PBT (Physical Backed Token)

NFT collectors enjoy collecting digital assets and sharing them with others online. However, there is currently no such standard for showcasing physical assets as NFTs with verified authenticity and ownership. Existing solutions are fragmented and tend to be susceptible to at least one of the following:

• The NFT cannot proxy as ownership of the physical item. In most current implementations, the NFT and physical item are functionally two decoupled distinct assets after the NFT mint, in which the NFT can be freely traded independently from the physical item.

• Verification of authenticity of the physical item requires action from a trusted entity (e.g. StockX).

PBT aims to mitigate these issues in a decentralized way through a new token standard (an extension of EIP-721).

From the Azuki team. Chiru Labs is not liable for any outcomes as a result of using PBT, DYOR. Repo still in beta.

Resources

• pbt.io
• Draft EIP
• Blog

How does it work?

Requirements

This approach assumes that the physical item must have a chip attached to it that fulfills the following requirements (Kong is one such vendor for these chips):

• The ability to securely generate and store an ECDSA secp256k1 asymmetric keypair
• The ability to sign messages from the private key of the asymmetric keypair
• The ability for one to retrieve only the public key of the asymmetric keypair (private key non-extractable)

The approach also requires that the contract uses an account-bound implementation of EIP-721 (where all EIP-721 functions that transfer must throw, e.g. the "read only NFT registry" implementation referenced in EIP-721). This ensures that ownership of the physical item is required to initiate transfers and manage ownership of the NFT, through a new function introduced in IPBT.sol (transferTokenWithChip).

Approach

On a high level:

• Each NFT is conceptually linked to a physical chip.
• The NFT can only be transferred to a different owner if a signature from the chip is supplied to the contract.
• This guarantees that a token cannot be transferred without consent from the owner of the physical item.

More details available in the EIP and inlined into IPBT.sol.

Reference Implementation

A simple mint for a physical drop could look something like this:

import "@openzeppelin/contracts/access/Ownable.sol";
import "@chiru-labs/pbt/src/PBTSimple.sol";

contract Example is PBTSimple, Ownable {

    /// @notice Initialize a mapping from chipAddress to tokenId.
    /// @param chipAddresses The addresses derived from the public keys of the chips
    constructor(address[] memory chipAddresses, uint256[] memory tokenIds)
        PBTSimple("Example", "EXAMPLE")
    {
        _seedChipToTokenMapping(chipAddresses, tokenIds);
    }

    /// @param signatureFromChip The signature is an EIP-191 signature of (msgSender, blockhash),
    ///        where blockhash is the block hash for a recent block (blockNumberUsedInSig).
    /// @dev We will soon release a client-side library that helps with signature generation.
    function mintPBT(
        bytes calldata signatureFromChip,
        uint256 blockNumberUsedInSig
    ) external {
        _mintTokenWithChip(signatureFromChip, blockNumberUsedInSig);
    }
}

As mentioned above, this repo is still in beta and more documentation is on its way. Feel free to contact @2pmflow if you have any questions.

Contributing

Contributions are what make the open source community such an amazing place to learn, inspire, and create. Any contributions you make are greatly appreciated.

1. Fork the project
2. Create your feature branch (git checkout -b feature/AmazingFeature)
3. Commit your changes (git commit -m 'Add some AmazingFeature')
4. Push to the branch (git push origin feature/AmazingFeature)
5. Open a pull request

License

Distributed under the MIT License.