Learn Ethical Hacking Episode #30: Aircrack-ng and Crunch Usage Example (Part 1)


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Hello everybody and welcome to this tutorial. Today, we will cover how to crack Wi-Fi. Now that we have finished setting up all of the necessary tools, we can begin with the demonstration.

The first thing that we will need to do is set our network wireless card in to monitor mode. Type in ifconfig, press Enter, and this will display all of the network interfaces that are available. My wireless interface is called wlp2s0. A bit of a strange name, I know, but Fedora has a custom of assigning strange names. For example, my wired connection is called p8p1, which is kind of weird, but OK, never mind. Just identify the name of your interface and adapt accordingly. Anyway, I’m going to use wlp2s0. We have two ways of configuring monitor mode. The first method is what I usually use to set it in monitor mode, and the second one is what I use to check for problems. Go ahead and type in ifconfig. Again, wlp2s0, which is the name of my wireless network card, and type in down. Let’s shut our wireless card down completely. Now we can make some modifications to it. Type in ipconfig wlp2s0, mode monitor. Again, ifconfig wlp2s0 up, and now our network card is configured to function in monitor mode. Before it was functioning in the promiscuous mode. There are several names for it, but promiscuous mode is the most common. The difference between the two modes is that in monitor mode network cards are configured to accept packages, regardless if it is meant for them or not, and in promiscuous mode they will only accept packages that are meant specifically for them.

I’m going to go ahead and clear the screen, and I’m finally going to start using some of the software packages that come with aircrack. I have a list of commands here which we will use today on the right side of my screen, and we’re going to use a few other ones, but these are the basic ones that you absolutely need to know. So, let me go ahead and type in airmon-ng check wlp2s0. I want to see if there are any possible processes that could cause interference, and I see that there are quite a few of them. One of the first things that you need to kill is the network manager. Even though it doesn’t actually directly interfere with the functioning of our software, it does spawn some other processes that might interfere, like your active internet connection here, the dhclient. For example, if your network manager is configured to automatically connect to a certain network, or to a wired network that you plug into your computer. So, let’s just go ahead and kill the process. I’m not going to take any chances, today. I’m going to go ahead and kill the network manager, and then I will begin killing the rest. So, let’s repeat the airmon-ng check, excellent! I have a few more of these. You will need to kill them in a certain order because they tend to spawn each other. Even though you’ve killed it as root, it will kill it, but it will restart it as well. I’ll just go ahead and kill the dhclient as well in order to prevent any interference, and the rest of killing can be done in any way you like. So, kill, let’s just go ahead and kill 1556, 1215, and 1216. Excellent! Let’s do a check one more time, something is still up. This is what I meant, it is highly annoying. Avahi-demons are the only ones running. Apparently, I have to kill the WPA supplicant first, and then I can kill these. It can be frustrating because you can’t kill them all at once. You will have to type in the commands time and time again. Let me just go ahead and clear the screen, and always perform an extra check. You see here that nothing is active, nothing should present any problems now.

Let me go ahead and clear the screen. The next thing that we need to do is perform a scan of our environment here to see what sort of networks are available, and who is connected to which networks. Now you cannot see with the network manager. With the network manager we can only see the visible wireless access points around us. While on the other hand, with one of the tools that comes with the aircrack, you can actually see wireless access points around you and who is connected to them, which is a very nice feature. I’ll go ahead and type in the first command from my selected list here, it’s airodump-ng wlp2s0, and press Enter. You can now see all of the wireless access points. This one is mine, it’s called Something. I’ve created this network specifically for the purposes for this tutorial. It has a good, strong password, and we are going to be cracking it today. Okay, let me cancel the scanning process, and I would like to explain a few of the things that you can see here during the scanning process itself. The BSSID is the MAC address of the wireless access point. The PWR is the strength of the signal. So, the smaller this negative number is, so let’s say -30, -15 is a stronger signal than -30. -57 will not be the greatest of connections. -78 or -84, yeah, you might be able to connect to them, but this will certainly result in a poor connection. However, even though the signals here are weak, if you have a good enough wireless card you will be able to perform the authentication, and therefore I will be able to render any of these networks that you see here inoperable. But, that we will save for the later tutorials.

For the time being, I would like to show you one of the ways in which you can crack the WPA2 encryption. DoS attacks are very useful. I mean, they can practically render almost any WiFi network out there useless. Nobody will be able to connect to it, or you can deauthenticate a specific client on the network which is also extremely useful. So, let’s go ahead and clear the screen. Once again, I will run airodump, and I will expand this terminal window so we can see some other things as well. It says something, it’s 90:F6. I am looking for something to be associated with 90:F6, and that is what I shall use in order to actually deauthenticate, because we are looking for a four-way handshake. It will appear in the top right corner. There we will be able to see all of the packets that are coming in, and there we will be able to actually capture a file and see what is going on. However, that is not possible to do at the time being because we are scanning for pretty much every single network available, and I just wanted to show you what it looks like.

The next thing that we need to do is perform a targeted scan. We will be targeting this network here, as it has a good signal. More importantly than that, I have permission to do whatever I want with this network, as it is mine. These down below are not mine. Also, keep in mind that we are not doing anything illegal here. Everything that you see here is public information. This is simply what all of the Wi-Fi routers around me are broadcasting. They are broadcasting their MAC address, and they are are broadcasting the name of the network, basically. The SSID name is not a technical term. ESSID is the term, but everybody refers to it as the name of a wireless access point. Anyway, as I said, all of this is public information. You will see that it’s WPA2 encryption, you will see the MAC address, and you will see the ESSID. The ESSID will be the first thing that you see on the network. Also, you will see the channels as well. Anyway, I will call the tutorial here, and in the next one we will be performing a specific scan where we will capture information, and use that capture file in order to crack the encryption. Until then I bid you farewell, and I hope to see you in the next tutorial.

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