How to Hack a WPA Wireless Network (Wifi) using Aircrack-ng and John the Ripper

Here is a video tutorial I created showing how easy it is to hack a wireless network using WPA keys for their security. It's a short 12 minute video and I hope you find it not only instructional, but also liberating. After all, informed people make the best decisions.

John the Ripper (JtR) cracks passwords offline. That is, "incorrect number of passwords entered limit" does not affect  JtR. As you can see in the video, using aireplay-ng, fake deauthentication packets were injected to the wireless access point  to force all users to reauthenticate (without them knowing it). During reauthentication, the WPA keys are exchanged between the client and the wireless access point. This exchange was recorded into a file "wificrack.cap" and the hashed PSK (Pre-Shared Key) was then cracked using JtR.  In the video, you can also see that the output file of airodump-ng can be opened using Wireshark. Opening the cap file with Wireshark reveals a lot of information about the clients connected to the wireless access point. For instance, we know the wireless AP is a Cisco-Li (Cisco-Linksys), and the WPA handshake captured was from an Apple device. The MAC address is even shown!

Freeing Disk Space in Kali Linux (Basic steps), Especially the apt-get Cache

Kali is a Debian-based Linux developed with penetration-testers in mind. Think of it as a toolbox. It is basically a Debian Linux, but with all the penetration testing tools installed, for free. This includes Metasploit, OpenVAS vulnerability scanners, exploitDB, Hydra, aircrack-ng, John the Ripper, etc. These come on top Linux's common formidable tools such as OpenSSH (for creating tunnels), netcat, and nmap to name a few. 

Since Kali is Debian, then the method used here do apply to any Debian-based Linux systems (+ Ubuntu). Although, since we are talking about Kali, which is usually ran as 'root', then most of the screenshots will show that the user is running the commands as root. If you are not logged in as root, just add the word 'sudo' in the beginning of every command. For example: instead of issueing command 'apt-get clean', type 'sudo apt-get clean'.

Let us assume, you get an error in your Kali Linux saying that you are running out of space. In the screenshot below, My Kali is running on Oracle VirtualBox with a dynamically allocated 15Gb of space. Technically I don't have to worry about disk space because the Virtual Disk will expand when needed. But I still want to free some space.  

You get an error that you are running on disk space. Kali

Step 1: Check Disk space and where you are consuming space the most. Use df -h. the '-h' option in df is to format the result in 'human-readable' format. 

df -h results show the entire disk is "full"

How to configure TFTP Server in your Linux Machine (Debian), and how to solve Permission Denied Error (Error Code 2)

I personally use a Virtualized Kali Linux in my Windows 7 machine to do a lot of things. Primarily to do IT security analysis and research for the companies I work with. But mostly, I find maintaining a Linux machine in an image comes in handy for a lot of things: I can use the Kali/Linux machine as an tftp/scp server to backup devices;

So suppose you want to copy startup-config files from your Cisco to your laptop running a virtual machine of  Kali Linux, (Debian). Let us suppose further that your Cisco router/switch cannot do SSH otherwise, we'll just use scp which is safer, and does not need any further special configuration for Linux devices.

Here's how to do it:  

1. Make sure you have the Virtual Machine in Bridged Adapter to your WIndows 7 machine's ethernet adapter. I'm using virtual box so in my case, I have to create a bridged adapter first. In Virtuabox (not in the Guest OS or Virtual Machine's Window) click File >> preferences >> Network. Then under tha tabe Bridged Adapters, create at least one adapter. 
             

           Then , in your Guest / Virtual Machine, click Machine >> Settings >> Network >> choose bridged (not NAT). After which, you need to do an ifdown eth0 and ifup eth0 inside your Kali / Linux OS console.

** Bridging will not work when you hav eport-security configured in the switchport where the computer is plugged. This is the case in most enterprise networks. If you are doing this inside your office and you are not getting a DHCP IP address, you better ask your network engineer/corporate IT if port-security is enabled.