You already know that if you want to lock down your Wi-Fi network, you
should opt for WPA encryption because WEP is easy to crack. But did you
know how easy? Take a look.
Note: This post demonstrates how to crack WEP passwords, an older and
less often used network security protocol. If the network you want to
crack is using the more popular WPA encryption, see our guide to
cracking a Wi-Fi network's WPA password with Reaver instead.
Today we're going to run down, step-by-step, how to crack a Wi-Fi
network with WEP security turned on. But first, a word: Knowledge is
power, but power doesn't mean you should be a jerk, or do anything
illegal. Knowing how to pick a lock doesn't make you a thief. Consider
this post educational, or a proof-of-concept intellectual exercise.
Dozens of tutorials on how to crack WEP are already all over the
internet using this method. Seriously—Google it. This ain't what you'd
call "news." But what is surprising is that someone like me, with
minimal networking experience, can get this done with free software and a
cheap Wi-Fi adapter. Here's how it goes.
What You'll Need
Unless
you're a computer security and networking ninja, chances are you don't
have all the tools on hand to get this job done. Here's what you'll
need:
- A compatible wireless adapter—This
is the biggest requirement. You'll need a wireless adapter that's
capable of packet injection, and chances are the one in your computer is
not. After consulting with my friendly neighborhood security expert, I
purchased an Alfa AWUS050NH USB adapter, pictured here, and it set me
back about $50 on Amazon. Update: Don't do what I did. Get the Alfa AWUS036H, not the US050NH, instead.
- A BackTrack Live CD. Download yourself a copy of the CD and burn it, or load it up in VMware to get started.
- A nearby WEP-enabled Wi-Fi network. The
signal should be strong and ideally people are using it, connecting and
disconnecting their devices from it. The more use it gets while you
collect the data you need to run your crack, the better your chances of
success.
- Patience with the command line. This
is an ten-step process that requires typing in long, arcane commands
and waiting around for your Wi-Fi card to collect data in order to crack
the password. Like the doctor said to the short person, be a little
patient.
Crack That WEP
To crack WEP, you'll need to launch Konsole, BackTrack's built-in
command line. It's right there on the taskbar in the lower left corner,
second button to the right. Now, the commands.
First run the following to get a list of your network interfaces:
airmon-ng
The only one I've got there is labeled ra0.
Yours may be different; take note of the label and write it down. From
here on in, substitute it in everywhere a command includes (interface).
Now, run the following four commands. See the output that I got for them in the screenshot below.
airmon-ng stop (interface)
ifconfig (interface) down
macchanger --mac 00:11:22:33:44:55 (interface)
airmon-ng start (interface)
If
you don't get the same results from these commands as pictured here,
most likely your network adapter won't work with this particular crack.
If you do, you've successfully "faked" a new MAC address on your network
interface, 00:11:22:33:44:55.
Now it's time to pick your network. Run:
airodump-ng (interface)
To see a list of wireless networks around you. When you see the one you
want, hit Ctrl+C to stop the list. Highlight the row pertaining to the
network of interest, and take note of two things: its BSSID and its
channel (in the column labeled CH), as pictured below. Obviously the
network you want to crack should have WEP encryption (in the ENC)
column, not WPA or anything else.
Like
I said, hit Ctrl+C to stop this listing. (I had to do this once or
twice to find the network I was looking for.) Once you've got it,
highlight the BSSID and copy it to your clipboard for reuse in the
upcoming commands.
Now we're going to watch what's going on with that network you chose and capture that information to a file. Run:
airodump-ng -c (channel) -w (file name) --bssid (bssid) (interface)
Where (channel) is your network's channel, and (bssid) is the BSSID you
just copied to clipboard. You can use the Shift+Insert key combination
to paste it into the command. Enter anything descriptive for (file
name). I chose "yoyo," which is the network's name I'm cracking.
You'll get output like what's in the window in the background pictured
below. Leave that one be. Open a new Konsole window in the foreground,
and enter this command:
aireplay-ng -1 0 -a (bssid) -h 00:11:22:33:44:55 -e (essid) (interface)
Here the ESSID is the access point's SSID name, which in my case is yoyo. What you want to get after this command is the reassuring "Association successful" message with that smiley face.
You're almost there. Now it's time for:
aireplay-ng -3 -b (bssid) -h 00:11:22:33:44:55 (interface)
Here we're creating router traffic to capture more throughput faster to
speed up our crack. After a few minutes, that front window will start
going crazy with read/write packets. (Also, I was unable to surf the web
with the yoyo network
on a separate computer while this was going on.) Here's the part where
you might have to grab yourself a cup of coffee or take a walk.
Basically you want to wait until enough data has been collected to run
your crack. Watch the number in the "#Data" column—you want it to go
above 10,000. (Pictured below it's only at 854.)
Depending on the power of your network (mine is inexplicably low at -32 in that screenshot, even though the yoyo AP
was in the same room as my adapter), this process could take some time.
Wait until that #Data goes over 10k, though—because the crack won't
work if it doesn't. In fact, you may need more than 10k, though that
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.
