Handshaking can be done to decide which parameters are appropriate to systems and equipment at both ends of the transmission channel, including but not limited to hardware features, protocol features, interrupt procedure, parity, coding alphabet, information transfer rate, and so forth.
Whenever a computer interacts with another machine such as a network server, printer, or modem, it requires a handshake in order to make the establishment of a connection possible—no exceptions.
Handshakes enable people to connect relatively different, varied, and non-homogenous equipment or systems over a transmission channel without setting parameters manually or requiring the need for human (preferably tech-savvy technicians) intervention.
With that said, it's quite common for hackers to attempt using the handshake itself as a means to intercept, infiltrate, and otherwise steal a connection.
In fact, one of the most exploitable and arguably useless security protocols ever created—WEP—was commonly abused this way. Thankfully, thanks to the sheer complexity of the WPA2 or Wired Protected Access 2, exploiting handshakes is easier said than done.
Even though it requires handshakes to operate just like any other network protocol, it is the most cutting-edge encryption protocol to beat at this time.
Nevertheless, there are a myriad of methods available to crack open the present WPA2 standard that specifically targets the WPA2 handshake.
After all, the handshake is the point where your computer is most vulnerable to hacker attacks and cracks even if it is done with WPA2 encryption. It's also the very thing you want to capture if you're a hacker who wants to infiltrate a WPA2-encrypted connection.
Granted, basic password and key creation guidelines is all it takes to stop WPA2 from getting cracked, handshake or no handshake (for example, making the password as long as possible or using alphanumeric password characters).
The fact of the matter is that whenever you're attempting a connection between your computer and a network server, handshakes will happen in order for it to work, so that's the very first thing hackers will target and the first thing security experts will try to protect from getting exploited.
More to the point, capturing the full-authentication handshake from the access point is the backdoor you need to gain entry into the WiFi network of your choice and leech off some free Internet access.