1. Wireless & Personal Communication Systems – CSE5807 Lecture: 10 1 Wireless Personal Communications Systems – CSE5807 Lecture: 10 Stephen Giles and Satha K. Sathananthan School of Computer Science and Software Engineering Monash University Australia These slides contain figures from Stallings, and are based on a set developed by Tom Fronckowiak.

2. Wireless & Personal Communication Systems – CSE5807 Lecture: 10 2 Wireless Security Inherently insecure compared to wired networks. –Broadcast nature of the channel. Increased security requirements. –Wireless networks for internet access, e-commerce, credit-card transactions, etc. Privacy requirements: –Control information. Call setup information, user location, user ID, credit-card information, etc. –Voice or data. Security measures and limitations: –Must consume as little power as possible. –Preserve spectrum efficiency. –Errors in transmission.

3. Wireless & Personal Communication Systems – CSE5807 Lecture: 10 3 Wireless Security Services Confidentiality/Privacy: –Prevention of unauthorized disclosure of information. –Security attack: Interception. –Authentication and encryption. Integrity: –Prevention of unauthorized modification of information. –Security attack: Modification and Impersonation. Availability: –Property of being accessible and useable upon demand by an authorized user. –Security attack: Denial of service.

4. Wireless & Personal Communication Systems – CSE5807 Lecture: 10 4 Wireless Security Services Nonrepudiation: –Service against the denial by either party of creating or acknowledging a message. –Security attack: Fabrication –Security measure: Digital signatures based on public key encryption. Access Control: –Enables only authorized entities to access resources. –Security attack: Masquerading

5. Wireless & Personal Communication Systems – CSE5807 Lecture: 10 5 Encryption Used in wired and wireless networks for providing several security services: –Confidentiality, message authentication, nonrepudiation, access control and identification. –Availability can not be guaranteed. Scrambling the message using a key. Encryption Message (Plaintext/Clear-text) Encrypted Message (Cipher-text) x Y=E k (X) Decryption Encrypted MessageMessage Y M=D k (Y)=X

6. Wireless & Personal Communication Systems – CSE5807 Lecture: 10 6 Secret-Key/Symmetric Key Encryption Sharing a secret key for encryption and decryption. Encryption Y=E k (X) : Ciphertext X=D k (Y) : Plaintext X Insecure Channel Decryption Secure Channel YX kk Advantage: Fast and suitable for high data rates. Disadvantage: Secret key distribution. Examples: –Data Encryption Standard (DES) –Advanced Encryption Standard (AES) –RC-4

7. Wireless & Personal Communication Systems – CSE5807 Lecture: 10 7 Public Key Encryption Using the public key and the private key for encryption and decryption respectively. –Public key is known to everyone. –Only owner can decrypt the message. Large key sizes. –Mathematical operations are quite computationally intensive. –Rarely used in bulk data transfer. –Used to exchange a session key between a pair of communicating entities. Use the session key with secret-key algorithim. Encryption Y=E kpub (X) : Ciphertext X=D kpri (Y) : Plaintext X Insecure Channel Decryption YX K pub, A K pri, A

8. Wireless & Personal Communication Systems – CSE5807 Lecture: 10 8 Attacks on Wireless LANs Passive attacks (Eavesdropping) –Not connected to the network. Listen to packets traversing the wireless segment and gather valuable information. Leave no trace of presence. Active attacks –Connecting to a wireless network through an access point. –Gathering information and changing the configurations. Jamming –Shut down the wireless network by an overwhelming RF signal. –RF signal Intentional or unintentional Removable or non-removable –RF spectrum analyzer can be used to locate the RF signal.

9. Wireless & Personal Communication Systems – CSE5807 Lecture: 10 9 Attacks on Wireless LANs Man-in-the-middle attacks –Uses an access point to effectively hijack mobile nodes by sending stronger signal than the legitimate access point is sending. Mobile nodes then associate to this rogue access point. Gathering sensitive data. Undetectable by users. –Physical security can prevent this attack.

