sameerdewan / eth-arbitrum-poe

proof of existence on ethereum using l2 arbitrum

eth-arbitrum-poe

The eth-arbitrum-poe repository is free to fork and use by anyone, anytime.

ProofTokens are NFTs that are minted to represent proof of existence. The underlying contract for the ProofToken is written in Solidity, and can be deployed to any EVM friendly environment. The minter of a ProofToken must provide the mintProofToken() function one parameter - a bytes32 hash of the item that a proof is being generated for, and two optional parameters, a bytes32 hash of the item's off-chain URI resource, and a string of the off-chain resource.

Example 1: Only bytes32 hashValue of desired item proof provided

async function mintProofToken(fileAsBuffer) {
    // assumes global constant for web3 deployed contract = "Contract"
    // assumes global hashing library "sha256"
    // The ProofToken NFT generated is sent to the sender
    // The contract emits an event "ProofTokenMinted"
    const hashValue = sha256(fileAsBuffer);
    const from = '0x07e07586A6433b65218f57010b026AbB66B7F2B2';
    await Contract.methods.mintProofToken(hashValue).send({ from });
}

Example 2A: All three parameters provided (hashValue, URIHash, URI)

async function mintProofToken(fileAsBuffer) {
    const hashValue = sha256(fileAsBuffer);
    const URIHash = '01ec6108ec8c21ca933f0ee001b1b202';
    const URI = 'https://www.example.com/path/to/metadata.json';
    const args = [hashValue, URIHash, URI];
    const from = '0x07e07586A6433b65218f57010b026AbB66B7F2B2';
    await Contract.methods.mintProofToken(...args).send({ from });
}

Example 2B: All three parameters provided (hashValue, URIHash, URI), but attaching an X12 EDI formatted basic invoice as the URI parameter, storing it on chain in the tokenURI field for the ERC721

async function mintProofToken(fileAsBuffer) {
    const hashValue = sha256(fileAsBuffer);
    const x12EDI = 'ST*810*0001~BIG*20000513*SG427254*20000506*508517*1001~N1*ST*ABC AEROSPACE CORPORATION*9*123456789-0101~N3*1000 BOARDWALK DRIVE~N4*SOMEWHERE*CA*98898~ITD*05*3*****30*******E~IT1*1*48*EA*3**MG*R5656-2~TDS*14400~CTT*1~SE*10*0001~';
    const x12EDIHash = sha256(x12EDI);
    const args = [hashValue, x12EDI, x12EDIHash];
    const from = '0x07e07586A6433b65218f57010b026AbB66B7F2B2';
    await Contract.methods.mintProofToken(...args).send({ from });
}

The ProofToken contract inherits from the ERC721URIStorage OpenZeppelin contract. The burnable function is thus inherited, however, is overridden in the contract to both burn the token and remove it from contract state as an existing hash. The overridden burnable function is still only callable by the owner of the token.

The ProofToken NFT itself does not need to be owned to validate the existence of a proof on chain. The existence of a proof can be checked by calling the contract method get() with the bytes32 hashValue of the item to be validated, returning true for proof of existence found, and false for not found.

Example 3: Validating a hash (proof)

async function main(hashProof) {
    const exists = await Contract.methods.get(hashProof).call();
    if (exists) {
        alert('Proof of existence validated!');
    } else {
        alert('Proof of existence could not be found.');
    }
}

Proof tokens act as records in themselves of a proof of existence of a given item. Given that guessing the correct input of a SHA-256 hash is around one in quattuorvigintillion (78 digit number), the combined ownership of a token and earliest blockchain persisted record could serve to act as a representive tokenized version of the underlying item.

With that being said, the significance and use of the ProofToken contract, this repository, and the ProofToken NFTs themselves, is open to the end user.