Generate onion v3 address from ed25519 public key

onion.js

// npm install hi-base32 sha3

const base32 = require("hi-base32");
const { SHA3 } = require("sha3");

function verifyOnionAddress(addr) {
  const suffixLength = ".onion".length;
  if (!/\.onion$/i.test(addr) || addr.length != 56 + suffixLength) {
    return false;
  }

  let base32Encoded = addr.substr(0, addr.length - suffixLength).toUpperCase();
  let decoded;
  try {
    decoded = Buffer.from(base32.decode.asBytes(base32Encoded));
  } catch (err) {
    return false;
  }

  const version = decoded.slice(decoded.length - 1);
  if (!version || !version[0] || version[0] !== 3) {
    return false;
  }

  const checksum = decoded.slice(decoded.length - 3, decoded.length - 1);
  const pubkey = decoded.slice(0, decoded.length - 3);

  const hash = new SHA3(256);
  hash.update(Buffer.from(".onion checksum"));
  hash.update(pubkey);
  hash.update(version);
  const calculatedChecksum = hash.digest().slice(0, 2);
  return calculatedChecksum.toString("hex") === checksum.toString("hex") ? pubkey : false;
}

function encodeOnionAddress(pubkey) {
  const version = Buffer.from([0x03]);

  const hash = new SHA3(256);
  hash.update(Buffer.from(".onion checksum"));
  hash.update(pubkey);
  hash.update(version);
  const checksum = hash.digest().slice(0, 2);

  const decoded = Buffer.concat([pubkey, checksum, version]);

  return base32.encode(Array.from(decoded)).toLowerCase() + ".onion";
}

let address = "pg6mmjiyjmcrsslvykfwnntlaru7p5svn6y2ymmju6nubxndf4pscryd.onion";

let publicKey = verifyOnionAddress(address);
console.log(encodeOnionAddress(publicKey));
console.log(encodeOnionAddress(publicKey) === address);