Data in vehicle networks has been treated as proprietary assets, due to car makers' concern of potential IP infringement via extraction of confidential vehicular data. To address this concern, an intermediate gateway in between internal and external networks translates proprietary in-vehicle data to rich type data, thus preventing the exposure of raw in-vehicle data. The translation relies solely on the gateway which can be a direct target of cyberattacks, making it difficult to trust the data through the gateway. This, in turn, requires authentication of the translated data. A communication protocol is presented that provides secure communications between the vehicle's internal components and external entities. The protocol enables authorization of external servers for in-vehicle ECUs as well as authentication and proof of messages between internal and external components to combat a compromised gateway.