1. WLANs & Security Standards (802.11) 802.11b - up to 11 Mbps, several hundred feet 802.11g - up to 54 Mbps, backward compatible, same frequency 802.11a - up to 54 Mbps, emerging standard bluetooth - 1 Mbps Why wireless? Security Issues - to be continued... Legal & Social Issues - who owns the bandwidth? “Wireless local area networking has taken the world by storm. As is often the case, proper security was not built in at the beginning, and the act of retrofitting it has not been without difficulty” -- Aviel Rubin, Technical Director of the Information Security Institute, Johns Hopkins University “Wireless local area networking has taken the world by storm. As is often the case, proper security was not built in at the beginning, and the act of retrofitting it has not been without difficulty” -- Aviel Rubin, Technical Director of the Information Security Institute, Johns Hopkins University

2. 802.11 Crash Course What does the AP do? Station (radio) communication - protocols rely upon media access control (MAC) addresses Access Point Station network Where are the vulnerabilities? - packets are called MPDUs these include a frame sequence number and CRC-32 - packets are called MPDUs these include a frame sequence number and CRC-32

3. 802.11 Security - optional - based on challenge and response protocol Wired Equivalent Privacy (WEP)

4. Challenge and Response Exchange Premise: verify the correctness of a password without sending it Given: - two systems (client & server) that share a symmetric key - a server that “knows” the password Given: - two systems (client & server) that share a symmetric key - a server that “knows” the password 1.. client requests password from user Note: Many systems use this protocol - e.g. Windows Web site authentication Note: Many systems use this protocol - e.g. Windows Web site authentication client system server system 2.. client sends random block of data (challenge) to server 3.. server uses password to encrypt challenge 4.. server sends encrypted data (response) 5.. client uses user-supplied password to encrypt the challenge 6.. the user’s password is correct iff the encrypted challenge identical to the response

5. 802.11 Security - optional - based on challenge and response protocol - uses RC4 (symmetric) algorithm - uses 24-bit nonce (challenge) per packet (called initialization vector (IV) Wired Equivalent Privacy (WEP) - note that WEP does not specify any way to obtain shared keys

6. 802.11 Security Problems - identity of a package is based upon the client MAC address - open source drivers typically permit user to alter MAC addresses 1) relies upon an access control list in the AP - these are stored by MAC address 1) relies upon an access control list in the AP - these are stored by MAC address Identity 2) “closed network” - use proprietary mechanism based upon a shared “secret” string that is broadcast in cleartext within management frames. 2) “closed network” - use proprietary mechanism based upon a shared “secret” string that is broadcast in cleartext within management frames. Access Control (two alternatives) Authentication (two alternatives) 1) open system - AP permits everyone to authenticate 2) challenge & response between station and AP 2001 - RC4 is found to be vulnerable to attack given millions of cleartext - ciphertext pairs 2001 - RC4 is found to be vulnerable to attack given millions of cleartext - ciphertext pairs The RC4 attack on WEP is automated with publicly released tools.

7. Current 802.11 “Solutions” 1) place WLAN outside firewalls 2) use virtual private networks (VPN) Note that VPNs work with IP-based protocols, but WLANs rely upon MAC-based protocol. Note that VPNs work with IP-based protocols, but WLANs rely upon MAC-based protocol.

8. Future 802.11 Standards (in progress) - will arrive in the form of firmware & driver patched (when released) - message integrity code (MIC) included to eliminate forgeries - uses a 48-bit IV, instead of 24 bits used by WEP Temporary Key Integrity Protocol (TKIP) CCMP - packet sequencing rules changed to prohibit replay attacks - a per packet key mixing function used to prevent key cracking - TKIP is a patch for WEP - uses AES, instead of RC4 - uses larger MIC than TKIP - intended as eventual replacement for TKIP