zkBridge: Trustless Cross-chain Bridges Made Practical
Tiancheng Xie, Jiaheng Zhang, Zerui Cheng, Fan Zhang, Yupeng Zhang, Yongzheng Jia, Dan Boneh, and Dawn Song.
In ACM Conference on Computer and Communications Security (CCS), 2022.
Blockchains have seen growing traction with cryptocurrencies
reaching a market cap of over 1 trillion dollars, major institution
investors taking interests, and global impacts on governments, businesses, and individuals. Also growing significantly is the heterogeneity of the ecosystem where a variety of blockchains co-exist.
Cross-chain bridge is a necessary building block in this multi-chain
ecosystem. Existing solutions, however, either suffer from performance issues or rely on trust assumptions of committees that significantly lower the security. Recurring attacks against bridges have
cost users more than 1.5 billion USD. In this paper, we introduce
zkBridge, an efficient cross-chain bridge that guarantees strong
security without external trust assumptions. With succinct proofs,
zkBridge not only guarantees correctness, but also significantly
reduces on-chain verification cost. We propose novel succinct proof
protocols that are orders-of-magnitude faster than existing solutions for workload in zkBridge. With a modular design, zkBridge
enables a broad spectrum of use cases and capabilities, including
message passing, token transferring, and other computational logic
operating on state changes from different chains. To demonstrate
the practicality of zkBridge, we implemented a prototype bridge
from Cosmos to Ethereum, a particularly challenging direction that
involves large proof circuits that existing systems cannot efficiently
handle. Our evaluation shows that zkBridge achieves practical performance: proof generation takes less than 20 seconds, while verifying proofs on-chain costs less than 230K gas. For completeness,
we also implemented and evaluated the direction from Ethereum to
other EVM-compatible chains (such as BSC) which involves smaller
circuits and incurs much less overhead.