DNS Offchain Subname Issuance - Coinbase Wallet (cb.id)
Coinbase owns the DNS name, cb.id. They have imported the name into the ENS protocol so that they can issue subnames to their users.
For example: user.cb.id
These subnames that Coinbase allows their wallet users to claim is a free ENS name. Issuance of these names does not cost gas because they are using offchain resolution. This means that cb.id stores and updates the records offchain. This is possible because of both ENSIP-10: Wildcard Resolution and EIP-3668: CCIP Read: Secure offchain data retrieval.
Wildcard Resolution and CCIP Read
Wildcard resolution allows for the creation of subnames to be done offchain, instead of on-chain which would cost gas each time a subname is created or deleted. In other words, Coinbase’s cb.id does not need to register each subname.cb.id it issues because *.cb.id wildcard resolution is supported to for ENS name lookups.
The second component involved is CCIP Read which allows a contract to fetch external offchain data. In terms of offchain data, that data is not stored on Mainnet. It is stored in an offchain location, which could be a private database server for instance. The data can also be on a Layer 2 like Optimism, which is also considered “offchain” in the context of CCIP Read, even though the data is on a blockchain.
cb.id DNS to ENS
You can see that cb.id has an Owner and Controller Ethereum address in the ENS Registry which you can view the records: ENS Manager App - cb.id on ENS. This means that cb.id is ready to be used in the blockchain, even though the name does not end in “.eth”, and DNS names are not blockchain native.
Custom Resolver
Now that cb.id was imported into the ENS registry to be used within the naming service, the Resolver record can be pointed at a custom resolver contract that supported CCIP Read.
The cb.id custom resolver contract and code can be viewed by looking up the address of 0x1934fc75ad10d7eed51dc7a92773cac96a06be56 on Etherscan.
Anytime records for a *.cb.id ENS name are requested, the custom resolver contract that cb.id points to has implemented CCIP Read (EIP 3668) and ENS wildcard resolution (ENSIP 10). It will then direct name lookups to a gateway server that implements CCIP Read (EIP 3668).
Responses from the gateway server are verified by the resolver through authorized key signing to ensure responses are not forged.
DNS to ENS Implementation with offchain Resolution
The data storage for requests are by default stored in a JSON file, but the gateway server can be configured to lookup from a variety of backend options.
If you are looking to deploy this configuration, you can visit the ENS offchain-resolver repo. The repository has an example gateway server that uses node.js. An example of a custom ENS Offchain Resolver contract that supports ENSIP 10 and EIP 3668 is also included.