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DIMACS November 3-4, 2004 Workshop: Mobile and Wireless Security

WIRELESS SECURITY AND ROAMING OVERVIEW. DIMACS November 3-4, 2004 Workshop: Mobile and Wireless Security Nidal Aboudagga*, Jean-Jacques Quisquater UCL Crypto Group Belgium. Outline. Introduction WEP IEEE 802.1X WPA IEEE 802.11i Roaming Conclusion. Why Wireless?. Mobility

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DIMACS November 3-4, 2004 Workshop: Mobile and Wireless Security

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  1. WIRELESS SECURITY AND ROAMING OVERVIEW DIMACS November 3-4, 2004 Workshop: Mobile and Wireless Security Nidal Aboudagga*, Jean-Jacques Quisquater UCL Crypto Group Belgium

  2. Outline • Introduction • WEP • IEEE 802.1X • WPA • IEEE 802.11i • Roaming • Conclusion

  3. Why Wireless? • Mobility • Flexibility • Rapid deployment • Easy administration • Low cost • Simplicity of use • used in two modes: • Ad-Hoc • Infrastructure mode

  4. Wired Equivalent Privacy (WEP) (1) • Tried to ensure • Confidentiality • Integrity • Authenticity • Replaces the so-known MAC-address filtering • Uses the RC4 encryption algorithm to generate a key stream • Uses a shared key K (40bit/104bit)

  5. Wired Equivalent Privacy (WEP) (2)

  6. Wired Equivalent Privacy WEP (3) • Uses standard challenge response • An initialization vector, IV/(24bit): per packet number, sent in clear • WEP failed, because of many known attacks • IV Collision • Message injection • Authentication spoofing • Brute Force Attack • Weaknesses in the Key Scheduling Algorithm of RC4……)

  7. Network port authentication 802.1x (1) • Adapted to wireless use by IEEE 802.11 group • Based on Extensible Authentication Protocol (EAP) • Three elements are in use with 802.1x • Supplicant (user) • Authenticator (access point) • Authentication server (usually RADIUS) • Uses key distribution messages

  8. IEEE802.1x Access Control

  9. IEEE 802.1x EAP authentication

  10. 802.1X / EAP: Authentication methods • EAP-MD5: Vulnerable to a lot of attacks and did not support dynamic WEP keys • EAP-TLS: Uses certificates for servers and users. The user’s identity is revealed • EAP-TTLS: Uses server’s certificate. Protects user’s identity • PEAP: Similar to EAP-TTLS, used by Cisco and Microsoft in their products • LEAP: A Cisco proprietaryvulnerable to dictionary attacks, • EAP-SIM, EAP-SPEKE,…

  11. Wifi-Alliance Protected Access (1) • Built around IEEE 802.11i (draft 3) and compatible with existing material • Address WEP vulnerability • Supports mixed environment • Uses Temporal Key Integrity Protocol (TKIP), 128 bit RC4 key • The use of AES is optional

  12. Wifi-Alliance Protected Access (2) • A suite of 4 algorithms composes TKIP • A Message Integrity Code (MIC), called Michael to defeat forgeries • A new Initial Vector sequencing discipline, to prevent replay attacks • A key mixing function, to have a per-packet key • A re-keying mechanism, to provide fresh keys to the key mixing function

  13. TKIP encapsulation

  14. Wifi-Alliance Protected Access (3) • Solves the problems of integrity, authentication, forgery and replay attack in network with RADIUS server • In small network, WPA uses shared secret pass-phrase. This mode is vulnerable to the dictionary attack and impersonation • Preserves the RC4 algorithm with its known weakness to ensure compatibility

  15. 802.11i / Robust Security Network (RSN) • Uses AES by default to replace RC4 • Used in CCM mode: CTR + CBC-MAC • CCMP fixes 2 values of CCM parameters • M=8, indicating that the MIC is 8 octets • L=2, indicating the lenght field is 2 octets • Support Quality of Service • Support of preauthentication to enhance the roaming in wireless network

  16. CCMP Encapsulation

  17. Roaming • Roaming with full authentication IEEE 802.1x/EAP or PSK (very big latency time) • Roaming to AP with whish cached a shared PMK from previous SA • skip authentication steps • use 4-way handshake key management protocol to negociate session key (PTK) and send (GTK) • useless when user roams to new AP • Preauthentication: the STA authenticate without association to another AP before leaving the old one

  18. Full authentication

  19. Preauthentication

  20. Problems of preauthentication • Preauthentication enhances the performance of roaming but the handoff latency limits the performance for multimedia applications • Preauthentification can only be used in the same ESS (extended set of service) • Preauthentication is an expensive computational load which may be useless

  21. Fast roaming • IEEE 802.11r WG to enhance fast roaming performance • It reduces the hand-off latency of the 4-way handshake protocol (creating alternative optional 3-way handshake) • Adopt roaming key hierarchy • to minimize computational load • time dependency of KMP and • precomputation of roaming key R-PTK • Other works attempt to reduce probing latency IEEE802.11f

  22. Conclusion • When IEEE 802.11k is ratified, will improve roaming decisions with a site report sent to client STA • Until now no efficient agreed solution to the inter-LAN and inter-WAN roaming • When the work of IEEE 802.11r group is finished, the wireless network will be more convenient to mobile users with multimedia applications • The IEEE 802.11i is new and will need time to reach maturity. It solves many problems of security. Many others are not under its responsibility (DoS, RF jamming,…)

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