W i reless LAN Security Presented by: Pallavi Priyadarshini Student ID

Agenda Brief background on Wireless LAN Basic security mechanisms in WEP Vulnerabilities Enhancing wireless security with WPA Comparing WEP and WPA Conclusion

Brief Background A local area network (LAN) with no wires Several Wireless LAN (WLAN) standards  Mbps speed, 2.4Ghz band  b (Wi-Fi) – 11 Mbps speed, 2.4Ghz band  a (Wi-Fi) - 54 Mbps speed, 5Ghz band  g (Wi-Fi) – 54 Mbps speed, 2.4Ghz band

Wireless network components

Security Challenges and Solutions Challenges  Beyond any physical boundaries  Encryption, Authentication and Integrity Basic Security Mechanisms in  Service Set ID (SSID) – Acts like a shared secret, but sent in clear.  MAC Address Lists – Modifiable and also sent in clear.  The WEP Algorithm

More on WEP Stands for Wired Equivalent Privacy Designed to encrypt data over radio waves Provides 3 critical pieces of security  Confidentiality (Encryption)  Authentication  Integrity Uses RC4 encryption algorithm  Symmetric key stream cipher  64-bit shared RC4 keys, 40-bit WEP key, 24-bit plaintext Initialization Vector (IV)

WEP Encryption and Integrity IV Secret Key SeedPRNG XOR IV Ciphertext Plaintext CRC-32 Algorithm Integrity Check value Plaintext Key Sequence Message PRNG – RC4 Pseudorandom number generation algorithm Data payload

WEP Authentication 2 levels of authentication  “Open” : No authentication  “Shared secret” : Station A Station B Nonce N E(N, K A-B ) Request for shared key auth. Authentication response

WEP – The “flawed” Solution Weakness in key management  Single key for all access points and client radios  Static unless manually changed  Authentication and encryption keys are the same Shared key authentication failure  No knowledge of secret to gain network access  WEP PR =C  P (where C, P are passively recorded) Attacker AP Authentication request Challenge R WEP PR  R Success

WEP – The “flawed” Solution (contd.) Weakness in Encryption  Short 24-bit IV, reuse mandatory  Weak per-packet key derivation - exposes RC4 protocol to weak key attacks. Given c 1 and c 2 with same IV, c 1  c 2 = p 1  p 2 [p 1  S  p 2  S], leading to statistical attacks to recover plaintexts  Short 40-bit encryption scheme No forgery protection  Using CRC-32 checksum possible to recompute matching ICV for changed data bits  Given C= RC4(IV, key) , can find C’ that decrypts to M’=M+Δ such that C’= RC4(IV, key) 

WEP – The “flawed” Solution (contd.) No protection against replays Optional, mostly not turned on by users

Design Constraints WEP patches will rely entirely on software upgrade Access points have little spare CPU capacity for new functions Encryption functions are hard-wired in the access points

Enhancing WLAN Security with WPA WPA - Wireless Protected Access Strong, standards based, interoperable security for Wi-Fi Addresses all known weaknesses of WEP Subset of forthcoming IEEE i standard Designed to run as a software upgrade on most Wi-Fi certified products.

Security Mechanisms in WPA - TKIP Uses TKIP (Temporal Key Integrity Protocol) Encryption. Suite of algorithms wrapping WEP Adds 4 new algorithms to WEP: 1. New cryptographic message integrity code (MIC) called Michael - to defeat forgeries 2. New IV sequencing discipline - to remove replay attacks 3. A re-keying mechanism – to provide fresh encryption and integrity keys

More on TKIP 4. A per-packet key mixing function Phase 1 (Eliminates same key use by all links) - Combines MAC address and temporal key. Input to S- box to produce intermediate key Phase 2 (De-correlates IVs and per-packet keys) - Packet sequence number encrypted under the intermediate key using a fiestel cipher to produce 128- bit per packet key. TKIP leverages 802.1X/EAP framework for key management

802.1X/EAP Architecture Supplicant (wireless client) Authenticator (AP) Authentication Server (RADIUS) EAP-start EAP-identity request EAP-identity response EAP success/reject

WPA Modes of Operation - Pre-shared key vs. Enterprise Pre-shared Key Mode for home/SOHO users  Does not require authentication server  “Shared Secret” or password entered manually in the AP and wireless client.  WPA takes over automatically.  Only the clients with matching passwords are allowed to join the network.  The password automatically kicks off the TKIP encryption process. Enterprise Mode for corporate users  Requires an authentication server like RADIUS  Centralized management of user credentials

WPA modes of operation – Enterprise Mode Wired Network Services Internet Authentication server Access Point

WEP vs. WPA WEPWPA EncryptionFlawedFixes all WEP flaws 40-bit keys128-bit keys Static-same keys used by everyone on network Dynamic session keys. Per-user, per-session, per-packet keys Manual distributionAutomatic Distribution AuthenticationFlawed, uses WEP key itself Strong user authentication using 802.1X and EAP

Comparing WPA and i i 802.1X Key management Cipher & Authentication negotiation TKIP AES WPA

Conclusion WPA is not an ideal security protocol design… However, it is a dramatic improvement in Wi- Fi security. Has not been broken (yet). Protects the original hardware investment. If hardware constraint removed, a more robust security solution possible. Such a solution is being developed based on a even stronger cryptographic cipher - Advanced Encryption Standard (AES).

References [1] Bruce Potter & Bob Fleck, “ Security”, O-Reilly, December 2002 [2]James larocca & Ruth larocca, “ Demystified”, McGraw-Hill Telecom, 2002 [3]Whitepaper on Wireless LAN Security on [4] x.html