Introduction
The security of our WiFi networks is something often taken for granted, yet it forms a crucial line of defense against unauthorized access to our personal data and resources. WPA and WPA2, once considered robust security protocols, are now susceptible to various attack methods. One such method, the dictionary attack, leverages a pre-compiled list of potential passwords to attempt to crack the network’s key. This article will guide you through the process of performing a dictionary attack on a WPA/WPA2 network using Aircrack-ng on the BackTrack 5 platform. We will explore capturing the essential handshake, setting up your environment, and launching the attack itself.
IMPORTANT: This tutorial is intended for educational purposes only. You should only attempt these techniques on networks that you own or have explicit permission to test. Unauthorized access to computer systems is illegal and unethical. This information is provided to help you understand the vulnerabilities of WPA/WPA2 and how to strengthen your own network security. Please be a responsible and ethical user of this knowledge.
This guide is tailored for individuals with a beginner to intermediate level of technical understanding, ideally with some previous experience navigating the Linux operating system. Let’s dive in.
Understanding the Tools and Concepts
Before we delve into the practical steps, it’s crucial to understand the tools and concepts we’ll be using.
Aircrack-ng The WiFi Security Toolkit
Aircrack-ng is not just a single program, but rather a suite of tools designed for assessing the security of WiFi networks. This powerful suite encompasses various functionalities, including packet sniffing, analyzing captured data, and, most importantly for our purposes, cracking WEP and WPA/WPA2 encryption. The tools within Aircrack-ng allow you to intercept network traffic, identify potential weaknesses, and attempt to exploit those weaknesses to gain unauthorized access. The suite includes tools such as airodump-ng for packet capture and aircrack-ng itself for password cracking.
BackTrack and the Rise of Kali Linux
BackTrack was a Linux distribution specifically built for penetration testing and digital forensics. It came pre-loaded with a vast array of security tools, including Aircrack-ng. However, BackTrack is now considered legacy. Its successor, Kali Linux, is the current standard for penetration testing. Kali Linux offers a more up-to-date collection of tools, a more stable environment, and ongoing support and updates. While we will be discussing this process in the context of BackTrack because many tutorials still reference it, you should ideally use Kali Linux for actual security testing. The fundamental principles and many of the commands remain the same, although some adjustments might be necessary. Aircrack-ng, in particular, functions almost identically between the two.
Dictionary Attacks Brute Force with a Head Start
A dictionary attack is a method of password cracking that involves trying a pre-defined list of potential passwords, often referred to as a dictionary or wordlist. These lists typically contain common passwords, words from dictionaries, names, and other frequently used combinations. The software cycles through this list, attempting each password against the target network until a match is found. The success of a dictionary attack hinges on the quality and comprehensiveness of the dictionary used. The larger and more diverse the dictionary, the higher the likelihood of cracking the password. However, dictionary attacks are limited by the content of the wordlist. If the target password is not present in the dictionary, the attack will fail. This is why more sophisticated methods like brute-force attacks (trying every possible combination) are sometimes necessary, although they are much more time-consuming.
The WPAPWA Handshake The Key to Cracking
The WPA/WPA2 handshake is a critical part of the authentication process between a wireless client and a router. It’s a four-way exchange of packets that establishes a secure connection. This handshake contains the information necessary to derive the network’s password. Therefore, capturing this handshake is essential for cracking the WPA/WPA2 encryption. Without the handshake, you cannot perform a dictionary attack. The handshake occurs when a client initially connects to the network or when it reconnects after being disconnected. We will use Aircrack-ng tools to force a client to reconnect, creating a new handshake to capture.
Setting up Your Environment
To begin, you need to ensure your environment is properly configured. We’ll focus on the procedures for BackTrack, but remember these are largely similar in Kali Linux.
Installing Aircrack-ng
While Aircrack-ng is usually pre-installed on BackTrack and Kali Linux, you might need to install it if it’s missing or outdated. Open a terminal window and use the following command:
apt-get update
apt-get install aircrack-ng
This command will update the package lists and then install the Aircrack-ng suite.
