In trusted environments, e.g., smart homes, the establishment of security for IoT devices is well understood. However, the emergence of other private and industrial mobile use cases, such as pet monitoring or container and parcel tracking, involve IoT devices that operate in untrusted networks, e.g., using public Wi-Fi or ad-hoc networks for Internet access. Inevitably, new risks come up in these environments. First, the relationship between communicating parties reveals private or secret routines  and, combined with location data, eases theft of valuable goods. Second, IoT devices in untrusted networks lack either a globally routable IP address or traditional defense mechanisms such as firewalls and intrusion detection systems.