L402-over-eth-Layer2

What it claims

L402-EL2 keeps the L402 wire format, so existing L402 parsers still work, and replaces Lightning invoices with a unidirectional payment channel on an Ethereum L2. The author's stated results:

• On-chain cost: each channel lifecycle needs 2 on-chain transactions (open and settle), not one per call.
• Latency: payment adds under 10 ms per request. Paying on-chain per call would add about 1–2 s and cost more in gas than the service.
• Token: any ERC-20 works. The author uses wrapped BTC (cbBTC, WBTC, tBTC) so prices match their Lightning side.

How it works

• Channel ID: channelId = keccak256(abi.encode(payer, provider, token)). Either side can compute it offline before the channel exists.
• Voucher: each call signs Voucher(channelId, cumulativeAmount, nonce, validUntil) with EIP-712. The amount is a running total, which has three effects:
• old vouchers cannot be replayed;
• the server stores one row per channel;
• verification is an in-memory signature check of about a millisecond, with no RPC call.
• Session keys: authorizeSigner(key, maxCumulative, validUntil) puts the spending cap in the contract rather than the client.
• 24h challenge period: revoking or tightening a session key waits the same 24h as a channel close. This stops a payer from voiding vouchers the provider has already served.
• Deposits: besides normal deposits, single-signature deposits via ERC-2612 and ERC-3009 are supported.
• Settlement: a separate settler submits the latest voucher for many channels in one settleBatch() call.

sequenceDiagram
  participant A as Agent
  participant P as Provider
  participant C as L402Escrow (L2)
  A->>C: open prefunded channel (tx 1)
  loop per paid MCP call
    A->>P: request
    P-->>A: 402 challenge
    A->>P: retry + macaroon + cumulative voucher
    P->>P: in-memory sig check
  end
  P->>C: settleBatch latest vouchers (tx 2)

How to use it

The page says the repo contains:

• the L402Escrow.sol contract, with node and Foundry tests, including fuzzing;
• TypeScript server, client and settler packages;
• a protocol spec;
• an end-to-end example that runs on an in-process EVM with no configuration.

The page gives no install commands or licence. The project site is https://www.l402-over-eth-l2.com/.

Limits

• Not audited. The author says not to use it with real funds yet.
• Early-stage feedback request. The author describes themselves as less expert in payment channels, EIP-712 and account abstraction than the forum audience, and says they wrote it with LLM help.
• Funds lock-up. Closing a channel and revoking a session key both wait 24h, so neither takes effect immediately.
• Conflict of interest. The author is LightPhon's founder and plans to use the system there.
• No independent measurements. The <10 ms and ~ms verification figures are the author's claims. The page gives no benchmark setup.