Isnin, 12 November 2007

by: George Ou

Even after two years of WPA certification and nearly one year after 802.11i ratification, you might be wondering why I’m still talking about WEP encryption. The fact is, I would love to stop talking about it if there weren’t such an overwhelming percentage of corporations, retail outlets, and hospitals still using WEP. Although WPA brought us TKIP (think of TKIP as WEP 2.0) encryption and 802.11i brought us AES encryption, the upgrade process has been extremely painful and many products still don’t support TKIP let alone AES. The sad state of wireless LAN security is that the majority of corporations and hospitals still use dynamic per-user, per-session WEP keys while the majority of retail outlets that I’ve seen still use a single, fixed WEP key.

In the past, a hacker was at the mercy of waiting long periods of time for legitimate traffic on a wireless LAN to collect 10 million of packets to break a WEP key. In my previous blog on this topic, which was based on Mike Ossmann’s WEP article, I alerted you to the startling fact that even wireless LANs that used 802.1x/EAP authentication to dynamically assign unique per-user, per-session WEP keys were no longer safe against WEP hacking since WEP cryptanalysis had improved 50 fold. Instead of waiting for hours or even days for those 10 million packets, you now only needed about 200,000 packets to break WEP. Even though dynamic WEP key rotation could change a user’s WEP key every few minutes or so (note that key rotation isn’t always implemented by default), the new WEP cryptanalysis techniques put even dynamic WEP in striking range. Now with the new active attacks on WEP described in Ossmann’s follow-up article, hackers no longer need to passively wait for legitimate packets on a wireless LAN because they can actively inject packets into a wireless LAN to ensure a speedy packet collection session. The end result is, any WEP based network with or without Dynamic WEP keys can now be cracked in minutes! If you’re scared, you should be and you’d better go back and read the recommendations in the end of my previous blog if you’re still running WEP in any form.