code: func (cs *ChaChaStream) Unpack(payload string) []byte {
  	decoded, _ := base64.StdEncoding.DecodeString(payload)
  
  	data := make([]byte, len(decoded))
  	cs.cipher.XORKeyStream(data, decoded)
  	return data
  }
docs: // Unpack returns the payload as unencrypted byte array