Bluetooth key management

Bluetooth key management
Like WPA2, Bluetooth also relies on effective key management where again numerous
keys are used in combination to ensure data encryption and integrity. We have
already introduced a few significant keys that are used during the authentication and
pairing procedures. In this section we shall introduce the remaining set of keys that
are also used within the encryption procedure. The link key, which is made up of a
128-bit random number, was introduced as a key whose primary role was to determine
if two or more devices had a previous relationship and, as such, if no relationship
existed a key would be generated. The link key also plays a significant role within
the encryption process and, in fact, there are four types of link keys available, as shown
in Table 4.1 (the unit key has now been deprecated as there were some security concerns
regarding its usage within the Bluetooth implementation; this is something we  will touch upon in a moment). Additionally, there is an encryption key (KC), which
is derived from the current link key and is used whenever the encryption procedure is
requested.
The combination key, as the name suggests, is generated as a combination of two
Bluetooth devices, for example, device A and device B. And, for each new combination
of device, then a new key is created. The unit key is interchangeably used with
the combination key, but what distinguishes them both is the procedure used to initially
create them. The unit key is generated when a Bluetooth device is installed and
it is the type of application, subject to memory and storage constraints, that prescribes
what key should be used (combination or unit). Since the unit key is generated only
once at installation and, as such, remains fairly static throughout the lifetime of the
product, this has led to its being considered unconfident in nature as a key for encryption.
Instead, the combination key should be used for a more secure working environment
and, evidently, more storage would be made available to these keys as they are
continually generated when introduced to new devices.