How can Eve identify that an 80211 frame is an authenticatio

How can Eve identify that an 802.11 frame is an authentication challenge or response? Explain your answer.

Solution

There are generally 2 types of authentication when we use 802.11 Wireless technology:

Before heading into the details of the different types of Authentication, let\'s try to analyze the frame format of the management frames in 802.11.

The frame body (excluding the MAC header) consists of mainly of 4 fields (Rest are not so important in relevance to this question):

Open System Authentication is a very simple type of Authentication where a request is generated by the client to the access point called the Authentication Request and the access point always successfully authenticates the client and sends back an Authentication Response. Note that this is a very simple process not involving any exchange of keys and the access point allows every client to authenticate.

Shared Key Authentication is a more complex type of authentication involving an exchange of a shared key and challenge text. The Shared Key Authentication involves a 4-way handshake which is of the following order:

So, there is a small doubt in the question asked.

What do you mean by Authentication Challenge? Are you talking about Authentication Response with Challenge or Authentication Request with encrypted Challenge?

Anyways, I’ll answer for both.

After you capture the Management Frames of 802.11, if you look into the frames you will find 4 types of packets as mentioned earlier.

If you look into the Authentication Algorithm field and find it as 1, then we are using Shared Key Authentication.

If the Authentication Sequence number is 1, it is an Authentication Request.

If the Authentication Sequence number is 2, check that you will have a Challenge text. Notice that the packet is from the Access point to the client. This is Authentication Response with Challenge.

If the Authentication Sequence number is 3, you will see an encrypted Challenge text send from Client to Access Point. This is Authentication Request with encrypted Challenge.

Finally, If the Authentication Sequence number is 4, this is Authentication Response. Note that the status code if zero implies Successful Authentication.