Multichain NFT

This project is a submition to ETHGlobal Waterloo 2023 hackaton. Project page

Multichain NFTs have all of the properties of regular NFTs, but can exist on many chains at the same time. NFTs are often used as a proof of something. Many protocols are working on different chains at the same time, yet users, who bought the NFT, can access services only on one chain, because of challenges blockchain interoperability possesses.

Protocol

A ERC721Multichain contract is fully compatible with regular ERC721, but adds several new functions on top.

1. ERC721Multichain can wrap other NFTs. Basically, you send your precious NFT to this contract, and receive an NFT that serves as proof of deposit. Token can be easily wrapped & unwrapped at any time, as long as you have this proof of deposit NFT.
2. Having an ERC721Multichain, you can mint ERC721Multichain on other chains just with a call of a function on source chain.
3. ERC721Multichain on all chains share the same tokenId. Even better, tokenId is fully deterministic, and is calculated as

uint256(keccak256(abi.encode(originalNftContract, originalNftTokenId)))

4. Every token has its main chain - where the original NFT is locked. Token metadata is accessible only through main chain.
5. When a token is transferred on one chain, it is guaranteed to be transferred on all other chains as well.
6. When a token is approved on one chain, spender will be able to transfer token on all chains at the same time.
7. In order to unwrap token, it needs to be burned on all other chains.
8. Token on main chain keeps track of all tokens on other chains. Adding new chains can only be done through the main chain.

Overview of additional functions

// Perform transfer on all chains at the same time
function multichainTransferFrom(
    address from,
    address to,
    uint256 tokenId
) public payable;

// Mint a token on another chain
function bridgeToken(uint32 destination, uint256 tokenId) public payable;

// Burn a token on a non-main chain
// On main chain unwrap() has to be used
function burn(uint256 tokenId) external payable;

function wrap(address originalToken, uint256 originalTokenId) external;
function unwrap(uint256 tokenId) external;

Bridge contract

A huge role in interchain communication serves Bridge contract. From the point of view of ERC721Multichain contract, it sends message to Bridge contract, and receives this message on destination chain from Bridge contract.

Interchain communication

Bridge contract uses Hyperlane protocol to send and receive interchain messages.

Terminology

• Transfer. In case token exists only on one chain, a regular transferFrom will be performed. In case token exists on many chains, a multichainTransferFrom will be called.
• Mint. Create the token on a new chain.
• Burn. Remove the token from a chain. A token can't be removed from main chain.
• Wrap. Lock an NFT to receive a fancier Multichain NFT
• Unwrap. Give up your Multichain NFT, get back your regular NFT.

Frontend client

In frontend client you can see any