Enabling Monitor Mode
Your wireless adapter needs to be in monitor mode to capture network traffic. This mode allows the adapter to passively listen to all traffic on a channel, rather than just the traffic destined for it. Use the airmon-ng script to manage monitor mode. First, kill any processes that might interfere with monitor mode:
airmon-ng check kill
Then, start monitor mode on your wireless interface. The interface name is often wlan0, but it might be different on your system.
airmon-ng start wlan0
This command will create a new interface, typically named wlan0mon, which is your wireless adapter in monitor mode.
Capturing the WPAPWA Handshake
Now that your environment is set up, we can proceed with capturing the WPA/WPA2 handshake.
Identifying the Target Network
Use airodump-ng to scan for nearby wireless networks. This tool displays information about each network, including its BSSID (the router’s MAC address), ESSID (the network name), channel, and signal strength.
airodump-ng wlan0mon
Pay attention to the output and identify the target network that you have permission to test.
Focusing on the Target Network
Once you’ve identified the target network, use airodump-ng to focus on that specific network and channel. This will reduce the amount of data captured and make it easier to find the handshake.
airodump-ng -c <channel> --bssid <BSSID> -w <capture_file_prefix> wlan0mon
Replace <channel> with the channel number of the target network, <BSSID> with the BSSID of the target network, and <capture_file_prefix> with a prefix for the capture file (e.g., “mycapture”).
Deauthenticating a Client
To force a handshake, you can deauthenticate a client connected to the target network. This will cause the client to disconnect and reconnect, triggering a new handshake. Use aireplay-ng to send deauthentication packets.
aireplay-ng -0 1 -a <BSSID> -c <client_MAC_address> wlan0mon
Replace <BSSID> with the BSSID of the target network and <client_MAC_address> with the MAC address of a connected client. If you don’t know the client’s MAC address, you can try sending a deauthentication packet to the broadcast address (FF:FF:FF:FF:FF:FF), but this might not always work.
Watch the airodump-ng output for the message “WPA handshake: <BSSID>”. This indicates that the handshake has been captured.
Verify Handshake Capture
Before launching the dictionary attack, verify that the handshake was captured correctly. Use aircrack-ng with the verify option.
aircrack-ng -v <capture_file_prefix>.cap
If the handshake is valid, the output will confirm that. If it’s invalid, repeat the capture process.
Performing the Dictionary Attack
With the handshake captured, you can now perform the dictionary attack.
Choosing a Dictionary
The success of a dictionary attack depends heavily on the dictionary used. Popular wordlists include rockyou.txt (often found in Kali Linux) and other lists available online. Consider the likely characteristics of the target password when selecting a dictionary. A good dictionary should include common passwords, variations of words, names, and other potentially relevant terms.
Running Aircrack-ng with the Dictionary
Use the following command to run Aircrack-ng with the dictionary:
aircrack-ng -w <dictionary_file> <capture_file_prefix>.cap
Replace <dictionary_file> with the path to your dictionary file and <capture_file_prefix>.cap with the name of the capture file. Aircrack-ng will then begin trying passwords from the dictionary against the captured handshake.
Interpreting the Results
If Aircrack-ng finds the password, it will display it in the output. If it exhausts the dictionary without finding the password, it will indicate that the password was not found in the list.
Troubleshooting
Common errors include incorrect interface names, invalid handshake captures, and dictionary format issues. Double-check your commands and ensure that you have captured a valid handshake before starting the attack.
Security Considerations and Mitigation
Successfully cracking a WiFi password should highlight the importance of robust network security. Here are some ways to enhance your security:
Employ Strong Passwords
The most basic but effective defense is a strong, complex password. Aim for a password that is at least twelve characters long and includes a mix of uppercase and lowercase letters, numbers, and symbols.
Consider WPA
WPA3 is the latest WiFi security protocol and offers significant improvements over WPA2, including stronger encryption and authentication methods.
Change Passwords Periodically
Regularly changing your WiFi password is a good practice, especially if you suspect that your network has been compromised.
This tutorial has demonstrated how dictionary attacks work and how easily they can compromise poorly secured networks. Use this knowledge responsibly and prioritize securing your own networks. Remember, unauthorized access to computer systems is illegal. Focus on prevention and responsible use of these techniques for ethical security testing. Stay safe online!
