCN leverages zero-knowledge proofs and off-chain coordination, ensuring that interaction relationships remain indistinguishable even when certain nodes are temporarily offline.

Figures (8)

• Figure 1: Simulation of active offline issue (a) and passive offline issue (b).
• Figure 2: This illustration provides an overview of the cross-chain channel network $\mathsf{CCN}$. The orange arrows represent off-chain channels, and cross-chain settlement between different blockchains is facilitated via $\mathsf{R\text{-}HTLC}$.
• Figure 3: The logic diagram of the circuits in $\mathsf{R\text{-}HTLC.Prepare}$ -- the circuit on the left is denoted as $\Lambda^{\mathsf{Pre.}}_{CA}$, while the one on the right is denoted as $\Lambda^{\mathsf{Pre.}}_{CB}$.
• Figure 4: The logic diagram of the circuits in $\mathsf{R\text{-}HTLC.Unlock}$ -- the circuit on the left is denoted as $\Lambda^{\mathsf{Unl.}}_{C\xi}$, while the one on the right is denoted as $\Lambda^{\mathsf{Unl.}}_{B\xi}$.
• Figure 5: An example of a multi-hop cross-chain transfer. The orange arrows represent the off-chain channels and the on-chain receipts are unlinkable.

Theorems & Definitions (11)

• Definition 1: Security Against Offline Issues
• Definition 2: Unlinkability Game
• Definition 3: Cross-Chain Atomicity
• Definition 4: HTLC in Cross-chain Scenarios
• Definition 5: Off-chain Channel
• Definition 6: zk-SNARK
• Definition 7
• Theorem 1: Atomicity
• proof : Proof Sketch
• Theorem 2: Unlinkability