10. Wireless & Personal Communication Systems – CSE5807 Lecture: 10 10 Wireless LAN Authentication IEEE802.11 specifies two methods of authentication: –Open System Authentication –Shared Key Authentication Open System Authentication –Based on SSID only. –Option of using WEP for only encrypting data. AP LAN Authentication Request Frame Authentication Response Frame

11. Wireless & Personal Communication Systems – CSE5807 Lecture: 10 11 Wireless LAN Authentication Shared Key Authentication –WEP key can be used to verify a client's identity and for encryption of data. AP LAN Request to Authenticate Sends a challenge phrase Encrypts the phrase and sends it back Verifies the phrase and if they match authenticates Clients connects to the network

12. Wireless & Personal Communication Systems – CSE5807 Lecture: 10 12 Wired Equivalent Privacy (WEP) Authenticating users and encrypting data payloads. Use pseudo-random number generator (PRNG) and RC4 stream cipher. –RC4 is fast and simple to encrypt and decrypt. Both the sender and receiver use the stream cipher to create identical pseudorandom strings from the known shared key. The sender XORS the plaintext with the stream cipher producing cipher text. The ciphertext is then pretended with the plaintext initialization vector (IV).

13. Wireless & Personal Communication Systems – CSE5807 Lecture: 10 13 Wired Equivalent Privacy (WEP)

14. Wireless & Personal Communication Systems – CSE5807 Lecture: 10 14 Wired Equivalent Privacy (WEP) WEP is simple  Weak RC4 algorithm was inappropriately implemented yielding a less than adequate security solution. –Most implementation of WEP initialize hardware using an IV of 0, thereafter incrementing the IV by 1 for each packet sent. –Length of plaintext IV is 24-bits. –All possible IVs (2 24 ) would be exhausted in 5 hours for a busy networks. Reinitialized starting at zero at least once every 5 hours. Open door for hackers. Flawed process in WEP causes: –Active and passive attacks to decrypt traffic. –Active attacks to inject new traffic.

15. Wireless & Personal Communication Systems – CSE5807 Lecture: 10 15 Wired Equivalent Privacy (WEP) Why WEP was chosen? –The IEEE802.11 standard specifies the following security criteria: Exportable Reasonably strong Self-synchronizing Computationally efficient Optional –WEP met all these requirements when it was introduced. Pushed by WLAN market. –The IEEE802.11 standard leaves WEP implementation up to WLAN manufacturers. Various implementation.

16. Wireless & Personal Communication Systems – CSE5807 Lecture: 10 16 Wired Equivalent Privacy (WEP) WEP Keys: –Core functionality of WEP. –Alphanumeric character string. –Implemented on client and infrastructure devices on a WLAN. –Available in two types, 64-bit and 128-bit. Sometimes referenced as 40-bit and 104-bit since 24-bit IV is concatenated with a secret key. –WEP key can be used: To verify the identity of an authenticating station. For data encryption. –WEP Key distribution: Static Keys Centralized encryption key server.

17. Wireless & Personal Communication Systems – CSE5807 Lecture: 10 17 Wired Equivalent Privacy (WEP) Static WEP Key: –Manually assign a WEP key to an access point and its clients. –Susceptible to security failure. –Suitable for small and simple WLANs. –Multiple WEP keys simultaneously. Centralized Encryption key Server: –Automated process between stations, access points and the key server. Centralized key generation and distribution. Ongoing key rotation. Reduced key management overhead. –Key generation based on a per-packet or per-session or other method.

18. Wireless & Personal Communication Systems – CSE5807 Lecture: 10 18 Wired Equivalent Privacy (WEP) WEP Usage: –Beacons are not encrypted. –WEP encryption/decryption process consumes CPU cycles and reduces the effective throughput. Additional CPU in access points. Implementation in software => More effects Implementation in hardware => Added cost

19. Wireless & Personal Communication Systems – CSE5807 Lecture: 10 19 Advanced Encryption Standard (AES) Replacement for the RC4 algorithm used in WEP. Is being considered in IEEE802.11i standard => WEPv2 AES uses the Rijndael algorithm using 128-bit or 192-bit or 256-bit key. Considered to be an un-crackable.

20. Wireless & Personal Communication Systems – CSE5807 Lecture: 10 20 Filtering Basic security mechanism in addition to the WEP. Keep out that which is not wanted, and to allow that which is wanted. Three types of filtering: –SSID Filtering –MAC Address Filtering –Protocol Filtering

21. Wireless & Personal Communication Systems – CSE5807 Lecture: 10 21 Filtering SSID Filtering: –SSID of WLAN station must match the SSID on the access point. SSID is broadcast in every beacon. If SSID is removed from beacon, the client must have matching SSID => “Closed system”. –Not considered as a reliable method of keeping unauthorized users out of a WLAN. Should be used as a means of segmenting the network. –Common issues: Using the default SSID. Unnecessary broadcasting of SSIDSs.

