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IEEE 802.11i

IEEE 802.11i. IT443 Broadband Communications Philip MacCabe October 5, 2005 http://www.maccabe.org/index.php/Phil_MacCabe:BYU_Information_Technology. Overview. Introduction The Need for a New Standard WEP, WPA, TKIP and other alphabet soup Wi-Fi Protected Access 2 (WPA2)

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IEEE 802.11i

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  1. IEEE 802.11i IT443 Broadband Communications Philip MacCabe October 5, 2005 http://www.maccabe.org/index.php/Phil_MacCabe:BYU_Information_Technology

  2. Overview • Introduction • The Need for a New Standard • WEP, WPA, TKIP and other alphabet soup • Wi-Fi Protected Access 2 (WPA2) • Four Way Handshake • Group Key Handshake

  3. Obsolete Wireless Security • Wired Equivalent Privacy (WEP) • Stream Cipher RC4 for Confidentiality • CRC-32 Checksum for Integrity • 64 bit WEP = 40 bit key + 24 bit Initialization Vector (IV) • Exploits can recover key in a few hours from more than a mile away • Is optional, therefore not always turned on • Has no Key Management, rather a single shared key • 2005, FBI demonstrated cracking WEP in less than 3 min.

  4. Stopgap Security • Wi-Fi Protected Access (WPA) • Runs on legacy hardware • Wi-Fi Alliance's solution until a standard could be formed, and new hardware made • Temporal Key Integrity Protocol (TKIP) • Per Packet Key Mixing • Message Integrity Code • Re-keying Mechanism • Hashes IV to prevent related key attack • This was intended to be replaced by IEEE 802.11i (WPA2)

  5. IEEE 802.11i • Draft Standard Approved on 24 July 2004 • Uses Advanced Encryption Standard (AES) block cipher • Designed for use on top of 802.1X authentication i.e. Extensible Authentication Protocol (EAP) and an authentication server • Robust Security Network (RSN) • Counter-Mode/CBC-Mac Protocol (CCMP) is AES-based encyption providing confidentiality, integrity, and origin authentication

  6. Counter-Mode Encryption

  7. Cipher Block Chaining

  8. Attacks & Errors

  9. Four Way Handshake • After EAP authentication the AP still needs to authenticate itself to the client station (STA). • Keys still need to be derived • EAP provides Pairwise Master Key (PMK) • This handshake creates a Pairwise Transient Key (PTK) • PMK+Anonce+Snonce+AP MAC Address+STA MAC AddressHash AlgorithmPTK • Nonce are random throwaway numbers

  10. Four Way Handshake

  11. PTK is split into 3 keys • EAPOL-Key Confirmation Key (KCK) • For generating MIC for packets • EAPOL-Key Encryption Key (KEK) • Provides confidentiality for packets • Temporal Key (TK) • Used to encrypt actual wireless traffic

  12. Group Key Handshake • Group Transient Key (GTK) is used by all devices on network • Updated after a certain time limit or when a device leaves the network • Allows devices to receive broadcast and multicast packets • Update Process • AP sends out new GTK using each station's PTK • STA acknowledges the new GTK and responds • A MIC is used to prevent tampering

  13. Pre-Shared Key Mode • Designed for home and small office use • Replaces 802.1X EAP server with a passphrase used to access the network • Susceptible to password cracking

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