master key (802.11i) (MK)
A master key(MK) always indicates a key hierarchy. The subordinate key or keys are derived from such a master key.
802.11i, which has a revised security concept compared to 802.1x, is an example of a key hierarchy with a master key and several keys derived from it. In 802.11i, the Pairwise Master Key( PMK) is derived from the master key, which in turn is used to derive the Pairwise Transient Key( PTK) and other keys.
To ensure network security in 802.11i, the standard includes key management, in which the authentication server( AS) first generates a master key (MK) upon successful authentication, which it transmits to the WLAN end device. This master key represents the positive access decision between the authentication server and the WLAN end device and is known only to these two. It is used exclusively for the first session between the two units.