Exam - IEEE 802.11/802.11b

Exam - IEEE 802.11/802.11b

1. IEEE 802.11

   • components
     • wireless station
       • device with wireless network interface card
         • transmitter, receiver
     • wireless acces point
       • bridge between wireless and wired networks
         • transmitter, receiver
         • wired network interface
         • bridging software
   • modes of operation
     • infrastructure
       • intended for wireless devices to connect to an established infrastructure
     • ad hoc
       • intended for spontaneous collection of wireless devices to communicate between themselves w/o an AP
         • peer to peer
         • independent basic service set (IBSS)
   • security measures
     • treat WLAN as untrusted network
       • firewall between WLAN and cabled network
       • intrusion detection system
       • vulnerability assessment
       • use VPN
     • define a wireless network policy
       • acceptable use
       • have cabled LAN fallback
     • discover unauthorized use
       • scan regularly
         • port scanning
         • MAC address sniffing
         • war walking
     • audit access points
       • standard config
       • strong passwords, secure admin interfaces
       • strong WEP key
     • protect wireless stations
       • personal firewall
       • config scanning
       • intrustion detection
     • location
       • position out of line of sight from windows
       • signal should not go outside physical walls
     • MAC address locking
       • Maintani MAC address ACL

2. IEEE 802.11b

   • security mechanisms
     • shared key authentication
       • steps
         • 1. AP sends nonce
         • 2. Station encrypts nonce with shared key & RC4
         • 3. Sends encrypted nonce + 24bit IV
         • 4. AP decrypts nonce.
         • 5. AP compares decrypted nonce value to sent value.
     • Wired Equivalence Privacy (WEP)
       • steps
         • 1. compute integrity check vector. 32 bit cyclic redundancy check.
         • 2. Append to plaintext.
         • 3. Encrypt plaintext with keystream generated from 40bit key and 24 bit initialization vector.
         • 4. Append IV to ciphertext and send.
     • wireless station and AP share fixed, symmetric key
     • weaknesses
       • 1. small initialization vector
         • sent in clear
         • duplicates
           • run passive attack on WEP. collect messages with duplicate IVs and XOR
       • 2. key management
         • user friendly key entry
           • pass phrase key specification reduce the key space to 2^21 values
         • small key space
           • 2^40 effective bits (due to known 24 IV bits)
         • multiple AP key management undefined
           • administrative overhead in configuration
           • greater key exposure with the addition of each AP
         • weak keys
           • Some keys with RC4 determine a large number of predictable values in the keystream.
           • Attack discovered where if a portion of the key is known, the whole key can be determined through an analysis of the keystream.
   • goals
     • access control to wireless network
     • confidentiality over wireless channel
     • Integrity over wireless channel.