ERC-721 Delatage Registry

Note: This contract has not been audited.

Summary

This contract is a minimally simple registry that allows NFT owners to be able to delegate their ERC-721 tokens without having to hand over full control of their assets. A delegate is an address that is able to enact some functionality that has been built on top of this contract without having the ability to transfer the delegated NFT.

• A delegate can sign data off-chain or submit a transaction on-chain to prove ownership by proxy without being able to transfer the NFT
• Only the current NFT owner can set the delegate address
• There can only be one delegate at a time for an NFT

Potential Use Cases

• Proving Ownership of Custodial NFTs
• NFT Renting
• Event Check In

Proving Ownership of Custodial NFTs

As the value of NFTs increases over time, owners will seek out solutions to help custody their expensive NFTs. However, now that their assets are being held by a custodian it makes it difficult for external parties to verify who owns what. You are no longer able to sign an off-chain message proving you own an asset if it is being held in a custodial address.

Problem:

Your rare NFT is now worth over 100 ETH and you don't feel comfortable with self custody. You then pay a third-party to custody the asset for you. A few days later you learn that there will be an airdropped NFT to all holders. As a result, you are unable to claim your airdropped asset in time since the necessary NFT is being held by a custodial service.

Solution:

You register a different address as a delegate and then pass the NFT off to the custodian. Now anytime they need to prove ownership of an NFT that is in custody; the service, smart contract, or middleware that is validating ownership checks if the off-chain signature or on-chain transaction came from a delegate address and allows them to claim the airdropped NFT.

NFT Renting

As the utility of NFTs increases over time, certain owners will want to rent out their assets. However, renting out an NFT could be dangerous because if you transfer the NFT to the renter then you are trusting them not to sell it at a profit since the market price will be higher than the rental price. Therefore, it is necessary to be able to create an air gap between the renter being able to access the utility of an NFT and the ability to transfer the NFT.

Problem:

You own a game NFT that represents a plot of land with valuable mineral deposits. You strike up a deal to rent out the mining rights for 10 ETH per month. You get your 10 ETH upfront and then transfer the NFT to the renter so that they can start mining. However, because the land is worth 1000 ETH they immediately sell it, make a profit, and run off with the money.

Solution:

An NFT rental service is built on top of this contract and registers the renter's address as a delegate when the agreement starts. The game's NFT validation software checks if the off-chain signature or on-chain transaction came from a valid delegate address. If it does come from a valid address it allows the renter to start extracting resources. In this scenario, the renter was able to access the utility of the land, but was never given access to transfer the NFT.

Event Check In

Token gated events are growing in popularity. These events sometimes require that an owner signs a message to prove that they own the correct NFT to get in. However, the user needs to have their expensive NFTs in a mobile wallet when they go to the event. This creates unnecessary risk and might not be possible if the NFT is being held by a custodian.

Problem:

You are going to large event in a major city. The event requires that you have your 100 ETH NFT on your phone to sign a message. Transferring your valuable NFT to a mobile device and then walking around in a major city is less than ideal from a safety standpoint.

Solution:

You register an empty address in your mobile wallet as a delegate. When you arrive you can produce a signature from the empty mobile wallet and the event can check if that address is a delegate. This method is safer since you would no longer need to carry around expensive NFTs to gain access to their utility.

Contract Interface

getDelegate

Returns the delegate address for a given ERC-721 NFT.

function getDelegate(address _tokenAddress, uint _tokenId)

setDelegate

Sets the delegate address for a given ERC-721 NFT.

function setDelegate(
    address _tokenAddress,
    uint _tokenId,
    address _delegateAddress
)

setDelegateWithSig

Sets the delegate address for a given ERC-721 NFT with a signature from the owner.

function setDelegateWithSig(
    address _tokenAddress,
    uint _tokenId,
    address _delegateAddress,
    bytes memory _signature
)

DelegateSet Event

Emitted whenever a new delegate address is set.

event DelegateSet(address tokenAddress, uint tokenId, address owner, address delegateAddress);