const HypercoreEncryption = require('hypercore-encryption')
const getEncryptionKey = async (id) => {
  // get key info corresponding to id...
  return {
    id, // encryption scheme
    encryptionKey // encryption key
  }
}
const encryption = new HypercoreEncryption(getEncryptionKey)
const core = new Hypercore(storage, {
  encryption: encryption.createEncryptionProvider({
    transform (ctx, entropy, compat) {
      return {
        block: deriveBlockKey(entropy),
        hash: deriveHashKey(entropy)
      }
    }
  })
})
await core.ready()
await core.append('encrypt with key')

async function getEncryptionKey (id) {
  // if id is passed as -1, the module expects the latest key
  return {
    id, // encryption id
    encryptionKey // encryption key
  }
}

{
  function transform (ctx, entropy, compat) {
    // implement custom block key derivation
    // compat will be passed as true when a compat is expected
    // block key and hash/blinding key should be distinct
    return {
      block,
      hash, // not required for compat keys
      blinding // only required for compat keys
    }
  },
  function compat (ctx, index) {
    // return true or false whether a compat key is expected
  }
}