Nov 12 2008   12:43AM GMT

Wireless: Get Ready to Kiss WPA Goodbye

Arian Eigen Heald Arian Eigen Heald Profile: Arian Eigen Heald

The word is out in InfoSec circles that a practical attack method against WPA – enabled wireless access points has been announced and is to be presented at PacSec in Tokyo this week.

It used to be that only a dictionary attack against WPA-encrypted packets using a weak pre-shared key (PSK) was available; if you had a PSK of more than 8 characters, you could be reasonably assured that you were secure. Now, Erik Tews will be presenting his attack method, which uses a combination of protocol weaknesses and cryptographic weaknesses to compromise TKIP encryption. The attack lets the attacker inject seven packets into the network, per decrypt window.

There’s far reaching ramifications to this attack, but in short terms, this presentation means the days of WPA are numbered. Some of the attack code is known to be already available.

The attack focuses on TKIP encryption, and you may think that with AES enabled, you are safe. Not, however, if your router defaults back to TKIP to enable older clients to connect. Not all routers allow you to disable this feature, either. On some equipment AES is called WPA2 and TKIP is WPA. The WPA spec leaves support of CCMP(AES) optional while the WPA2 spec mandates both TKIP and AES capability.

What to do today (and believe me, I’m checking my home router, and will be auditing routers to this effect in the future; best believe that PCI will update their requirements quickly, as well)? Check your APs (access points) as follows:

Use only AES
Disable Negotiations to TKIP from CCMP(AES).
If you must use TKIP, rekey every 120 seconds.

Interestingly, the amount of time he is estimating is 15 minutes to crack WPA.

What to do going forward? Plan on upgrading your wireless access points sooner rather than later. It won’t be long before some joker is using this attack to break into businesses.

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