Wireless Network Security CSIS 5857: Encoding and Encryption

Wireless LAN Terminology Station: Device capable of IEEE wireless connectivity (wireless laptop, etc.) Distribution System: Backbone system for long- distance communication (lines/satellite/etc.) Access point: Bridge between station and distribution system (or between stations in same BSS) Basic Service Set (BSS): Set of stations in range of access point

Wireless LAN Structure

Differences from LAN security: Any transmission may be listened to by any device in range of access point  All transmissions must be secured Other wireless devices in range of AP can attempt to connect to it  Any device wishing to communicate through access point must be authenticated

802.11i RSN Services Access control: –Preventing access to access point until authentication Authentication: –Mutual authentication between stations and access points, and key generation Privacy: –Encrypting/hashing/etc. of messages to insure confidentiality/information integrity/etc.

Authentication Server Authentication server –Contacted by AP when station requests access –Uses authentication protocol to establish station identity –AP blocks communication with rest of network until authentication complete

IEEE i Operation Phases

Discovery Phase Station contacts AP –Challenge-response can be used to authenticate AP Station passes security suite to AP (like SSL) AP responds with chosen algorithms

Authentication Phase Station sends request to AP for connection to authentication server Extensible authentication protocol (EAP) used for mutual authentication AS generates keys for secure information exchange

Authentication Phase Extensible Authentication Protocol: –Based on challenge-response –Station and AS share secret information (such as symmetric key) –AS sends challenge to station (via AP) –Station sends response –May repeat with multiple challenges (10 – 20) for added protection against replay attacks

Key Management Phase Possible methods: –Station and AP already share pre-shared key (PSK) previously installed on station –AS generates and sends master session key (MSK) to station as part of EAP challenge response Used to generate pairwise master key

Key Management Phase HMAC-SHA1 used to generate Pairwise transient key from –Pairwise master key –MAC address of station and AP (prevents replay attacks) PTK consists of –Key used for confirmation of other keys –Key used to encrypt other keys –Actual temporal key used to securely transmit data

Key Management Phase Handshake between station and AP used to establish and confirm keys used for secure transmission