Harmony’s Horizon bridge was one of the first cross-chain bridges that launched back in October 2020, which has since accrued a peak Total Volume Locked (TVL) of ~$750 million with over $1.5 billion transaction volume across 100k+ cross-chain transactions.
The Horizon bridge stood the test of time for two years before an exploit happened on June 23, 2022, that resulted in the loss of $100 million in assets. While this exploit was a huge setback, Harmony strongly believes in the cross-chain future and will continue to support the refinement of the cross-chain technology by deploying products and innovating. While the pause of the Horizon bridge was not ideal for our users, these four months were needed to work on the reimbursement strategies with the community and to find the right partner to relaunch the Horizon bridge.
The cross-chain technology space is rapidly evolving with many successful solutions. This article describes our exploration, classification, and findings that went into selecting a bridging partner for resuming Horizon. We carefully considered bridging solutions like Nomad, Celer, Axeler, Synapse, Multichain and LayerZero. All these solutions seem to be strong and have demonstrated a considerable amount of user adoption. After thorough technical due diligence, we have opted for LayerZero as our bridging partner for resuming Horizon, and we highlight some of our reasoning behind our choice.
“When evaluating our choices for a bridge partner, LayerZero stood out in terms of technical strength, security, and support from top-tier VCs and ecosystem developers. We believe they are the right partner for Harmony as we resume Horizon bridge.” said Stephen Tse, Founder of Harmony.
LayerZero is an omnichain interoperability protocol specifically designed for lightweight message passing across blockchains. LayerZero’s stargate.finance deployment was the fastest growing DeFi protocol reaching $4.4B TVL in 2 weeks post-launch; today it has accrued over $500 million TVL across 7 blockchains such as Ethereum, BSC, Avalanche, Polygon, Arbitrum, Optimism, and Fantom. LayerZero is currently live on 16 mainnets and many more testnets.
LayerZero Labs is a dedicated team of builders who are constantly innovating and specializing in cross-chain technologies. As seen in our classification, LayerZero is a committee-based bridging solution whose security relies upon the oracle network which is a custom deployment of Chainlink’s Decentralized Oracle Network (DON) with well-backed operators like FTX, Polygon, and Sequoia. The main job of the oracle network is to validate and accept the cross-chain block headers such that users’ cross-chain transaction proofs can be validated. Another key infrastructure is the transaction proof generator and relayer, which is currently run by LayerZero itself. The relayer can be run by any party as long as it is not run by the oracle providers, to ensure bridge’s security.
In the context of Horizon, we have replaced the previously existing multisig validation layer with LayerZero’s validation layer. This greatly reduces risk, as Harmony does not need to run/maintain any backend infrastructure, as the two key pieces of infrastructure that comprise the LayerZero validation (the oracle and the relayer) are professionally run and maintained by the third-party operators with expertise.
“We’re excited to partner w/ Harmony to bring the best of LayerZero to their ecosystem and enable resumption of Harmony’s Horizon bridge and enable cross-chain applications,” said Bryan Pellegrino, CEO of LayerZero.
Further, we have taken additional security steps to proactively monitor and prevent future hacks by partnering with Lossless, who will deploy their latest innovation Aegis, a proactive web3 security infrastructure. Lossless Aegis framework will continuously monitor the Horizon bridge to detect any suspicious activities and prevent future attacks on the bridge.
Lossless Aegis provides industry-leading threat monitoring and smart contract defense capabilities, designed to prevent exploits before they happen. Lossless Aegis scans all mined block transactions, utilizing predictive analytics to identify transaction patterns and suspicious addresses. Data on potentially malicious behavior is then pushed both on-chain and off-chain, triggering real-time user alerts. Evidence of the Lossless team’s competence can be seen in their efforts to prevent the exploiter of the Horizon bridge from stealing the AAG token liquidity, where the Lossless team was able to recover 78 million worth of AAG tokens.
From the user perspective, using Horizon bridge will be similar to before but with a better user experience, as we have deployed a new frontend for Horizon. The bridge users will not experience any major changes with respect to use; however, the cost and the delay involved in using the bridge have been greatly reduced due to the removal of the on-chain multisig operational cost. The diagram below demonstrates the bridging flow from Ethereum to Harmony.
In terms of the assets, de-pegged tokens no longer will be supported in the Horizon bridge, and they will be replaced with the new wrapped assets. At the time of the relaunch, the following will be supported:
Ethereum side –
stablecoins such as USDC, USDT, DAI, BUSD, FRAX can be bridged. Other assets like ETH, WBTC, AAG, FXS, (x)SUSHI, and AAVE are also supported.
On the Binance Smart Chain side, BNB, BUSD are initially supported. The native ONE token can also be bridged over to both Ethereum and BSC like before.
Unlike before, however, adding support for new or previously existing assets is not permissionless, and it will require additional deployment efforts by the Harmony bridge team. Based on demand and partner requests, we plan to gradually add support for more assets to the bridge over time.
The Horizon bridge exploit was an extremely difficult incident, but we will emerge stronger as ONE. We look forward to building back trust and strengthening our cross-chain ecosystem, with the support of our beloved community by our side.
About Harmony
Harmony is an open and fast blockchain. Our mainnet runs Ethereum applications with 2-second transaction finality and 100 times lower fees.
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