WN Blog 026 – 802.1x & EAP

3 min read
802.1x EAP Featured


Welcome to our latest WiFi Ninjas Blog – this time we will be covering what is 802.1X & EAP! 

802.1X is a Port Based Network Access Control, defining 3 roles: Supplicant (station, client device), Authenticator (AP or WLC) and Authentication Server (RADIUS).

Extensible Authentication Protocol (EAP) is the authentication framework supporting multiple methods such as PEAP, EAP-TLS, EAP-TTLS & more. It’s a datalink layer protocol, IP is not required. Additionally, Authenticator does not have to understand the authentication method.

RADIUS carries AAA information between Authentication and RADIUS Server.

Supplicant and Authenticator use EAPOL in wireless to exchange authentication data.

Authenticator and Authentication Server talk over RADIUS.

Both parts (EAPOL + RADIUS) form an authentication mechanism called 802.1X.

Let’s see step by step what happens in the 802.1X EAP process:

Open System Authentication:

  1. First the client and the AP go through 802.11 Open System Authentication, that is made up of 2 frame exchanges – client sends open auth to the AP & then the AP responds with open auth success.

802.11 Association:

  1. Next in the frame exchange is 802.11 Association, this is also 2 frame exchanges – client sends association request to the AP & then the AP responds with an association response.

802.1x EAP Authentication (below is based on EAP-TLS, but it will be similar for other EAP methods):

  1. Now we move on to the juicy part of the frame exchanges – “802.1X EAP authentication”. The first frame in this exchange is from the client which sends an “EAPOL start message” to the AP to start EAP authentication.
  2. The client is then asked for its identity in an “EAP Request/Identity” message from the AP.
  3. The client replies with an “EAP Response/Identity” message with its (dummy) user ID and the request to use TLS, which is forwarded to the RADIUS server.
  4. The RADIUS server, upon receiving the RADIUS access request & RADIUS access challenge (EAP Response/Identity message), starts the server-side TLS process by sending an EAP-TLS Start message to the client. 
  5. The client responds with an EAP response – client hello message.
  6. The RADIUS server replies with an EAP Request message— a TLS server hello. It provides its certificate to the client, TLS protocol version, a cipher suite, and the client requests the certificate. 
  7. The client validates the server certificate and responds with an EAP Response message that contains its certificate. This message starts the negotiation for cryptographic specifications – the cipher and compression algorithms.
  8. After the client certificate is validated, the RADIUS server responds with cryptographic specifications for the session. 
  9. The client responds with an EAP-Response packet of EAP-Type = EAP-TLS with no data, notifying the RADIUS server that it has received the cryptographic specifications. 
  10. The RADIUS server sends an EAP-Success message to the AP indicating successful authentication.  
  11. The RADIUS server creates the session Master Key, also known as the PMK (Pairwise Master Key). 
  12. The client also creates the PMK. 

4-Way Handshake:

  1. The client and the AP run the 4-way handshake to create the session keys. Which are:
    • EAPOL Key Packet No.1(Authenticator Nonce) – Client calculated PTK
    • EAPOL Key Packet No.2 (Supplicant Nonce, MIC) – Authenticator calculated PTK
    • EAPOL Key Packet No.3 (Install PTK, MIC, Encrypted GTK)
    • Now we have the GTK (Group Temporal Key) encrypted in the PTK.
    • EAPOL Key Packet No. 4 (MIC)
  2. Voila! We now have fully established an encrypted 802.1X EAP-TLS session!

We have also made a diagram of the process so you can visualise the above a bit easier! 

We hope that you found this blog helpful for you and always give us a shout if you need anything else!

Tons of love,

WiFi Ninjas x 

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