Mathy gave an excellent talk showing ways to attack wireless security (WPA2) via a group key used for broadcast transmissions. This leads to decryption of all traffic. It included introductions to all the relevant parts of the system and a demo.
The take-away message is actually rather short:
People standardize and implement bad RNGs and if those are used to generate cryptographic secrets it leads to vulnerabilites.
It included a few more tricks and gimmicks and I recommend you watch the Video.