This is something that keeps coming up while studying for different certifications and I always have to review everything, flip through the pages since there are technically 3 sections here, I decided to write up a quick overview of all 3 including the flow as shown in the diagram below. When a Wireless Client connects it has to go through the initial connection process Machine State. In this process, there are 2 key devices that play a role. Station and an Access Point:
- Probe Request
- Probe Response
- Authentication Request
- Authentication Response
- Association Request
- Association Response
Once Machine State completes client next goes through the EAP process. In this process there are 3 main devices. Supplicant (Client), Authenticator (AP), Authentication Server. Initially client and server will exchange messages via authenticator with some basic Identity check. Then they will establish a secure and encrypted tunnel and real credentials will get exchanged. At the end of this process server will either send a success or rejection. At the same them MSK (512bit)/PMK (PSK, 256bit) will be derived from this process as well.
Last state is the 4-Way Handshake. Supplicant, Authenticator are the 2 main devices that play their part. Using Master Session Key (MSK) –> Pairwise Master Key (PMK) and Group Master Key (GMK) are generated. GMK generates Group Temporal Key (GTK). PMK generates Pairwise Transient Key (PTK). Once all keys are installed and client confirms it controlled port gets unblocked and client is now successfully connected to the wireless LAN.
NOTE: This is a very high level overview for my notes. There are additional details related to different type of EAP that go further into details of that process. If you notice any mistakes or have any questions/suggestions please feel free to leave feedback, there is always room for improvement. Thank you.