Wireless forensics is the process of capturing information that moves over a wireless network and trying to make sense of it in some kind of forensics capacity.
Wireless Local Area Networks
WLANs are standardized under the IEEE 802.11 series.
Common encryption technologies used by these networks are: WEP, WPA/WPA2-PSK, some networks have no encryption at all.
In order to decrypt intercepted secured WLAN traffic you should crack the encryption key. Note, that the only option for cracking WPA/WPA2-PSK keys is to do a brute-force password guessing attack. There are several WPA-PSK rainbow tables available.
Many commercial network forensics systems can intercept and decrypt WLAN traffic, for example:
As well as some open-source tools: