Main » 2011 November 23 » HOW TO CRACK WIFI/WIRELESS WPA/WPA2 ENCRYPTION
10:52 PM HOW TO CRACK WIFI/WIRELESS WPA/WPA2 ENCRYPTION | |
 You might have heard/learnt from me/others How to Crack Passwords of WEP but now i am going to tell you how to crack WPA/WPA2 Passwords. 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. he best document describing WPA is Wi-Fi Security - WEP,WPA and WPA2. This is the link to download the PDF directly. The WPA. 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 againstWPA/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. Use the injection test to confirm your card can inject. 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 can confirm that you can communicate with the specific AP by following these instructions. You are using v0.9.1 or above of aircrack-ng. If you use a different version then some of the command 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. Equipment used To follow this tutorial at home, you must have two wireless cards. In this tutorial, here is what was used: 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. These steps are mostly specific to the madwifi-ng driver - for other drivers, this procedure varies. (Most commonly, running the command "airmon-ng start First stop ath0 by entering: The system responds: 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: 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: To confirm the interface is properly setup, enter "iwconfig”. The system will respond: 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: Where: Here what it looks like if a wireless client is connected to the network: Here it is with no connected wireless clients: 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. 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. 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: Where: 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: Where: Here is typical output when there are no handshakes found: 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: 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: 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 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 amount may cause the client to fail to reconnect and thus does 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. Review your captured data using the WPA Packet Capture Explained tutorial to see if you can identify the problem. Such as missing AP packets, missing client packets, etc. Unfortunately, you sometimes 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 acknowledgements are capture. 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 "acknowledgement” 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 | |
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