# key hierarchy management and master key

I have this equation, $E_{K_{as}}(E_{K_{bs}}(K_{ab}))$ which means $K_{ab}$ is encrypted by $K_{bs}$ then whole packet is encrypted by $K_{as}$.

I think the key structure is $K_{as}$ is the master key, $K_{bs}$ is under $K_{as}$ and $K_{ab}$ is the session key.

My question is: if I have two long term keys and one session key, can I make both long term keys to be the master key? Or only one out of two of them can be the master key?

• the nomenclature does not imply that any one of those is a master key or even a long term key. In fact, I would say that 'ab' is a session key, 'bs' is a signing key of party b, and 'as' is a signing key of party a – Richie Frame Apr 20 '16 at 2:12
• @RichieFrame link(postimg.org/image/nfbb6lck7) contains a full picture of the protocol. As the pictures shown, are K_as and K_bs both master keys? – Ricky Apr 20 '16 at 4:28
• That protocol diagram is a mess. What is S? What does it do? What is N? What was talked about in "last lecture"? – Richie Frame Apr 20 '16 at 6:18