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Bluetooth security is very important to allow keyless doors and automatic billing super stores. At link layer it is maintained by authentication and encryption. First a device does authentication by issuing a challenge and other device has to then send a response to that challenge. The BD-ADDR and link key is shared between them. After authentication encryption may be used to communicate. There are four types of keys: combination, unit, temporary and initialization.
Link Manager and controller
Link manager is used for managing the security, link set-up and control. It communicates with other link manager to exchange information and control messages through link controller by using some pre-defined link level commands. Once the connection has been setup, it can have up to three SCO connections created across it, or its mode can be changed, either to a low power mode or to a test mode (these are useful for certification of Bluetooth devices by testing authorities and for a manufacture’s production line testing of devices). When the connection is no longer required, LMP can cause disconnection.
It has less support for upper layers but it can be improved by using a upper layer interface which allows it to execute algorithms for mode management (park, hold, sniff, active), security management, QoS etc. For example if user requests low power then link manager can negotiate with other link manager about the power control and both can go into the same mode according to the pre-set algorithm
The Link Manager (LM) converts the commands into operations at the Baseband level, managing the following operations.
1) Attaching slaves to Pico-nets, and allocating their active member addresses.
2) Breaking connections to detach Slaves from a Pico-net.
3) Configuring the link including Master/Slave switches
4) Establishing ACL and SCO links.
5) Putting connections into Low Power modes: Hold, Sniff and Park.
6) Controlling test modes.
It is a process of identifying a device in a network usually based on username and password to ensure security. It is also a way to allow devices in a networked system to gain the access to the other device. The link manager protocol ensures the authentication in the Pico-net or scatter net.
The translation of data into a secret code is known as encryption. It is the most effective way to achieve data security because we need a secret key or password that enables to decrypt it. Unencrypted data is plain text while decrypt is called cipher text.
Apart from authentication and encryption there are many other functions as shown in figure.
All the functions are specified below.