Here is the how to:
Using the Aircrack-ng Suite
You should always start by confirming that your wireless card can inject
packets. This can be done by using the injection test.
Then start by following the Simple WEP Crack Tutorial.
Once you have mastered that technique, you can follow the other tutorials to
learn aircrack-ng in more detail.
Tutorial:
Simple sniffing and cracking
Discovering Networks
The first thing to do is looking out for a potential target. The aircrack-ng
suite contains airodump-ng for this - but other programs like Kismet can be
used too.
Prior to looking for networks, you must put your wireless card into what is
called “monitor mode”. Monitor mode is a special mode that allows your PC to
listen to every wireless packet. This monitor mode also allows you to
optionally inject packets into a network. Injection will be covered later in
this tutorial.
To put your wireless card into monitor mode:
airmon-ng start rausb0
To confirm it is in monitor mode, run “iwconfig” and confirm the mode. The
airmon-ng page on the Wiki has generic information and how to start it for
other drivers.
Then, start airodump-ng to look out for networks:
airodump-ng rausb0
“rausb0” is the network interface (nic) name. If you are using a different
WLAN device than a rt2570 you'll have to use a different nic name. Take a look
in the documentation of the nic driver. For most newer drivers, the primary
interface name is “wlan0”, but for monitoring, a secondary interface (“mon0”,
created when you run airmon-ng) is used.
If airodump-ng could connect to the WLAN device, you'll see a screen like
this:
airodump-ng hops from channel to channel and shows all access points it can
receive beacons from. Channels 1 to 14 are used for 802.11b and g (in US, they
only are allowed to use 1 to 11; 1 to 13 in Europe with some special cases;
1-14 in Japan). Channels between 36 and 149 are used for 802.11a. The current
channel is shown in the top left corner.
After a short time some APs and (hopefully) some associated clients will show
up.
The upper data block shows the access points found:
BSSID The MAC address of the AP
PWR Signal strength. Some drivers don't report it
Beacons Number of beacon frames received. If you don't have a signal
strength you can estimate it by the number of beacons: the more beacons, the
better the signal quality
Data Number of data frames received
CH Channel the AP is operating on
MB Speed or AP Mode. 11 is pure 802.11b, 54 pure 802.11g. Values between
are
a mixture
ENC Encryption: OPN: no encryption, WEP: WEP encryption, WPA: WPA or WPA2
encryption, WEP?: WEP or WPA (don't know yet)
ESSID The network name. Sometimes hidden
The lower data block shows the clients found:
BSSID The MAC of the AP this client is associated to
STATION The MAC of the client itself
PWR Signal strength. Some drivers don't report it
Packets Number of data frames recieved
Probes Network names (ESSIDs) this client has probed
Now you should look out for a target network. It should have a client
connected because cracking networks without a client is an advanced topic (See
How to crack wep with no clients). It should use WEP encryption and have a
high signal strength. Maybe you can re-position your antenna to get a better
signal. Often a few centimeters make a big difference in signal strength.
In the example above the net 00:01:02:03:04:05 would be the only possible
target because it's the only one with an associated client. But it also has a
high signal strength so it's really a good target to practice.
Sniffing IVs
Because of the channel hopping you won't capture all packets from your target
net. So we want to listen just on one channel and additionally write all data
to disk to be able to use it for cracking:
airodump-ng -c 11 --bssid 00:01:02:03:04:05 -w dump rausb0
With the -c parameter you tune to a channel and the parameter after -w is the
prefix to the network dumps written to disk. The ”--bssid” combined with the
AP MAC address limits the capture to the one AP. The ”--bssid” option is only
available on new versions of airodump-ng.
Before being able to crack WEP you'll usually need between 40 000 and 85 000
different Initialization Vectors (IVs). Every data packet contains an IV. IVs
can be re-used, so the number of different IVs is usually a bit lower than the
number of data packets captured.
So you'll have to wait and capture 40K to 85K of data packets (IVs). If the
network is not busy it will take a very long time. Often you can speed it up a
lot by using an active attack (=packet replay). See the next chapter.
Cracking
If you've got enough IVs captured in one or more file, you can try to crack
the WEP key:
aircrack-ng -b 00:01:02:03:04:05 dump-01.cap
The MAC after the -b option is the BSSID of the target and dump-01.cap the
file containing the captured packets. You can use multiple files, just add all
their names or you can use a wildcard such as dump*.cap.
For more information about aircrack-ng parameters, description of the output
and usage see the manual.
The number of IVs you need to crack a key is not fixed. This is because some
IVs are weaker and leak more information about the key than others. Usually
these weak IVs are randomly mixed in between the stonger ones. So if you are
lucky, you can crack a key with only 20 000 IVs. But often this it not enough
and aircrack-ng will run a long time (up to a week or even longer with a high
fudge factor) and then tell you the key could not be cracked. If you have more
IVs cracking can be done a lot faster and is usually done in a few minutes, or
even seconds. Experience shows that 40 000 to 85 000 IVs is usually enough for
cracking.
