WEP Cracking

WEP is infamously known as the broken wireless security protocol. A design flaw was discovered in 2001 and after several cascading discoveries it's now possible to crack a WEP protected network within minutes. WPA is the successor to WEP and features a better but not perfect security protocol.

Background

There are now many sources that describe the vulnerability in detail and APR replay to generate traffic, but this is a short summary.

• WEP encryption: 24-bit counter (unencrypted) + 104-bit key, 128-bit key -> use to generate RC4 cipher stream -> XOR the message -> Encrypted packets
• ARP replay: On the basis that the first 12-bytes of ARP packets always is the same -> Capture one ARP packet -> Inject back to into the network to force data traffic to happen -> XOR back first 12-bytes of each ARP/data packet -> After 10-20000 packets, enough small piece, 12-bytes, of the pseudorandom RC4 stream cipher is gathered
• Key crack: Perform statistical analysis on the collected data to find each byte in the final key -> Try to decrypt captured data to verify key

References

• How to Crack a Wi-Fi Network's WEP Password with BackTrack
• SpoonWEP for Noob
• Part 10: WPA-PSK Cracking with a dictionary attack in Backtrack 3
• Cracking WEP Using Backtrack: A Beginner’s Guide
• Remote-Exploit Backtrack
• Cracking WPA FAST with video cards