A device authentication server authenticates a remotely located device using unique data associated with the user of the device stored on a remotely located server that has an established relationship with the device, such as client logic installed on the device and authentication data of the user stored on the device. The unique data can be unique metadata associated with inter-person messages. Since each user receives and sends a unique collection of messages, the unique message meta-data associated with a user's account is, in aggregate, unique.