cse 5/7349 – april 5 th 2006 wireless networking
DESCRIPTION
FECTRANSCRIPT
CSE 5/7349 – April 5th 2006
Wireless Networking
Compression
FEC
CRC
Modulation
Bits / Symbols / Baud
DSSS / FHSS
Wireless Security History
• Cordless Phones• Baby Monitors• Networking
802.11 Components
802.11 modes
• Infrastructure mode• Ad-hoc mode (peer-to-peer)
Infrastructure mode
Basic Service Set (BSS) – Single cell
Extended Service Set (ESS) – Multiple cells
Access Point
Station
Ad-hoc mode
Independent Basic Service Set (IBSS)
Open System Authentication
MAC Address Locking
Interception Range
Basic Service Set (BSS) – Single cell
Station outsidebuilding perimeter.
100 metres
Interception
Directional Antenna
• Directional antenna provides focused reception.
• D-I-Y plans available.– Aluminium cake tin.– 11 Mbps at 750 meters.
– http://www.saunalahti.fi/~elepal/antennie.html
802.11b Security Services
Wired Equivalence Privacy
WEP – Sending
Initialization Vector
WEP – Receiving
Shared Key Authentication
• When station requests association with Access Point– AP sends random number to station– Station encrypts random number
• Uses RC4, 40 bit shared secret key & 24 bit IV– Encrypted random number sent to AP– AP decrypts received message
• Uses RC4, 40 bit shared secret key & 24 bit IV– AP compares decrypted random number to
transmitted random number
Security - Summary
• Shared secret key required for:• Messages are encrypted.• Messages have checksum.• But SSID still broadcast in clear.
Security Attacks
802.11 Insecurities
IV Collision attack
Limited WEP keys
Brute Force Key Attack
128 bit WEP
IV weakness
Wepcrack
Airsnort
Safeguards
Wireless as Untrusted LAN
• Treat wireless as untrusted.– Similar to Internet.
• Firewall between WLAN and Backbone.• Extra authentication required.• Intrusion Detection
– WLAN / Backbone junction.• Vulnerability assessments
Discover Unauthorised Use
• Search for unauthorised access points or ad-hoc networks
Location of AP
IPSec VPN
IEEE 802.11i
802.11i – Encryption Enhancements