How to Crack a Wi-Fi Network’s WEP Password with BackTrack

t seems to be a working threshold for many.

Once you've collected enough data, it's the moment of truth. Launch a third Konsole window and run the following to crack that data you've collected:

aircrack-ng -b (bssid) (file name-01.cap)

Here the filename should be whatever you entered above for (file name). You can browse to your Home directory to see it; it's the one with .cap as the extension.

If you didn't get enough data, aircrack will fail and tell you to try again with more. If it succeeds, it will look like this:

Full size

The WEP key appears next to "KEY FOUND." Drop the colons and enter it to log onto the network.

Problems Along the Way

With this article I set out to prove that cracking WEP is a relatively "easy" process for someone determined and willing to get the hardware and software going. I still think that's true, but unlike the guy in the video below, I had several difficulties along the way. In fact, you'll notice that the last screenshot up there doesn't look like the others—it's because it's not mine. Even though the AP which I was cracking was my own and in the same room as my Alfa, the power reading on the signal was always around -30, and so the data collection was very slow, and BackTrack would consistently crash before it was complete. After about half a dozen attempts (and trying BackTrack on both my Mac and PC, as a live CD and a virtual machine), I still haven't captured enough data for aircrack to decrypt the key.

So while this process is easy in theory, your mileage may vary depending on your hardware, proximity to the AP point, and the way the planets are aligned. Oh yeah, and if you're on deadline—Murphy's Law almost guarantees it won't work if you're on deadline.