There are some more advanced APs out there that use an algorithm to filter out
weak IVs. The result is either that you can't get more than “n” different IVs
from the AP or that you'll need millions (like 5 to 7 million) to crack the
key. Search in the Forum, there are some threads about cases like this and
what to do.
Active attacks
Injection support
Most devices don't support injection - at least not without patched drivers.
Some only support certain attacks. Take a look at the compatibility page,
column aireplay. Sometimes this table is not up-to-date, so if you see a “NO”
for your driver there don't give up yet, but look at the driver homepage, the
driver mailing list or our Forum. If you were able to successfully replay
using a driver which is not listed as supported, don't hesitate to update the
compatibility page table and add a link to a short howto. (To do this, request
a wiki account on IRC.)
The first step is to make sure packet injection really works with your card
and driver. The easiest way to test it is the injection test attack. Make sure
to perform this test prior to proceeding. Your card must be able to
successfully inject in order to perform the following steps.
You'll need the BSSID (AP MAC) and ESSID (network name) of an AP that does not
do MAC filtering (e.g. your own) and must be in range of the AP.
Try to connect to your AP using aireplay-ng:
aireplay-ng --fakeauth 0 -e "your network ESSID" -a 00:01:02:03:04:05 rausb0
The value after -a is the BSSID of your AP.
If injection works you should see something like this:
12:14:06 Sending Authentication Request
12:14:06 Authentication successful
12:14:06 Sending Association Request
12:14:07 Association successful :-)
If not
1.
double-check ESSID and BSSID
2.
make sure your AP has MAC filtering disabled
3.
test it against another AP
4.
make sure your driver is properly patched and supported
5.
Instead of “0”, try “6000 -o 1 -q 10”
ARP replay
Now that we know that packet injection works, we can do something to massively
speed up capturing IVs: ARP-request reinjection
The idea
ARP works (simplified) by broadcasting a query for an IP and the device that
has this IP sends back an answer. Because WEP does not protect against replay,
you can sniff a packet, send it out again and again and it is still valid. So
you just have to capture and replay an ARP-request targeted at the AP to
create lots of traffic (and sniff IVs).
The lazy way
First open a window with an airodump-ng sniffing for traffic (see above).
aireplay-ng and airodump-ng can run together. Wait for a client to show up on
the target network. Then start the attack:
aireplay-ng --arpreplay -b 00:01:02:03:04:05 -h 00:04:05:06:07:08 rausb0
-b specifies the target BSSID, -h the MAC of the connected client.
Now you have to wait for an ARP packet to arrive. Usually you'll have to wait
for a few minutes (or look at the next chapter).
If you were successful, you'll see something like this:
Saving ARP requests in replay_arp-0627-121526.cap
You must also start airodump to capture replies.
Read 2493 packets (got 1 ARP requests), sent 1305 packets...
If you have to stop replaying, you don't have to wait for the next ARP packet
to show up, but you can re-use the previously captured packet(s) with the -r
<filename> option.
When using the arp injection technique, you can use the PTW method to crack
the WEP key. This dramatically reduces the number of data packets you need and
also the time needed. You must capture the full packet in airodump-ng, meaning
do not use the ”--ivs” option when starting it. For aircrack-ng, use “aircrack
-z <file name>”. (PTW is the default attack in 1.0-rc1.)
If the number of data packets received by airodump-ng sometimes stops
increasing you maybe have to reduce the replay-rate. You do this with the -x
<packets per second> option. I usually start out with 50 and reduce until
packets are received continuously again. Better positioning of your antenna
usually also helps.
The aggressive way
Most operating systems clear the ARP cache on disconnection. If they want to
send the next packet after reconnection (or just use DHCP), they have to send
out ARP requests. So the idea is to disconnect a client and force it to
reconnect to capture an ARP-request. A side-effect is that you can sniff the
ESSID and possibly a keystream during reconnection too. This comes in handy if
the ESSID of your target is hidden, or if it uses shared-key authentication.
Keep your airodump-ng and aireplay-ng running. Open another window and run a
deauthentication attack:
aireplay-ng --deauth 5 -a 00:01:02:03:04:05 -c 00:04:05:06:07:08 rausb0
-a is the BSSID of the AP, -c the MAC of the targeted client.
Wait a few seconds and your arp replay should start running.
Most clients try to reconnect automatically. But the risk that someone
recognizes this attack or at least attention is drawn to the stuff happening
on the WLAN is higher than with other attacks.
If you need more information, just ask, I will answer, but tomorrow, it's bed
time for me.
Thierry
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