Launching Harmony — Binance Smart Chain Bridge

The Harmony and Binance Smart Chain bridge is now live at

Sahil Dewan
Mar 22 · 4 min read

In November 2020, Harmony community launched the Horizon bridge that connects Ethereum and Harmony blockchains. Users have been able to bridge their Ethereum assets (ETH, ERC20, ERC721) over to Harmony. Now we are adding support for bridging BNB and BEP20 assets over to Harmony.

The Binance Smart Chain bridge will open the gates for the Binance Smart Chain assets and applications to freely interact with the Harmony blockchain and its growing application ecosystem.

Why bridging with multiple blockchains?

DeFi protocols and NFT marketplaces are already being launched by the community. The Horizon Bridge connects Harmony with Ethereum and Binance Smart Chain, and later will add support for Polkadot, Bitcoin and Cosmos.

These developments will not only enable existing Ethereum applications to scale, but also speed up innovation around multi-chain applications, such as multi-chain, non-custodial decentralized exchanges.

Technical Overview

The Binance Smart Chain bridge has a similar architecture to the Ethereum bridge. It follows the same lock and mint, and burn and unlock asset flows whenever an asset transfers over the bridge. The smart contracts are a replica of the prior Ethereum bridge contracts which have been audited by PeckShield. To get an in-depth overview, you can revisit the bridge architecture in this post.

While the contracts of the Binance Smart Chain and Ethereum bridges are separate, you can access both the bridges using the same front-end and connect your same metamask account to migrate assets across multiple networks.

An important thing to note is that the bridge treats each asset coming from a different chain uniquely.

For example, Alice wants to bridge over 10 USDT (ERC20) from Ethereum. Whereas Bob wants to bridge over 5 USDT (BEP20) from Binance Smart Chain.

In the bridge design, 10 USDT (Ethereum) and 5 USDT (Binance Smart Chain) will be minted by separate contracts. As a result, the bridge will give 10 ethUSDT (HRC20) to Alice and 5 bscUSDT (HRC20) to Bob. These USDT tokens will be treated as two different assets by the bridge.

For now, a user will not be able to bridge USDT (and similar assets that exist on both chains) from Ethereum directly to Binance Smart Chain. Soon, decentralized exchanges on Harmony will make this flow easy for users by introducing liquidity pools between ethUSDT-bscUSDT.

An alternative design choice was for the bridge to aggregate liquidity for the same asset coming from different chains. Which means, in our above example, the bridge would mint the same USDT (HRC20) asset on Harmony whether the USDT was coming from Ethereum or Binance Smart Chain.We explored various security and trust assumptions for both these design choices.

We recommended solving for the liquidity aggregation at the application layer, instead of the bridge layer.

The bridge should have a simple, lightweight and trustless architecture. Various applications like a decentralized exchange (AMM) can introduce new contracts for pooling or aggregating liquidity of the same but multi-chain asset. We invite proposals from our developer community to solve these new horizon issues as we enter the multi-chain world.

Get started with the Binance Smart Chain Bridge by following this step-by-step guide!

View all the Bridged Assets under the ‘Assets’ tab

View the status of Bridge transactions under the ‘Transactions’ tab

Note: At launch, you can bridge any BEP20 assets from Binance Smart Chain to Harmony. Support for migrating native BNB to Harmony, and for migrating native ONE to Binance Smart Chain will be launched by end of this week.


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