April 5th, 2007
German researchers put final nail in WEP
A group of German cryptographic researchers (Erik Tews, Andrei Pychkine, and Ralf-Philipp Weinmann) at the cryptography and computer algebra group at the technical university Darmstadt in Germany have come up with a new statistical attack against WEP (Wired Equivalent Privacy) that's faster than anything achieved before. Wireless security researcher Jon "Johnny Cache" Ellch was so impressed with the work that he declared, "This is going to be more than an order of magnitude faster than all of the previous statistical attacks." Ellch added that the code weighed in at an "astounding 700 lines of code" and that he couldn't wait to start testing and re-implementing it.
Up until this point, with the KoReK class of attacks being the fastest thing around, I've typically considered WEP 104 (incorrectly known as WEP 128) to be breakable in just over eight minutes on average on an 802.11g network operating at peak 24 mbps sustainable throughput. Under idle network conditions, a passive attack on WEP would be impractical, but an attacker can use ARP replay attacks to induce responses from legitimate hosts to generate data. Using the packet injection ARP replay attack, WEP 104-bit encryption would be broken in about 22 minutes on average.
But with the new aircrack-ptw (Pychkine Tews Weinmann) algorithm, which runs about 20 times faster than the previous class of WEP-cracking algorithms based on the work of hacker "KoReK," WEP can fall in an average of 20 seconds on an 802.11g network and an average of 80 seconds on an 802.11b network if the network is very busy. For an idle network that's being attacked with packet injection, WEP can fall in an average of 52 seconds for 802.11g or 3.5 minutes with 802.11b. But we have to assume the worst, and the cracking can sometimes happen even faster than the average times I listed. What this means is that WEP (even with dynamic key rotation) is officially broken beyond repair.
I had pretty much declared WEP dead more than two years ago, but there was some room left for aggressive dynamic WEP key rotation. Now that WPA and even WPA2 can be automatically deployed within the Windows environment, there really is no excuse to be using WEP anymore. As of this latest round of WEP-cracking with aircrack-ptw, I'm adding WEP to my list of wireless LAN myths as the seventh dumbest way to secure a wireless LAN. It's still at the bottom of the list because WEP at least still takes a little bit of work to crack, whereas it takes ZERO effort to crack MAC filtering, SSID hiding, and DHCP disabling.
Businesses can follow my ultimate enterprise wireless LAN security guide. Home users need to implement WPA-PSK with a simple random 10-character (or more) alphanumeric password. For those of you who own a Nintendo DS system, you may be tempted to downgrade your security to WEP to accommodate your WPA-incapable Nintendo DS. But you've been warned how dangerous it is to run WEP. When the Sony PSP came out with WEP-only support, I slammed them for it, and it got a lot of attention within the PSP community. A year after I slammed Sony for not putting in real wireless LAN security, it updated the PSP with a newer firmware that did support WPA security. The time has come for the Nintendo community to band together and demand a fix from Nintendo. There are also some other consumer electronics devices that support WEP only, and you'll need to complain to them as well to get a fix.
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George Ou is Technical Director of ZDNet. See his full profile and disclosure of his industry affiliations.
