Crypto U12, WLAN

Crypto U12, WLAN

1. background

   • 3 standards
     • WEP
       • original standard
       • wired equivalent privacy
       • designed to provide security at data link layer
       • replaced by WPA
     • WPA
       • designed as stop gap for WEP insecurity
       • WiFi Protected Access
       • 2002
       • designed to work with legacy hardware
     • WPA2
       • IEEE 802.11
       • 2004

2. design

   • originally designed to provide security equivalent as a cabled network and no more
   • support open standards to assure support for all connecting devices
   • does not need to be as flexible as SSL so fewer supported algorithms can be selected
   • symmetric crypto used
     • because speed is desired
     • because it is a closed environment and easier to control
   • only as flexible as needed, but not more
   • need to be able to provide quick updates

3. security requirements

   • confidentiality
   • mutual entity authenticaton
   • data origin authentication

4. WPA

   • differences from WEP
     • uses stronger authntication and key establishment
       • key hierarchy used
         • uses master key, key ecrypting keys and data keys
       • mutual entity authentication
       • mutual data origin authentication
       • mutual key establishment
       • key confidentiality
       • key freshness
       • mutual key confirmation
       • unbiased control
       • 2 methods to establish Pre-Master-Key (PMK)
         • Extensible Authentication Protocol (EAP)
         • Established as a preshared key
   • WPA
     • uses Rc4
     • mixes data encrypting key with IV (rather than appending)
     • for each package, a new IV sent
   • WPA2
     • uses AES
     • provides confidentiality and data origin authentication with CCMP
       • CBC - MAC protocol
         • 1. create MAC using CBC
         • 2. encrypt using counter mode

5. WEP

   • implementation
     • RC4 Stream Cipher
       • 40 bit key
       • stream cipher desirable since transmission prone to errors
       • @ the time, cipher was well respected
     • CRC checksum for integrity
     • simple challenge and response for authentication
     • use shared, fixed symmetric key for each WLAN
       • If one device on network compromised, they are all compromised.
     • RC4 required synchronization
       • this means each packet must be encrypted separately, so this runs the risk of keystream being used repeatedly
         • to provide variation, used an initialization vecor of 24 bits and appends it to key
           • PROBLEM: RC4 does not originally support initialization vectors
   • security issues and design flaws
     • single, shared key is a single point of failure
     • since WEP key is used for every encryption, it is continuously exposed
     • abuses principle of key separation
     • key length not future proof (40 bits)
     • nonstandard use of crypto algorithm
     • lack of origin authentication
     • weak entity authentication mechanism
   • attacks
     • man-in-the-middle
       • because only supports unilateral entity auth (Alice to access point)
     • replay attack
     • CRC manipulation attack
     • birthday attack on IVs
     • key recovery attack