1. CWNA Guide to Wireless LANs, Second Edition Chapter Eight Wireless LAN Security and Vulnerabilities

2. Objectives Define information security Explain the basic security protections for IEEE 802.11 WLANs List the vulnerabilities of the IEEE 802.11 standard Describe the types of wireless attacks that can be launched against a wireless network

3. Security Principles: What is Information Security? Information security: Task of guarding digital information –Ensures protective measures properly implemented –Protects confidentiality, integrity, and availability (CIA) on the devices that store, manipulate, and transmit the information through products, people, and procedures

4. Security Principles: What is Information Security? (continued) Information security components

5. Security Principles: Challenges of Securing Information Trends influencing increasing difficultly in information security: –Speed of attacks –Sophistication of attacks –Faster detection of weaknesses Day zero attacks –Distributed attacks The “many against one” approach Impossible to stop attack by trying to identify and block source

6. Security Principles: Categories of Attackers Six categories of attackers: –Hackers Not malicious; expose security flaws –Crackers –Script kiddies –Spies –Employees –Cyberterrorists

7. Security Principles: Categories of Attackers (continued) Attacker profiles

8. Security Principles: Security Organizations Many security organizations exist to provide security information, assistance, and training –Computer Emergency Response Team Coordination Center (CERT/CC) –Forum of Incident Response and Security Teams (FIRST) –InfraGard –Information Systems Security Association (ISSA) –National Security Institute (NSI) –SysAdmin, Audit, Network, Security (SANS) Institute

9. Basic IEEE 802.11 Security Protections Data transmitted by a WLAN could be intercepted and viewed by an attacker –Important that basic wireless security protections be built into WLANs Three categories of WLAN protections: –Access control –Wired equivalent privacy (WEP) –Authentication Some protections specified by IEEE, while others left to vendors

10. Access Control Intended to guard availability of information Wireless access control: Limit user’s admission to AP –Filtering Media Access Control (MAC) address filtering: Based on a node’s unique MAC address MAC address

11. Access Control (continued) MAC address filtering

12. Access Control (continued) MAC address filtering considered to be a basic means of controlling access –Requires pre-approved authentication –Difficult to provide temporary access for “guest” devices

13. Wired Equivalent Privacy (WEP) Guard the confidentiality of information –Ensure only authorized parties can view it Used in IEEE 802.11 to encrypt wireless transmissions –“Scrambling”

14. WEP: Cryptography Cryptography: Science of transforming information so that it is secure while being transmitted or stored –scrambles” data Encryption: Transforming plaintext to ciphertext Decryption: Transforming ciphertext to plaintext Cipher: An encryption algorithm –Given a key that is used to encrypt and decrypt messages –Weak keys: Keys that are easily discovered

15. WEP: Cryptography (continued) Cryptography

16. WEP: Implementation IEEE 802.11 cryptography objectives: –Efficient –Exportable –Optional –Reasonably strong –Self-synchronizing WEP relies on secret key “shared” between a wireless device and the AP –Same key installed on device and AP –Private key cryptography or symmetric encryption

17. WEP: Implementation (continued) Symmetric encryption

18. WEP: Implementation (continued) WEP shared secret keys must be at least 40 bits –Most vendors use 104 bits Options for creating WEP keys: –40-bit WEP shared secret key (5 ASCII characters or 10 hexadecimal characters) –104-bit WEP shared secret key (13 ASCII characters or 16 hexadecimal characters) –Passphrase (16 ASCII characters) APs and wireless devices can store up to four shared secret keys –Default key used for all encryption

19. WEP: Implementation (continued) Default WEP keys

20. WEP: Implementation (continued) WEP encryption process

21. WEP: Implementation (continued) When encrypted frame arrives at destination: –Receiving device separates IV from ciphertext –Combines IV with appropriate secret key Create a keystream –Keystream used to extract text and ICV –Text run through CRC Ensure ICVs match and nothing lost in transmission Generating keystream using the PRNG is based on the RC4 cipher algorithm –Stream Cipher

22. WEP: Implementation (continued) Stream cipher

23. Authentication IEEE 802.11 authentication: Process in which AP accepts or rejects a wireless device Open system authentication: –Wireless device sends association request frame to AP Carries info about supported data rates and service set identifier (SSID) –AP compares received SSID with the network SSID If they match, wireless device authenticated

24. Authentication (continued) Shared key authentication: Uses WEP keys –AP sends the wireless device the challenge text –Wireless device encrypts challenge text with its WEP key and returns it to the AP –AP decrypts returned result and compares to original challenge text If they match, device accepted into network

25. Vulnerabilities of IEEE 802.11 Security IEEE 802.11 standard’s security mechanisms for wireless networks have fallen short of their goal Vulnerabilities exist in: –Authentication –Address filtering –WEP

26. Open System Authentication Vulnerabilities Inherently weak –Based only on match of SSIDs –SSID beaconed from AP during passive scanning Easy to discover Vulnerabilities: –Beaconing SSID is default mode in all APs –Not all APs allow beaconing to be turned off Or manufacturer recommends against it –SSID initially transmitted in plaintext (unencrypted)

27. Open System Authentication Vulnerabilities (continued) Vulnerabilities (continued): –If an attacker cannot capture an initial negotiation process, can force one to occur –SSID can be retrieved from an authenticated device –Many users do not change default SSID Several wireless tools freely available that allow users with no advanced knowledge of wireless networks to capture SSIDs

28. Open System Authentication Vulnerabilities (continued) Forcing the renegotiation process

29. Shared Secret Key Authentication Vulnerabilities Attackers can view key on an approved wireless device (i.e., steal it), and then use on own wireless devices Brute force attack: Attacker attempts to create every possible key combination until correct key found Dictionary attack: Takes each word from a dictionary and encodes it in same way as passphrase –Compare encoded dictionary words against encrypted frame

30. Shared Secret Key Authentication Vulnerabilities (continued) AP sends challenge text in plaintext –Attacker can capture challenge text and device’s response (encrypted text and IV) Mathematically derive keystream

31. Shared Secret Key Authentication Vulnerabilities (continued) Table 8-2: Authentication attacks

32. Address Filtering Vulnerabilities MAC address attacks

33. WEP Vulnerabilities Uses 40 or 104 bit keys –Shorter keys easier to crack WEP implementation violates cardinal rule of cryptography –Creates detectable pattern for attackers –APs end up repeating IVs Collision: Two packets derived from same IV –Attacker can use info from collisions to initiate a keystream attack

34. WEP Vulnerabilities (continued) 8-13: XOR operations

35. WEP Vulnerabilities (continued) 8-14: Capturing packets

36. WEP Vulnerabilities (continued) PRNG does not create true random number –Pseudorandom –First 256 bytes of the RC4 cipher can be determined by bytes in the key itself WEP attacks

37. Other Wireless Attacks: Man-in-the- Middle Attack Makes it seem that two computers are communicating with each other –Actually sending and receiving data with computer between them –Active or passive Intercepting transmissions

38. Other Wireless Attacks: Man-in-the- Middle Attack (continued) Wireless man-in-the-middle attack

39. Other Wireless Attacks: Denial of Service (DoS) Attack Standard DoS attack attempts to make a server or other network device unavailable by flooding it with requests –Attacking computers programmed to request, but not respond Wireless DoS attacks are different: –Jamming: Prevents wireless devices from transmitting –Forcing a device to continually dissociate and re- associate with AP