Good Morning all
I am trying to understand the process used that allows a client to connect to a WPA2 wireless network. I have searched and found many resources but I can't seem to gel it together. So a little help would be appreciated, in particular I'm not clear on what happens after a probe-response or beacon has been received by a client.
My understanding so far:
Beacons sent by an AP or probes sent by a cleint allow the discovery of available WLANs, within the beacon / probe-responses are the names of the WLANs and the security they use; WPA, WPA2, Enterprise etc.
I understand how the WPA 4 way handshake works ( to a degree ) but what's happening in the interim of 'clicking connect' on the client and the start of the 4 way handshake?
The reason I ask is that whilst reading info on how the 4 way handshake works it occoured to me that when the nonce and snonce are being sent between client and AP to create the keys for encryption they are 'exposed', unless there is already some form of encryption taking place?
Here is a good reference for the above topic.
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Great question .. This is complicated stuff and normally people don’t dive this deep.
Once the probe, authentication (not security authentication btw this is open / shared) and association are complete the ap and station move to the 4 way should WPA/WPA2 / PSK or WPA/WPA2 Enterprise is configured.
The handshake is the same if its a PSK or 802.1X.However the orignal keying material used to start the authentication process is derived differently. The PSK uses the actual phase phrase for seeding material in the 4 way key handshake.While the radius server uses a random AAA key generated during the EAP process. This keying material is used for the seeding martial in the 4 way handshake.
5 Things are needed for the handshake -
PSK or Master Key
S mac address
A mac address
The Ap sends the first handshake. Inside this frame is its Anonce and mac address both derived from the PSK or Master Key. The client at this point has the UNICAST keying material, because it knows its own Snonce and S mac address. The client then sends its Snonce and S mac address derived from the PSK / Master key to the AP. The Ap now has enough to derive the key for UNICAST.
Both transactions are encrypted with a KCK,KEK, TL, keys. Going off memory here…
The 3rd and 4th handshakes are for the broadcast key.
Hope this helps ..
Yes CWSP is a great book. Here is a blog post I wrote on the subject
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