How hackers crack WiFi passwords.

WiFi is one of, if not the most common wireless technology. Its security is important not only in enterprise networks but in our everyday life.

Today i'll cover how attackers crack WiFi networks with WPA2 encryption, which corresponds to nearly 75% of today's networks.

First we need to talk about what we are cracking.

4-way handshake

We can see 4 EAPOL (Extensible Authentication Protocol over LAN) packets with a lot of new keywords, lets go over them one by one.

ANonce - access point nonce - a random number generated by the access point.

SNonce - station nonce - a random number generated by the client.

Both of these are here to ensure that encryption is different between sessions.

PTK (Pairwise Transient Key) = PRF (PMK + ANonce + SNonce + Mac (AP)+ Mac (Client))

PMK (Pairwise Master Key) = PBKDF2 (Passphrase, SSID, 4096)

Here both PRF and PBKDF2 are cryptographic functions used to derive the values of PMK and PTK, the third value in PBKDF2, represents the number of hashing iterations done by the function, for WPA2 its 4096.

PTK is later used for encrypting the session.

MIC (Message Integrity Code) - Ensures that both the client and the ap get the same keys for successful encryption.

GTK (Group Temporal Key) - is a unique key shared by all the devices on the network, it's used to encrypt Broadcast and Multicast traffic.

The last ACK message informs the AP that the client derived an installed all encryption keys successfully and that the client will use encryption from now on.

*Even tho this might seam complicated but it's a big simplification of the 4-way handshake. Full inner workings of this process are outside of scope of this article.

From the explanation above you probably deduced that a hacker would be most interested in the PMK value. If it is known, you could brute-force the passphrase. This is where the hacking part comes in.

Aircrack-ng

!!!SECTION BELOW IS PURELY EDUCATIONAL, AND DONE IN A CONTROLLED ENVIRONMENT, DO NOT ATTACK NETWORKS WITHOUT PERMISSION OF ITS OWNER!!!

Aircrack-ng is a network software suite consisting of a detector, packet sniffer, WEP and WPA/WPA2-PSK cracker and analysis tool for 802.11 wireless LANs.

We will need a network adapter that supports both monitor and packet injection modes.

First we will use airmon-ng to put our adapter in monitor mode:

Now that my adapter is in monitor mode i can begin sniffing, using airodump-ng:

I have to snip out a lot of my neighbors networks, but we will focus on my home-lab one with SSID of: dd-wrt. Right now airodump is jumping around channels to find all available networks. The network im attacking is on channel 2, we can listen to only that channel, also we can listen for packets only related to the victim network:

We can see a station with a mac address of: D6:73:AF:3D:D7:F2 - aka. my phone. In theory that's all we have to do to capture a handshake. we can specify -w flag with a filename so when we capture a handshake it will get saved into a file. But still we would need to wait for a device to authenticate, or we could force it to do so.

Deauthentication packets

Deauthentication packets are normally defined in the WiFi standard. Normally they are used to terminate a WiFi connection for a number of reasons. Problem with modern devices is that when they are deauthenticated/they loose connection, they will immediately try to reconnect, or in our case reauthenticate.

While listening with airodump, we can use aireplay-ng to deauthenticate my phone off the network:

Now we can see that in the top right corner of airodump (that was running in the background) appeared "WPA handshake: 00:21:91:32:8B:1F", and also next to our client we can see a not saying EAPOL. That's how we know we captured a handshake, now lets crack it.

Cracking the capture

First we will need to get the hash out of the capture file we got above, we can do that by using hcxpcapngtool from hcxtools package:

Now we got a file called hash with all we need to crack the password. Note that this file doesn't really contain just a hash, it contains versions, mac addresses, SSID and other captured data required to crack the password.

Now lets use hashcat to finally get the password, I'll use a dictionary attack with well know rockyou.txt wordlist. To do that I will specify attack mode to straight with -a 0 flag and set the hash mode with -m 22000.

We can see the password: spiderman080403

It took seconds on a GTX 1060 6GB, just imagine what a top shelf graphics card could do while brute-forcing. And the questions is:

How to protect yourself?

First of all use a unique, long, complicated password, never the default one that comes in with your router. If you can start using WPA3 do it, if you have devices that don't support it, maybe try to put them on a separate network, that will be less secure because of WPA2.

Now try replicating the steps shown in this article, also try securing your home network.