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Wireless Security

Wireless Security. Beyond WEP. Wireless Security. Privacy Authorization (access control) Data Integrity (checksum, anti-tampering). WEP. RC4 stream cipher WEP key (40 or 60 bit) combined with 24-bit Initialization Vector (IV) Sender XORs stream cipher with data to encrypt

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Wireless Security

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  1. Wireless Security Beyond WEP

  2. Wireless Security • Privacy • Authorization (access control) • Data Integrity (checksum, anti-tampering)

  3. WEP • RC4 stream cipher • WEP key (40 or 60 bit) combined with 24-bit Initialization Vector (IV) • Sender XORs stream cipher with data to encrypt • IV and ciphertext sent, decoded using IV and stored WEP key

  4. WEP Vulnerabilities • Use of same WEP key among clients • Limited keyspace for IV (16,777,215) • With enough traffic, IVs are re-used • Possible to collect packets with same IV and crack WEP key - then open to data capture and MITM attacks • No key management - WEP key must be changed manually on each NIC

  5. Attempts to secure WEP • Larger WEP key length (Lucent 104/128-bit, Agere 152-bit, USR’s 256-bit) Just takes longer to retrieve WEP key • VPN Can be difficult to achieve seamless routing when APs are crossed

  6. Wi-Fi Alliance introduces WPA • 802.1X EAP mutual authentication or PSK (Pre-Shared Key) • TKIP for encryption • MMIC (Michael Message Integrity Check) for data integrity

  7. 802.1X EAP Mutual Authentication • Port-based access control • Mutual authentication via authentication server

  8. 802.1X EAP has three elements • Supplicant - client device • Authentication Server - RADIUS server or similar • Authenticator - intermediary between Supplicant and Authentication server (usually an AP)

  9. Different types of EAP • LEAP - Cisco proprietary, uses username/password to authenticate against RADIUS • TLS - RFC 2716, uses X.509 certificates for authentication on both Supplicant and Authenticator • TTLS - Developed by Funk Software, Authenticator uses a certificate to identify itself, Supplicant can use username/password • PEAP - Authenticator uses certificate, Supplicant can use username/password

  10. TKIP - Temporal Key Integrity Protocol • Fixes the flaw of key reuse in WEP • Comprised of three parts, guarantees clients us different keys - 128-bit temporal key, shared by clients and APs - MAC of client - 48-bit IV describes packet sequence number

  11. TKIP continued • Uses RC4 like WEP, so only software or firmware upgrade required • Changes temporal keys every 10,000 packets

  12. Michael Message Integrity Check (MMIC) • Message Integrity Code (MIC) - 64-bit message calculated using “Michael” algortithm inserted in TKIP packet to detect content alteration • Protects both data and header • Implements a frame counter, which discourages replay attacks

  13. Two modes of WPA • WPA Enterprise • WPA PSK (Pre-Shared Key)

  14. WPA Enterprise • Requires RADIUS server • Uses RADIUS for both authentication and key distribution • Central management

  15. WPA PSK • No RADIUS server required • Uses shared secret • Management is handled on the AP - Vulnerable to dictionary attacks - Still uses partial shared key

  16. WPA Summary • Requires authentication using 802.1X • Keys change using TKIP • Header as well as payload protected by adding MIC to ICV • Frame counter to lower risk of replay attacks • Still a temporary stopgap to 802.11i and/or WPA2 since it still uses RC4 and PSK uses shared key

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