code: func initNonce(dst []byte) {
  	// NOTE: bts does not escapes.
  	bts := make([]byte, nonceKeySize)
  	if _, err := rand.Read(bts); err != nil {
  		panic(fmt.Sprintf("rand read error: %s", err))
  	}
  	base64.StdEncoding.Encode(dst, bts)
  }
docs: // initNonce fills given slice with random base64-encoded nonce bytes.