How to use the libp2p-crypto/src/keys.unmarshalPublicKey function in libp2p-crypto

exports.createFromPubKey = function (key, callback) {
  if (typeof callback !== 'function') {
    throw new Error('callback is required')
  }

  let pubKey

  try {
    let buf = key
    if (typeof buf === 'string') {
      buf = Buffer.from(key, 'base64')
    }

    if (!Buffer.isBuffer(buf)) throw new Error('Supplied key is neither a base64 string nor a buffer')

    pubKey = cryptoKeys.unmarshalPublicKey(buf)
  } catch (err) {
    return callback(err)
  }

  pubKey.hash((err, digest) => {
    if (err) {
      return callback(err)
    }

    callback(null, new PeerIdWithIs(digest, null, pubKey))
  })
}

exports.createFromJSON = function (obj, callback) {
  if (typeof callback !== 'function') {
    throw new Error('callback is required')
  }

  let id
  let rawPrivKey
  let rawPubKey
  let pub

  try {
    id = mh.fromB58String(obj.id)
    rawPrivKey = obj.privKey && Buffer.from(obj.privKey, 'base64')
    rawPubKey = obj.pubKey && Buffer.from(obj.pubKey, 'base64')
    pub = rawPubKey && cryptoKeys.unmarshalPublicKey(rawPubKey)
  } catch (err) {
    return callback(err)
  }

  if (rawPrivKey) {
    waterfall([
      (cb) => cryptoKeys.unmarshalPrivateKey(rawPrivKey, cb),
      (priv, cb) => priv.public.hash((err, digest) => {
        cb(err, digest, priv)
      }),
      (privDigest, priv, cb) => {
        if (pub) {
          pub.hash((err, pubDigest) => {
            cb(err, privDigest, priv, pubDigest)
          })
        } else {