Towards Secure and Efficient Route Computation for Cross-Chain Message Delivery

Abstract

Demand for blockchain applications has led to a surge of new public blockchains. However, this fragments liquidity and pushes users to bridge across unfamiliar protocols, increasing risk and complexity. Cross-chain communication enables interoperability, allowing contracts to execute logic and move assets across chains. Yet current delivery solutions either support message passing only between directly connected chains, limiting connectivity, or are centralized and route through a single hub chain that introduces a single point of failure and requires trust in the hub operator.

Inter-blockchain communication can become more robust by leveraging concepts from traditional network architectures, including routing, name resolution, and policy-based message delivery. These mechanisms can increase connectivity by enabling chains that are not directly connected to communicate securely over multi-hop routes.

This thesis studies the problem of policy-driven cross‑chain routing: Current cross-chain routing is largely ad-hoc and manual, and does not reliably respect users' security or cost preferences when no direct connection exists. Given a dynamic inter‑chain topology and user policies (e.g., security thresholds, fee budgets, latency targets), we compute routes over multi‑hop Inter-Blockchain Communication (IBC) while ensuring (a) security constraints are strictly enforced on-chain and (b) preference constraints (e.g., minimizing gas costs) are met with practical guarantees. This is challenging because the required inputs (e.g., fees, validator sets, congestion, and application-specific state) change independently on each chain, yet the resulting route and its policy compliance must be verifiable on the destination chain at a reasonable cost. We present a modular stack: a Transport Layer with Policy Enforcement Module, a Relayer Control Plane for route computation, and a Relayer Data Plane for execution, which separates concerns between policy specification, route computation, and delivery.

We introduce three routing methods: (1) Single‑Relayer routing, which computes routes off‑chain independently by off-chain relayer nodes, (2) zkRouter, which computes routes off‑chain with a succinct zero‑knowledge proof of policy compliance and (3) Relayer Network, a new collaborative overlay that distributes operational load (client updates, packet relaying) across relayers. Our prototypes demonstrate that our stack is practical and achieves higher decentralization, better connectivity, and greater scalability, enabling richer and safer cross-chain applications while preserving IBC’s security assumptions and without significant fee overhead. Our evaluation shows: (1) near 90% connectivity vs. 15% for hub-and-spoke; (2) more than 30% connectivity after removing top four chains, reaching 50% with topology upgrades; (3) less than $0.10 on-chain cost per message; (4) scales to more than 10^6 messages maintaining low processing time.