Namehashing is an algorithm that converts a domain name in a classical format (like www.example.crypto) to ERC721 token id. All .crypto ecosystem contracts accept a domain name as a method argument in the form of an ERC721 token. Namehashing is defined as a part of the EIP-137 standard. See the standard for a text description of the algorithm.

One can verify his implementation of the namehash algorithm using the following reference table:

Reverse lookup

Fundamentally namehashing is built to be a one-way operation. It recursively hashes the labels using the SHA-256 hash function.

If one possesses a precomputed table of all hashes and corresponding domains reverse lookups are possible. This table can be reconstructed using the events on the CNS Registry NewURI event.

JSON RPC

The .crypto registry remembers all the domain names that were ever minted with their corresponding namehash: source code. That makes it possible to obtain an original domain name from a namehash via ETH RPC call to Registry#tokenURI.

Public API

There is a way to obtain domain information by namehash from APIs. To do this you need to call https://unstoppabledomains.com/api/v1/{namehash}

Example:

GET request: https://unstoppabledomains.com/api/v1/0x0f4a10a4f46c288cea365fcf45cccf0e9d901b945b9829ccdb54c10dc3cb7a6f​

Response:

{
  "addresses": {},
  "whois": {},
  "ipfs": {},
  "gundb": {},
  "social": {},
  "meta": {
    "owner": "0x000000000000000000000000000000000000dead",
    "type": "CNS",
    "ttl": 0,
    "domain": "crypto",
    "namehash": "0x0f4a10a4f46c288cea365fcf45cccf0e9d901b945b9829ccdb54c10dc3cb7a6f"
  },
  "records": {}
}