How to Crack a Wi-Fi Network’s WEP Password with BackTrack
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. The guy in this video
below is using a $12 model he bought on Ebay (and is even selling his router of
choice). There are plenty of
resources on getting aircrack-compatible adapters out there.
- A BackTrack Live CD. We
already took you on a full
screenshot tour of how to install and use BackTrack 3, the Linux Live
CD that lets you do all sorts of security testing and tasks. 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:
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.
Tech
site Ars Technica runs down the basics of securing your home wireless
network with the most secure and up-to-date methods. The main takeaway
is that when you enable encryption on your wireless router, use WPA
encryption instead of WEP, because it's better and stronger.
