The Trouble with WEP Or, cracking WiFi networks for fun & profit (not really) Jim Owens

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

Background & history… Wireless Equivalent Privacy Adopted in 1999 as part of standard Later swallowed whole by b 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

How WEP works 1. Plain text gets CRC-32 checksum appended bit initialization vector pre-pended to key as a seed for RC4 key scheduling algorithm 3. RC4’s pseudo-random generation algorithm outputs keystream 4. Keystream XORed with plain text 5. IV in plain text pre-pended to message 6. On receipt, keystream regenerated and XORed with cipher text to produce plain text

WEP’s major weaknesses IV space too small (2 24 ) 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

Wardriving: Kismet Network detector, sniffer, IDS Works on b, a, g 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

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.

Stella, the WiFi attack animal!

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?

Wardriving: Kismet

Wardriving: Attack phase Aircrack-ng: Software for network detection, sniffing, WEP cracking, and analysis Works on b, a, g 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

Wardriving: Aircrack procedure 1.Bring up adapter on target’s channel in monitor mode: # ifconfig wlan0 up # iwconfig wlan0 mode Monitor channel 9 2.Capture packets to file on channel, IVs only # airodump wlan0./berlin_dump 9 1

Wardriving: Airodump

Wardriving: Aircrack procedure 3.Find weakly-encrypted packets to replay in interactive mode # aireplay -2 -b 00:14:6C:40:BA:A6 \ -x 512 wlan0 4.Finally, crack WEP key with captured IVs # aircrack -n 64 berlin-dump.ivs

Wardriving: Aireplay

Wardriving: Aircrack

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!

Questions?