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 IV and ciphertext sent, decoded using IV and stored WEP key

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

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

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

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

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)

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

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

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

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

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

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

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

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 i and/or WPA2 since it still uses RC4 and PSK uses shared key