Security mode 2 has flexible access for different security requirements. The devices recognize each other, but cannot connect to each other without authentication. InSecurity Mode 3, the security procedures are already initialized when the connection is established, which is executed with the connection key. In addition, this 128-bitencryption key is used to generate the session key or link key, which is also used to authenticate the devices.
The link key can be a combination key obtained from the key combination of two devices. It can also be a device key, a key defined for a Bluetooth device, a temporary key that can only be used for the current session, or an initialization key to protect the connection parameters during transmission.