This repo is a sample implemtation of user-mintable, privacy-enabled NFTs showing the mint process using an on-chain anchor registry as backing for document verification.

The goals of a user-mintable, privacy-enabled NFT are

• Mint an NFT that represents an off-chain asset consisting of structured data
• Allow anyone to mint the NFT who can provide a proof that they should be allowed to mint this NFT
• Proofs are validate on-chain against an "anchor registry" that holds the merkle root hash of the off-chain document
• Thus turning off-chain assets into on-chain assets, represented as an ERC-721 token

The ERC-721 registry exposes a mint method that allows anyone to mint an NFT, provided they can supply a proof that they should be allowed to do so. Specifically, the registry allows minting NFTs for off-chain datasets/assets utilizing merkle proofs that are supplied to the mint method.

The mint method is called with plaintext fields and their corresponding proofs. The NFT registry checks the validity of the data & merkle proof against an on-chain anchor registry. The anchor registry contains a mapping of document identifier to the merkle root of the respective document (the off-chain asset). If the merkle proof that was supplied to the mint method validates correctly, the NFT registry mints the token that represents the off-chain asset.

The sample implementation utilizes the precise-proofs library to generate merkle trees and proofs for structured off-chain data.

precise-proofs supports multiple hashing algorithms. This NFT implementation uses keccak256 as the hashing algorithm for the merkle tree/proof generation.

Please read the paper on User-Mintable, Privacy-Enabled NFTs for more background on the on-chain and off-chain components and the minting process.

Tinlake uses dapp.tools for development. Please install the dapp client.

dapp update

The tests for Tinlake are written in Solidity.

dapp test

A regular expression can be used to only run specific tests.

dapp test -r <REGEX> 

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