Because Wi-Fi is a broadcast technology that passes through the open air anyone with the right equipment can pick up the signal, for this reason it is very important that these signals are encrypted to avoid information being intercepted by the wrong people. One of the most common ways of encrypting a Wi-Fi network is by using a technology called WPA2 – Wi-Fi Protected Access.
WPA2 is commonly set-up with a Pre-Shared Key (PSK), this alphanumeric string should only be known by those who need access to the network and they enter the key when they are connecting to the network. The potential problem with this approach is that the PSK is used to generate the encryption key and if you use a weak key then the network is left open to a fairly simple attack which can gain access to the network within minutes.
The solution is simple – longer and more complex keys! For every character added the cracking process becomes considerably harder by a factor of compute years. The question is how long. There is no agreed answer on this as it depends on how random the key is. A truly random key of 10 alphanumeric characters is actually very hard to break, taking many years but a similar length key using dictionary words could be broken very quickly.
To be safe we normally recommend a minimum of 12 characters with typical password rules – upper and lower case, numeric characters, special characters and no dictionary words unless they have character replacements.
Of course a strong key only remains strong whilst it is only known by those who should know it and this is a weakness of the shared key approach as if the key is leaked, security across the network is compromised. There are additional factors that can be introduced to improve security further – for example one technique is called Dynamic Pre-Shared Key (D-PSK) which uses dynamic, unique keys for each user so there is no risk of a leaked key. Other more advanced set-ups use electronic certificates rather than passwords. With the right set-up Wi-Fi networks are perfectly secure – more so than most wired networks!