96	Bluetooth Security

request, the service manager will use the PSM value to identify which higher layer protocol a connection request belongs to. With this information available, the correct security policy settings can be applied to the connection request. More information may also be stored, such as a human-readable service name. The service database can store its information in nonvolatile memory, or it is required that services register at every boot instance.

The service manager is responsible for maintaining the device database. It must be updated every time that a bonding with a device takes place. For new devices, a new record is generated. If existing link keys are changed, the device database must be updated accordingly. Changing the trust level of a device (untrusted to trusted or vice versa) must be reflected in the database. Should the local device be set into security mode 3 (i.e., link level–enforced security), it is possible to utilize the security manager for this also. Then, in order to avoid untrusted devices getting unwanted access to local services, the security manager should remove all existing link keys for untrusted devices.

Security information pertaining to services or applications need to be registered with the security manager for inclusion in the service database before a service is accessed. This can be done by the applications themselves or by designated security delegates. Registration includes security levels for incoming and outgoing requests, protocol identification, and the PSM used at the L2CAP layer. Additionally, multiplexing protocols such as RFCOMM also need to register with the security manager.

Reference

[1] Müller, T., ed., “Bluetooth Security Architecture,” White Paper Revision 1.0, Bluetooth Special Interest Group, July 1999.