Location brokering technique embodiments are presented that employ sensor data captured by a user's mobile device to determine the device's location, encrypt the location data and store it in a database. The location data is encrypted in such a way that it is possible to determine when a user's mobile device is currently in the same vicinity as another user's mobile device who is a member of the same group. However, the actual location and relative mobility or immobility of the users cannot be ascertained except by the users themselves via a decryption procedure or by trusted components. Services are provided can read the stored encrypted location data, processes it to determine if group members are in the same vicinity, and either respond to user queries about the location of other members of a group the user belongs to, or push this information to appropriate users.