code: function encrypt (plaintext, key, nonce, algo = DEFAULTS.crypto.symmetric_alg) {
    if (!CRYPTO_FUNCTIONS[algo]) throw new Error(algo + ' is not available')
    return CRYPTO_FUNCTIONS[algo].encrypt({ plaintext, nonce, key })
  }
docs: Symmetric private key encryption using secret (derived) key.
  @param {buffer|string} plaintext Data to be encrypted.
  @param {buffer|string} key Secret key.
  @param {buffer|string} nonce Randomly generated nonce.
  @param {string=} algo Encryption algorithm (default: DEFAULTS.crypto.symmetric_alg).
  @return {buffer} Encrypted data.