  In the context of cloud environments, data providers entrust their data to
data consumers in order to allow further computing on their own IT
infrastructure. Usage control measures allow the data provider to restrict the
usage of its data even on the data consumer's system. Two of these restrictions
can be the geographic location and time limitations. Current solutions that
could be used to enforce such constraints can be easily manipulated. These
include solutions based on the system time, organizational agreements,
GPS-based techniques or simple delay measurements to derive the distance to
known reference servers. With D-GATE, we propose a reliable solution that uses
trusted execution environments and relies on a decentralized mesh of reference
nodes, so-called GeoClients. Here, participants periodically measure the lowest
network delay to each other to geolocate themselves. For data providers, it is
thus possible to technically attest usage control with time and geolocation
constraints without depending on centralized reference systems.