22. Wireless & Personal Communication Systems – CSE5807 Lecture: 10 22 Filtering MAC Address Filtering: –Network administrator can compile and, distribute and maintain a list of allowable MAC address and program them into each access points. Can be implemented in RADIUS servers instead of each access points. –MAC address of WLAN clients are broadcasted in clear text even when WEP is implemented. Hacker can find the MAC addresses used in the WLAN. –Should be used as a feasible, but not as the sole security mechanism.

23. Wireless & Personal Communication Systems – CSE5807 Lecture: 10 23 Filtering Protocol Filtering: –WLAN can filter packets traversing the network based on layer 2-7 protocols. –Useful in controlling utilization of the shared medium.

24. Wireless & Personal Communication Systems – CSE5807 Lecture: 10 24 Emerging Wireless Security Solutions VPN 802.1x using Extensible Authentication Protocol (EAP). Temporal Key Integrity Protocol (TKIP) 802.11i Based on passing authentication through to authentication servers upstream from the access points. –Wireless client waiting during the authentication process.

25. Wireless & Personal Communication Systems – CSE5807 Lecture: 10 25 IEEE802.1x and EAP EAP is a layer 2 protocol. Ability to allow a connection into the network at layer 2 only if user authentication is successful. User authentication is accomplished using a Remote Authentication Dial-In User Service (RADIUS) server and some type of user database. AP Associate EAP Identity Request EAP Identity Response EAP Auth Request EAP-Success EAP Auth Response EAP Identity Response EAP Auth Response EAP Auth Request EAP-Success Authentication Server

26. Wireless & Personal Communication Systems – CSE5807 Lecture: 10 26 IEEE802.1x and EAP LEAP (Lightweight EAP) –Primarily used in Cisco wireless LAN access points. –Encryption using dynamically generated WEP keys and supports mutual authentication. EAP-TLS (EAP-Transport Layer Security) –Certificate based, mutual authentication of the client and the network. –Relies on client-side and server-side certificates to perform authentication. EAP-TTLS (EAP-Tunneled Transport Layer Security) –Extension of EAP-TLS. –Requires only server side certificates. PEAP (Protected EAP) –Developed by Cisco and Microsoft, as an alternative to EAP-TTLS. –Uses tunneled server-side certificates and username/password credentials for client to authenticate. –Supports mutual authentication.

27. Wireless & Personal Communication Systems – CSE5807 Lecture: 10 27 Temporal Key Integrity Protocol (TKIP) An upgrade to WEP that fixes known security problems in WEP’s implementation of the RC4 stream cipher. –IV hashing to help defeat packet snooping. –Message Integrity Check to determine unauthorized packet modification by injecting traffic. –Dynamic keys to defeat capture of passive keys. Firmware upgrades to access points and client devices.

28. Wireless & Personal Communication Systems – CSE5807 Lecture: 10 28 Temporal Key Integrity Protocol (TKIP) 128-bit temporal key shared amongst all clients and access points. –Temporal key is combined with a client’s MAC address and then added to a very large 16-octet IV to produce the actual encryption key. –RC4 is used for encryption. –Temporal key is changed over 10,000 packets (in every hour in many cases). Performance loss when using TKIP. –Trade-off with network security gain.

29. Wireless & Personal Communication Systems – CSE5807 Lecture: 10 29 IEEE802.11i Defines a new type of wireless network called a “Robust Security Network” (RSN). –IEEE802.1x and EAP –Advanced Encryption Standard (AES). TKIP is allowed as an optional mode in RSN. Wi-Fi Protected Access (WPA): –Wi-Fi Alliance adopted TKIP as a new security approach. –WPA is subset of RSN.

30. Wireless & Personal Communication Systems – CSE5807 Lecture: 10 30 References K. Pahlavan and K. Krishnamurthy “Principles of Wireless Networks”, Prentice-Hall, 2002. Hon Edney and William A. Arbaugh, “Real 802.11 Security: Wi-Fi Protected Access and 802.11i”, Pearson Education, 2004