NFT Certificates

After a batch is finalized, users can claim an ERC-721 NFT certificate that serves as a visual, on-chain proof that their content hash was anchored on L1 Ethereum.

Claiming

Users call claimNFT on the L2AnchoringManager:

function claimNFT(
    bytes32 attestationId,
    uint256 batchStartIndexHint
) external nonReentrant

Requirements

1. The attestation must exist and be mapped to a queue index.
2. The queue index must be confirmed (index < confirmedIndex).
3. The NFT must not already be claimed.
4. The batchStartIndexHint must point to the correct batch containing this index.

Minting

The token ID equals the queue index. The NFT is minted to the original attester (the address that created the EAS attestation), not necessarily msg.sender.

On-Chain Metadata

The tokenURI function generates fully on-chain metadata — no IPFS or external hosting required:

function tokenURI(uint256 tokenId) public view returns (string memory)

It returns a data:application/json;base64,... URI containing:

{
  "name": "Certificate #<tokenId> - <l2Name>",
  "description": "Proof of content existence at timestamp ...",
  "external_url": "https://timestamps.now/<chainId>/<tokenId>",
  "image": "data:image/svg+xml;base64,...",
  "attributes": [
    { "display_type": "date", "trait_type": "date", "value": <unix_timestamp> },
    { "trait_type": "l1BlockNumber", "value": "<block>" },
    { "trait_type": "l2BlockNumber", "value": "<block>" }
  ]
}

SVG Generation

The NFTGenerator contract produces a complex SVG certificate design entirely on-chain. The visual includes:

• Gradient background with animated glow effects.
• Grid pattern overlay.
• Tree diagram symbolizing the Merkle tree structure.
• Certificate ID (token ID with comma formatting).
• Content hash displayed as two lines of 32 hex characters.
• L2 block number of the original submission.
• L1 block number of the anchoring transaction.
• Timestamp formatted as YYYY-MM-DD HH:MM:SS (using Solady’s DateTime library).
• Code 128-C barcode encoding the token ID.
• “UNIVERSAL TIMESTAMPS PROTOCOL” watermark.

Code 128-C Barcode

The Code128CGenerator contract generates a Code 128-C barcode as an SVG element:

1. The token ID is zero-padded to 20 digits.
2. Digits are grouped into pairs (Code 128-C encodes two digits per symbol).
3. A checksum is calculated using the Code 128-C weighted sum algorithm.
4. The barcode is rendered as alternating white and blue bars in an SVG <g> element.

This allows the certificate to be scanned and linked back to the on-chain record.

Design Rationale

Generating NFT metadata on-chain (rather than pointing to IPFS) ensures:

• Permanence: The metadata cannot disappear if an IPFS pin is removed.
• Trustlessness: Anyone can verify the metadata by calling the contract directly.
• Consistency: The visual representation always matches the on-chain state.

The SVG for the NFT is generated every time the tokenURI is called.