In the past we have written a couple articles on using tshark to strip WPA capture files down to a specific ESSID or SSID but in some cases it can be more useful to strip the capture down by BSSID or MAC address of the WAP. Isolating packets by BSSID or WAP MAC address is useful in a scenario where a wireless deployment has numerous WAP’s and you have captured a specific SSID’s traffic from more than one WAP. Below is information on how to strip down a capture file based on BSSID and information on capture size before stripping the file down.
It is possible to crack WPA/WPA2 wireless network credentials using any number of open source tools available now including oclHashcat+, aircrack-ng, or pyrit to name a few. If you are having trouble cracking a password it is possible that the network uses RADIUS authentication instead of pre-shared keys(PSK). Now you could see this when if you looked at the details of the network you were attempting to capture authentication packets for as it would display as WPA Enterprise versus WPA Personal. It definitely happens though that this is not considered during the capture so you may need to verify that a network is WPA/WPA2 Personal versus WPA/WPA2 Enterprise once you are attempting to crack the authentication. You can do this using Wireshark and the details below.
It is very common when obtaining wireless network handshakes to end up with a huge capture(.cap or .pcap typically) file. Previously purehate wrote this article on filtering out SSID specific EAPOL packets from a capture file but if you wanted to keep any and all packets related to a specific SSID including data packets, beacon frames, etc. the below tshark command will accomplish that. This is very similar to the previous article but will provide more data for the user and still slim down a capture file if you had packets from multiple SSID’s.
A while ago I wrote a short tutorial on how to strip down a wireless capture which contained a wpa handshake so that only eapol packets and beacon frames where left. I have since found a little bit better way to do it so I decided to make a new post. In the previous article I showed how to strip by wlan.mgt frames containing the mac address. The problem with this is that it strips out lots of other packets which some programs use to check for ESSID. I looked into the issue some more and found a way to strip just by essid.
I recently had a customer upload a WPA capture to our tools.question-defense.com server which failed immediately. This can happen from time to time and is for a variety of reasons Sometimes if captures does not contain all 4 eapol packets they will fail , and sometimes if a capture has lots of other wifi garbage in the .cap file it can confuse the cracking program. This last time was a new situation. After the fail I analyzed the cap file and determined that the essid was not present in the capture. This is absolutely crucial for the decrypting process. In this short article I will show how I determined the essid was not present and what I did about it.