The Trouble with WEP

1. Or, cracking WiFi networksfor fun & profit (not really) Jim Owens The Trouble with WEP

2. Overview Background and a little history How WEP works WEP’s major weaknesses A short course in wardriving Using kismet to scout out the wireless landscape Zeroing in with the aircrack-ng suite airodump, to capture traffic aireplay, to replay weakly encrypted packets aircrack, to find the key using statistical methods

3. Background & history… Wireless Equivalent Privacy Adopted in 1999 as part of 802.11 standard Later swallowed whole by 802.11b standard Initially, used only 40-bit encryption keys, due to technology export restrictions Later, expanded to 104-bit keys when export restrictions were eased Used 6 times as often as WPA/WPA2 despite known fatal weakness* (85% / 14% / 1%) *Based on a 2006 survey in Seattle area

4. How WEP works Plain text gets CRC-32 checksum appended 24-bit initialization vector pre-pended to key as a seed for RC4 key scheduling algorithm RC4’s pseudo-random generation algorithm outputs keystream Keystream XORed with plain text IV in plain text pre-pended to message On receipt, keystream regenerated and XORed with cipher text to produce plain text

5. WEP’s major weaknesses IV space too small (224) On a busy network, IVs must repeat in <= 5 hours 50% probability that IV repeats in 5,000 packets RC4 algorithm produces “weak” IVs that can be correctly guessed 5% or 13% of the time No key management; typically just one key IP traffic contains much known plaintext data Open to injected traffic that is rebroadcast

6. Wardriving: Kismet Network detector, sniffer, IDS Works on 802.11b, 802.11a, 802.11g networks Uses passive monitoring, so hard to detect Logs sniffed packets in formats compatible with Wireshark/Tcpdump, Airsnort Channel surfs automatically Optionally, supports GPS for network location

7. Kismet: Install & configure Binary packages available for most systems Requires WiFi adaptor that supports monitor mode as “capture source” Logs traffic in popular formats* Specify source in /etc/kismet/kismet.conf, as driver,device,source_name source=ipw2200,eth1,Stella *Wireshark, Airsnort, etc.

8. Stella, the WiFi attack animal!

9. Wardriving: Recon phase Use Kismet to survey WiFi landscape and to choose a target network Record necessary data for Aircrack attack: Channel number? SSID? Access point MAC address?

10. Wardriving: Kismet

11. Wardriving: Attack phase Aircrack-ng: Software for network detection, sniffing, WEP cracking, and analysis Works on 802.11b, 802.11a, 802.11g Uses passive monitoring & packet injection Main tools aircrack-ng: Cracking airdecap: Packet decryption airmon: Monitor mode switching aireplay: Packet injection (Linux only) airodump: Exports traffic to .cap files

12. Wardriving: Aircrack procedure Bring up adapter on target’s channel in monitor mode: # ifconfig wlan0 up# iwconfig wlan0 mode Monitor channel 9 Capture packets to file on channel, IVs only# airodump wlan0 ./berlin_dump 9 1

13. Wardriving: Airodump

14. Wardriving: Aircrack procedure Find weakly-encrypted packets to replay in interactive mode # aireplay -2 -b 00:14:6C:40:BA:A6 \ -x 512 wlan0 Finally, crack WEP key with captured IVs# aircrack -n 64 berlin-dump.ivs

15. Wardriving: Aireplay

16. Wardriving: Aircrack

17. Summary WEP has numerous serious flaws WEP's flaws are thoroughly documented WEP is readily exploitable in a short time, by unskilled attackers, using readily available tools Strong protection is readily available Bottom line: Don't use WEP, period!

18. Questions? That's all, folks!!!