ENS Offchain Resolver

This repository contains smart contracts and a node.js gateway server that together allow hosting ENS names offchain using EIP 3668 and ENSIP 10.

Overview

ENS resolution requests to the resolver implemented in this repository are responded to with a directive to query a gateway server for the answer. The gateway server generates and signs a response, which is sent back to the original resolver for decoding and verification. Full details of this request flow can be found in EIP 3668.

All of this happens transparently in supported clients (such as ethers.js with the ethers-ccip-read-provider plugin, or future versions of ethers.js which will have this functionality built-in).

Gateway Server

The gateway server implements CCIP Read (EIP 3668), and answers requests by looking up the names in a backing store. By default this is a JSON file, but the backend is pluggable and alternate backends can be provided by implementing a simple interface. Once a record is retrieved, it is signed using a user-provided key to assert its validity, and both record and signature are returned to the caller so they can be provided to the contract that initiated the request.

Contracts

The smart contract provides a resolver stub that implement CCIP Read (EIP 3668) and ENS wildcard resolution (ENSIP 10). When queried for a name, it directs the client to query the gateway server. When called back with the gateway server response, the resolver verifies the signature was produced by an authorised signer, and returns the response to the client.

Trying it out

Start by generating an Ethereum private key; this will be used as a signing key for any messages signed by your gateway service. You can use a variety of tools for this; for instance, this Python snippet will generate one for you:

python3 -c "import os; import binascii; print('0x%s' % binascii.hexlify(os.urandom(32)).decode('utf-8'))"

For the rest of this demo we will be using the standard test private key 0xac0974bec39a17e36ba4a6b4d238ff944bacb478cbed5efcae784d7bf4f2ff80.

Next, build and run the gateway:

cd packages/gateway
yarn && yarn build
yarn start --private-key 0xac0974bec39a17e36ba4a6b4d238ff944bacb478cbed5efcae784d7bf4f2ff80 --data test.eth.json

The value for the --private-key flag should be the key you generated earlier.

You will see output similar to the following:

Serving on port 8000 with signing address 0xf39Fd6e51aad88F6F4ce6aB8827279cffFb92266

Take a look at the data in test.eth.json; it specifies addresses for the name test.eth and the wildcard *.test.eth.

Next, edit contracts/deploy/10_offchain_resolver.js; replacing the address on line 9 with the one output when you ran the command above. Then, in a new terminal, build and run a test node with an ENS registry and the offchain resolver deployed:

cd packages/contracts
yarn
npx hardhat node

You will see output similar to the following:

Compilation finished successfully
deploying "ENSRegistry" (tx: 0x8b353610592763c0abd8b06305e9e82c1b14afeecac99b1ce1ee54f5271baa2c)...: deployed at 0x5FbDB2315678afecb367f032d93F642f64180aa3 with 1084532 gas
deploying "OffchainResolver" (tx: 0xdb3142c2c4d214b58378a5261859a7f104908a38b4b9911bb75f8f21aa28e896)...: deployed at 0xe7f1725E7734CE288F8367e1Bb143E90bb3F0512 with 1533637 gas
Started HTTP and WebSocket JSON-RPC server at http://127.0.0.1:9545/

Accounts
========

WARNING: These accounts, and their private keys, are publicly known.
Any funds sent to them on Mainnet or any other live network WILL BE LOST.

Account #0: 0xf39fd6e51aad88f6f4ce6ab8827279cfffb92266 (10000 ETH)
Private Key: 0xac0974bec39a17e36ba4a6b4d238ff944bacb478cbed5efcae784d7bf4f2ff80

(truncated for brevity)

Take note of the address to which the ENSRegistry was deployed (0x5FbDB...).

Finally, in a third terminal, run the example client to demonstrate resolving a name:

cd packages/client
yarn && yarn build
yarn start --registry 0x5FbDB2315678afecb367f032d93F642f64180aa3 test.eth
yarn start --registry 0x5FbDB2315678afecb367f032d93F642f64180aa3 foo.test.eth

You should see output similar to the following:

$ yarn start --registry 0x5FbDB2315678afecb367f032d93F642f64180aa3 test.eth
yarn run v1.22.17
$ node dist/index.js --registry 0x5FbDB2315678afecb367f032d93F642f64180aa3 test.eth
test.eth: 0xf39Fd6e51aad88F6F4ce6aB8827279cffFb92266
Done in 0.28s.

$ yarn start --registry 0x5FbDB2315678afecb367f032d93F642f64180aa3 foo.test.eth
yarn run v1.22.17
$ node dist/index.js --registry 0x5FbDB2315678afecb367f032d93F642f64180aa3 foo.test.eth
foo.test.eth: 0x70997970C51812dc3A010C7d01b50e0d17dc79C8
Done in 0.23s.

Check these addresses against the gateway's test.eth.json and you will see that they match.

Real-world usage

There are 5 main steps to using this in production:

1. Optionally, write a new backend for the gateway that queries your own data store. Or, use the JSON one and write your records to a JSON file in the format described in the gateway repository.
2. Generate one or more signing keys. Secure these appropriately; posession of the signing keys makes it possible to forge name resolution responses!
3. Start up a gateway server using your name database and a signing key. Publish it on a publicly-accessible URL.
4. Deploy OffchainResolver to Ethereum, providing it with the gateway URL and list of signing key addresses.
5. Set the newly deployed resolver as the resolver for one or more ENS names.