Harmonia: Securing Cross-Chain Applications Using Zero-Knowledge Proofs

Abstract

The field of blockchain interoperability plays a pivotal role in blockchain adoption. Despite these advances, a notorious problem persists: the high number and success rate of attacks on blockchain bridges. We propose Harmonia, a framework for building robust, secure, efficient, and decentralized cross-chain applications. A main component of Harmonia is DendrETH, a decentralized and efficient zero-knowledge proof-based light client. DendrETH mitigates security problems by lowering the attack surface by relying on the properties of zero-knowledge proofs. The DendrETH instance of this paper is an improvement of Ethereum’s light client sync protocol that fixes critical security flaws. This light client protocol is implemented as a smart contract, allowing blockchains to read the state of the source blockchain in a trust-minimized way. Harmonia and DendrETH support several cross-chain use cases, such as secure cross-blockchain bridges (asset transfers) and smart contract migrations (data transfers), without a trusted operator. We implemented Harmonia in 9K lines of code. Our implementation is compatible with the Ethereum Virtual Machine (EVM) based chains and some non-EVM chains. Our experimental evaluation shows that Harmonia can generate light client updates with reasonable latency, costs (a dozen to a few thousand US dollars per year), and minimal storage requirements (around 4.5 MB per year). We also carried out experiments to evaluate the security of DendrETH. We provide an open-source implementation and reproducible environment for researchers and practitioners to replicate our results.

Leveraging Zero-Knowledge Proofs for Blockchain Interoperability: Experiences with Ethereum and Hyperledger Fabric

“…The authors used zkp to prove (in Ethereum) the existence of a block committed in Cosmos, and we used them to prove the existence of permissioned data in Fabric. However, the authors' costs analysis showed that block validation can cost 0.3 dollars, which gives 2136,6 dollars per day 5 . These results are aligned with our results as zkp are yet expensive to be used in real-world scenarios.…”

“…Belchior et al [5] proposed Harmonia, a framework to build cross-chain applications. One of its components is DendrETH, a decentralised zero-knowledge proof-based light client that prevents the Ghost Checkpoint Attestation Attack.…”

“…Furthermore, our work involves permissioned and permissionless blockchains, rather than only permissionless blockchains. 5 As the 30th march Ethereum generates 7122 blocks per day Overall, most related work is focused on the design of light clients, and one work is related to anonymous crosschain authentication. Our work complements the existing body of knowledge by proposing a new cross-chain authentication scheme between Ethereum and Fabric that shares design similarities with the existing work, but considers the specifics of these two blockchains.…”