Wireless Personal Communications Systems – CSE5807

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 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 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 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. x Encrypted Message (Cipher-text) Message (Plaintext/Clear-text) Y=Ek(X) Encryption Encrypted Message Message M=Dk(Y)=X Decryption Y 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.

6. Y Insecure Channel X X Decryption Encryption k k Secure Channel Y=Ek(X) : Ciphertext X=Dk(Y) : Plaintext Secret-Key/Symmetric Key Encryption • Sharing a secret key for encryption and decryption. • Advantage: Fast and suitable for high data rates. • Disadvantage: Secret key distribution. • Examples: • Data Encryption Standard (DES) • Advanced Encryption Standard (AES) • RC-4

7. Y Insecure Channel X X Decryption Encryption Kpub, A Kpri, A Y=Ekpub(X) : Ciphertext X=Dkpri(Y) : Plaintext 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.

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. 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. Authentication Request Frame LAN AP Authentication Response Frame 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.

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

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. Wired Equivalent Privacy (WEP)

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 (224) 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. Associate EAP Identity Response EAP Auth Response AP EAP Identity Request EAP Auth Request EAP-Success EAP Identity Response EAP Auth Response EAP Auth Request EAP-Success 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. Authentication Server

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. 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. 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. 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. 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