Hi,
I was trying to interpret the exact meaning of a trusted and untrusted Bluetooth device. The Bluetooth Security Architecture whitepaper on the SIG site(https://www.bluetooth.org/foundry/sitecontent/document/whitepapers_presentations) mentions the following on Page 14:

3.2.2 Device Trust Level
We distinguish between two different device trust levels:
Trusted Device: The device has been previously authenticated, a
link key is stored and the device is marked as
“trusted” in the Device Database.
Untrusted Device: The device has been previously authenticated, a
link key is stored but the device is not marked as
“trusted” in the Device Database.
Unknown Device: No security information is available for this
device. This is also an untrusted device.


From this I would interpret that if pairing successfully happens between two devices, then usually the target device should be marked as "trusted" in the device database.
I do not understand in which case, the device database would mark the status as "untrusted" for a device which has been successfully paired and the link key has been already stored.

On Page 9 of the same document, the trust levels are distinguised as:
- Trusted Device: Device with fixed relationship (paired) that is
trusted and has unrestricted access to all services.
- Untrusted Device: Device with no permanent fixed relationship
(but possibly a temporary one) or device that has a fixed
relationship, but is not considered as trusted. The access to
services is restricted.


i do not understand the "Untrusted Device" Section-particularly, what is a "Device with no permanent fixed relationship" or "device that has a fixed relationship, but is not considered as trusted". What is the criteria to "consider a device as trusted or untrusted"?

Please help.