The other day I had a wireless network packet capture file saved as a .cap file. The ESSID that was displaying via normal aircrack-ng output of the WPA/WPA2 wireless packet capture lead me to believe there was at least one space included in the beginning of the ESSID and likely after the ESSID since it was not processing properly using oclHashcat-plus. I had never run into this before so wasn’t exactly sure the easiest way to figure out the number of spaces so I posed the question in the Freenode aircrack-ng IRC channel and got a couple responses which are noted below as well as instructions following the clearest solution.
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 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.
In my previous article I was building SIPcrack from source on the Ubuntu 10.04 platform. I ran into a few erros during the build. The first error is explained here but after that I ran into one more. Below I describe how to get past the pcap.h error. This fix should work on any version of ubuntu that is giving you a pcap.h missing error.
Sometimes you have a very large capture file and would like to extract the WPA/WPA2 handshake packets from it to a separate file. The can be done with “tshark” which is a command line version of the Wireshark suite. Installing the linux version of the Wireshark suite on your system should also install tshark.
**NOTE** This article is outdated please read this article instead for a much easier method for extracting WPA handshakes for specific SSID’s from large WPA/WPA2 capture files.