The Fast Rainbow Bridge for NEAR to Ethereum Token Transfers is Live!

We are excited to announce the launch of the Fast Rainbow Bridge, a new option for transferring tokens from the NEAR blockchain to Ethereum in a matter of minutes. Unlike the classical Rainbow Bridge, which can take several hours, the Fast Bridge offers significantly faster token transfers while mitigating certain limitations of the traditional approach. After having been available in White List mode, the Fast Bridge is now available to all!

Let’s take a closer look at the changes introduced by the Fast Bridge and what users can expect.

Classical vs Fast Rainbow Bridge

With the Classical Rainbow Bridge, time required to bridge ERC-20 tokens from the NEAR and Aurora ecosystem to Ethereum takes between 4 and 8 hours. This is because the Classical Rainbow Bridge implements the following design:

Optimistic Approach: The classical Rainbow Bridge uses light-clients as its operational media, and for NEAR light client on Ethereum it uses an optimistic approach, whereby NEAR validators signatures are not checked by default, due to extremely high gas usage required for its verification on Ethereum. Only when challenged, the signatures are verified on-chain, leading to a 4-hour challenge period.

Frequency of NEAR Blocks Transfer: NEAR blocks' headers are sent to Ethereum only once every 4 hours due to the expensive gas fees on the Ethereum network. This can result in a total transfer time of up to 8 hours, including the block transfer and a challenge period.

Two-Phase Transfer: In the classical Rainbow Bridge, token transfers require two actions: initiating the transfer on the NEAR side and withdrawing the tokens on the Ethereum side. There can be a gap of up to 4 hours between these two actions, prolonging the overall transfer process. This approach requires the user to finalize the transfer on the Ethereum side by providing proof of the transfer, hence the finalization might be pretty expensive due to gas usage.

No Cancellation: Once a transfer is initialized, it cannot be canceled. The user must complete the transaction on the Ethereum side to retrieve the locked tokens. This process can take approximately 4 to 8 hours, plus an additional 20 minutes to receive the funds back on the NEAR side.

In order to enable fast transfers and overcome the limitations of the Classical Rainbow Bridge, the team introduced the three additional components:

LP-Relayer (Liquidity provider relayer): An off-chain service with accounts on both Ethereum and NEAR, the relayer holds liquidity in tokens on the Ethereum side and facilitates token transfers between NEAR and Ethereum. Upon receiving the tokens back on the NEAR side, the relayer transfers his funds back to Ethereum to replenish its liquidity using the classical Rainbow Bridge.

NearFastBridge: A contract on NEAR that locks tokens and transfers them to the relayer upon providing proof of the finalized transaction on the Ethereum side.

EthereumFastBridge: A contract on Ethereum used by the relayer to transfer tokens to users. This contract generates events of token transfers on the Ethereum side.

With the introduction of these new elements, the Rainbow Bridge is now able to perform transfers of ERC-20 tokens from the NEAR to the Ethereum ecosystem within a few minutes and with an additional relay fee.

The Fast Bridge solution is decentralized and trustless. This is achieved because the Fast Bridge allows multiple relayers to provide liquidity, thus allowing a competitive market for fast transfers. Users, on the other hand, may claim their tokens back if their transfer was not completed (for example, in case the relayer is down or the provided fee is too low) within the max transfer time window (currently equals to 4 hours). Moreover, to claim tokens back on the NEAR side, the relayer must provide proof of the finalized bridge transaction from the Ethereum side.

How Does it work?

During the token transfer from NEAR to Ethereum, the transaction flow follows these steps:

The User initiates the transfer by calling the init_transfer function in the NearFastBridge contract. This generates a unique nonce and emits the FastBridgeInitTransferEvent. The LP-Relayer captures the FastBridgeInitTransferEvent, checks if it satisfies the fee requirements, and transfers the tokens to the User on the Ethereum side using the transferTokens function in the EthereumFastBridge contract. The EthereumFastBridge contract then emits the TransferTokens event. The EthToNearRelayer submitsEthereum blocks to the Ethereum light client on the NEAR side. The LP_Relayer unlocks the tokens by calling the lp_unlock function in the NearFastBridge contract and provides the proof of the TransferTokens event. The NearFastBridge contract verifies the proof and transfers the tokens and fee to the LP-Relayer on the NEAR side.

What’s New for Users?

You can now choose to transfer ERC-20 tokens from the NEAR to the Ethereum ecosystem benefitting from the fast transfer function. With the valid fast transfer, you will be able to bridge your assets, usually in a few minutes. In the Fast Rainbow Bridge, the cost of the transfer is covered by the relayer, relieving the user from paying the gas fees on the Ethereum side. The relayer takes care of the gas expenses and ensures that the transaction is executed promptly to mitigate any potential gas price fluctuations.

The fee for utilizing the Fast Rainbow Bridge is calculated dynamically and paid in the same tokens that are transferred. The currentfee is equal to ~$20 base fee plus 0.1% of the transferred amount. From the start, the Fast Rainbow Bridge supports AURORA, WBTC, and USDC transfers, while new tokens will be added in the future. Currently, the Fast Rainbow Bridge requires a NEAR account to create the transfer, however our team is already working on adding the Fast Bridge option for the Aurora network. Stay tuned!

About Aurora

Aurora is a platform for Web3 developers to build pioneering and scalable distributed applications. Powered by its high-performance Ethereum Virtual Machine (the Aurora Engine) and fully trustless bridge (the Rainbow Bridge), Aurora combines the builder-friendly development experience of Ethereum with the modern blockchain performance of the NEAR Protocol to offer an environment for creating highly scalable, carbon-neutral, future-safe, and low-cost Web3 services.