proofdrop

Mint a tamper-proof, anonymous, on-chain receipt of any data you want permanently witnessed.

ProofDrop is a minimal ERC-721 contract that lets anyone pay a small fee to mint an NFT whose token URI points to immutable, decentrally-stored metadata (typically Arweave JSON). The mint transaction itself becomes the proof: public, timestamped by the chain, untamperable as long as the chain exists.

Why

• Whistleblower receipts — pin a document hash on-chain so its existence at a specific timestamp can be verified later, even if the original is taken down.
• Research / IP priority — establish "I had this idea on this date" without trusting a registrar, lawyer, or notary.
• Censorship-resistant witness records — testimony, evidence, journalism artifacts that survive platform takedowns.
• Just decentralization — no account, no KYC, no trust beyond the chain.

If a centralized service can revoke your proof, it isn't proof. Mint and the record outlives any single actor.

How it works

1. You upload your data (or its hash) to immutable storage — Arweave, IPFS-pinned, or another permanent store. You get back a URI.
2. You call mint(tokenURI) with 0.005 ETH. The contract issues an NFT in your wallet whose tokenURI points at that data.
3. The transaction is the receipt. Block height, timestamp, sender, token URI — all immutable on-chain.

function mint(string memory tokenURI) external payable returns (uint256) {
    require(msg.value >= 0.005 ether, "Minting costs 0.005 ETH");
    tokenCount++;
    _safeMint(msg.sender, tokenCount);
    _setTokenURI(tokenCount, tokenURI);
    return tokenCount;
}

Stack

• Contract: Solidity ^0.8.0 · OpenZeppelin ERC721URIStorage + Ownable
• Tooling: Hardhat
• Networks (configured): localhost · Polygon Amoy testnet
• Frontend: vanilla JS (frontend/)

Quick start

Prerequisites

• Node.js 18+
• Yarn (or npm)
• MetaMask or any Ethereum-compatible wallet

Setup

git clone https://github.com/ZNav/proofdrop.git
cd proofdrop
yarn install

Create a .env (gitignored — never commit):

PRIVATE_KEY=your_wallet_private_key
ALCHEMY_API_KEY=your_alchemy_key

Deploy locally

npx hardhat node                                 # in one terminal
npx hardhat run scripts/deploy.js --network localhost

Deploy to Amoy testnet

npx hardhat run scripts/deploy.js --network amoy

Save the deployed address — that's your contract.

Mint a proof

// scripts/testMint.js
const hre = require("hardhat");

async function main() {
  const [user] = await hre.ethers.getSigners();
  const contract = await hre.ethers.getContractAt(
    "ProofDrop",
    "<YOUR_DEPLOYED_CONTRACT_ADDRESS>"
  );

  const tx = await contract.mint("https://arweave.net/<your-data-hash>", {
    value: hre.ethers.utils.parseEther("0.005"),
  });
  const receipt = await tx.wait();
  console.log("Minted. Tx hash:", receipt.transactionHash);
}
main().catch(console.error);

npx hardhat run scripts/testMint.js --network localhost

Repository layout

contracts/ProofDrop.sol     # the contract
scripts/deploy.js           # deployer
frontend/                   # vanilla JS minting UI
hardhat.config.js
test-env.js                 # network sanity check
validate.js                 # post-deploy contract validation

Notes & caveats

• Mint cost: 0.005 ETH (or chain-equivalent). Owner can withdraw() the collected balance.
• Permanence depends on the data layer, not just the chain. The on-chain token URI is forever; whether the data behind that URI stays accessible is on the storage provider. Arweave's "pay once, hosted forever" model is the recommended target for the metadata.
• Anonymity is only as good as your wallet's anonymity. Use a fresh address for sensitive proofs and consider a privacy chain or mixer-aware workflow.
• Gas costs vary by chain. Amoy is testnet (~free); mainnet Polygon or Ethereum will cost real money to deploy and mint.
• Never commit your .env.

License

MIT — see LICENSE.