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IEEE 802.11 Security

IEEE 802.11 Security. Specifically WEP, WPA, and WPA2. Brett Boge, Presenter CS 450/650 University of Nevada, Reno. Introduction / History. IEEE 802.11 standard for wireless LAN (802.11-1997) Ratified September 1999 WEP included

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IEEE 802.11 Security

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  1. IEEE 802.11 Security Specifically WEP, WPA, and WPA2 Brett Boge, Presenter CS 450/650 University of Nevada, Reno

  2. Introduction / History • IEEE 802.11 standard for wireless LAN (802.11-1997) • Ratified September 1999 • WEP included • 2001 UC Berkeley Fluhrer, Mantin, and Shamir"Weaknesses in the Key Scheduling Algorithm of RC4“ • ~2002 WPA • 2004 802.11i ratified with WPA2 • IEEE 802.11-2007

  3. WEP Wired Equivalent Privacy • Part of the original 802.11 standard • Uses RC4 for confidentiality • Uses CRC32 for integrity • 64 bit WEP uses a 40-bit key (aka WEP-40) • Limited by the government • 128 bit WEP uses a 104-bit key • Deprecated in 2004

  4. RC4 • 1987, "Rivest Cipher 4“, aka “Ron’s Code” • 1994 spread on the internet • Stream cipher • KSA (Key scheduling algorithm): • S[i] = {0,1,2,3…} • j = 0 • for i = 0 – 255 • j := (j + S[i] + key[i mod keylength]) mod 256 • swap values of S[i] and S[j] • end

  5. RC4 • PRGA: • i = 0 • j = 0 • as long as we need output: • i = (i + 1) mod 256 • j = (j + S[i]) mod 256 • swap S[i] and S[j] • output S[(S[i] + S[j]) mod 256]

  6. WEP • Uses RC4 for encryption • Uses CRC32 for integrity Encryption:

  7. Initialization Vector • Fixed-sized input into a crypto function • Prevents repetition • Uniqueness important • WEP uses 24 bit

  8. WEP “Authentication” 2 Methods

  9. Attacking WEP Fluhrer, Mantin, and Shamir • 2001 “Weaknesses in the Key Scheduling Algorithm of RC4” • Key recovery • Requires a sufficiently large number of messages • Exploits weak IVs With certain weak IVs, knowing the nth byte of a keystream allows the attacker to derive the n+1th byte. IV’s of form (a + 3, n − 1, x) will help to provide a possible key value at index a

  10. Additional WEP Weaknesses • No key management, shared key • Statistical attack against duplicate IVs • 2005 - FBI showed that WEP can be cracked in 3 minutes usingpublicly available tools • More correlations between the keystream and the key thanshowed by Fluhrer, Mantin, and Shamir (KSA weaknesses) • 2007 - Erik Tews, Andrei Pychkine, and Ralf-Philipp Weinmann 104bit WEP key: 50% - 40,000 80% - 60,000 95% - 80,000

  11. WPA Wi-Fi Protected Access • 2002 Wi-Fi AllianceWPA stopgap until 802.11i • No shared key, uses TKIP • 128 bit • Per-packed • Subject to old weaknesses • Uses RC4 to run on old hardware • Stronger Integrity, no CRC, uses MACs

  12. WPA2 Wi-Fi Protected Access • 2004 Wi-Fi AllianceIEEE 802.11i-2004 • No TKIP, uses CCMP as standard • Counter Mode with Cipher Block ChainingMessage Authentication Code Protocol • Block Cipher using AES • Mandatory for all devices bearing the Wi-Fi mark

  13. WPA/WPA2 Authentication

  14. Conclusion • WEP • Many weaknesses, deprecated • WPA • uses weaker TKIP, better than WEP • Less intensive • Supported on older equipment • WPA2 • uses AES • 802.11i standard • Despite wireless security, using a tunnel (IPsec, SSH) • when on a wireless network is a good idea to double your • Protection.

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