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

2. CWNA Guide to Wireless LANs, Second EditionCCRI J. Bernardini 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. CWNA Guide to Wireless LANs, Second EditionCCRI J. Bernardini 3 Security Principles: What is Information Security? Information security: Task of guarding digital information Information must be protective - on the devices that store, manipulate, and transmit the information through products, people, and procedures. Information that must be protected are CIA Confidentiality –Only authorized parties can view information Integrity –Information is correct and unaltered Availability –Authorized parties must be able to access at all times

4. CWNA Guide to Wireless LANs, Second EditionCCRI J. Bernardini 4 Security Principles: What is Information Security?

5. CWNA Guide to Wireless LANs, Second EditionCCRI J. Bernardini 5 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. CWNA Guide to Wireless LANs, Second EditionCCRI J. Bernardini 6 Categories of Attackers Six categories of attackers: Hackers - Not malicious; expose security flaws, “ethical attackers” Crackers – Violates system security with malicious intent Script kiddies- Break into computers to create damage Spies – Hired to break in and steal information Employees- Unhappy employees that steal, damage and change information Cyber-terrorists- Steal, damage and change information for ideology or extreme beliefs

7. CWNA Guide to Wireless LANs, Second EditionCCRI J. Bernardini 7 Security Attackers Profiles

8. CWNA Guide to Wireless LANs, Second EditionCCRI J. Bernardini 8 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. CWNA Guide to Wireless LANs, Second EditionCCRI J. Bernardini 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. CWNA Guide to Wireless LANs, Second EditionCCRI J. Bernardini 10 Access Control Security Intended to guard one of the CIA’s –Availability of information Wireless access control: Limit user’s access to AP –by Filtering MAC addresses Media Access Control (MAC) address filtering: Based on a node’s unique MAC address Can be defeated by Spoofing a MAC address

11. CWNA Guide to Wireless LANs, Second EditionCCRI J. Bernardini 11 Access Control Filtering MAC address filtering considered to be a basic means of controlling access –Requires pre-approved authentication –Difficult to provide temporary access for “guest” devices

12. CWNA Guide to Wireless LANs, Second EditionCCRI J. Bernardini 12 Wired Equivalent Privacy (WEP) Guard the Confidentiality of CIA –Ensure only authorized parties can view it Used in IEEE 802.11 to encrypt wireless transmissions –“Scrambling 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

13. CWNA Guide to Wireless LANs, Second EditionCCRI J. Bernardini 13 WEP Cryptography

14. CWNA Guide to Wireless LANs, Second EditionCCRI J. Bernardini 14 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 A form of Private key cryptography or symmetric encryption

15. CWNA Guide to Wireless LANs, Second EditionCCRI J. Bernardini 15 WEP Symmetric Encryption

16. CWNA Guide to Wireless LANs, Second EditionCCRI J. Bernardini 16 WEP Characteristics 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 one of the four stored keys –Default key used for all encryption –Default key can be different for AP and client

17. CWNA Guide to Wireless LANs, Second EditionCCRI J. Bernardini 17 WEP Keys - Key order must be the same for all devices - Default Keys can be different for each device

18. CWNA Guide to Wireless LANs, Second EditionCCRI J. Bernardini 18 WEP Encryption Process Step-1 CRC ( Text) = ICV –CRC= Cyclic Redundancy Check ICV = Integrity Check Value IV = Initialization Vector 24-bit changes for each encryption Step-2 IV + Secrete Key =“seed” PRNG = Pseudo-Random Number Step-3 PRNG (seed) = “Keystream” Step-4 (Text+ICV) XOR (Keystream) =Ciphertext Step-5 IV + Ciphertext = Transmission A B XOR 0 0 0 1 0 1 0 1 1 1 1 0

19. CWNA Guide to Wireless LANs, Second EditionCCRI J. Bernardini 19 WEP Stream Cipher 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

20. CWNA Guide to Wireless LANs, Second EditionCCRI J. Bernardini 20 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 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

21. CWNA Guide to Wireless LANs, Second EditionCCRI J. Bernardini 21 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

22. CWNA Guide to Wireless LANs, Second EditionCCRI J. Bernardini 22 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) Vulnerabilities -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

23. CWNA Guide to Wireless LANs, Second EditionCCRI J. Bernardini 23 Open System Authentication Vulnerabilities (continued)

24. CWNA Guide to Wireless LANs, Second EditionCCRI J. Bernardini 24 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 AP sends challenge text in plaintext –Attacker can capture challenge text and device’s response (encrypted text and IV) Mathematically derive keystream

25. CWNA Guide to Wireless LANs, Second EditionCCRI J. Bernardini 25 Shared Secret Key Attacks

26. CWNA Guide to Wireless LANs, Second EditionCCRI J. Bernardini 26 Address Filtering Vulnerabilities

27. CWNA Guide to Wireless LANs, Second EditionCCRI J. Bernardini 27 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

28. CWNA Guide to Wireless LANs, Second EditionCCRI J. Bernardini 28 WEP XOR Operation

29. CWNA Guide to Wireless LANs, Second EditionCCRI J. Bernardini 29 Capturing packets

30. CWNA Guide to Wireless LANs, Second EditionCCRI J. Bernardini 30 WEP Attacks PRNG does not create true random number –Pseudorandom –First 256 bytes of the RC4 cipher can be determined by bytes in the key itself

31. CWNA Guide to Wireless LANs, Second EditionCCRI J. Bernardini 31 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

32. CWNA Guide to Wireless LANs, Second EditionCCRI J. Bernardini 32 Other Wireless Attacks: Man-in-the- Middle Attack (continued) Figure 8-16: Wireless man-in-the-middle attack

33. CWNA Guide to Wireless LANs, Second EditionCCRI J. Bernardini 33 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

34. CWNA Guide to Wireless LANs, Second EditionCCRI J. Bernardini 34 Summary Information security protects the confidentiality, integrity, and availability of information on the devices that store, manipulate, and transmit the information through products, people, and procedures Significant challenges in keeping wireless networks and devices secure Six categories of attackers: Hackers, crackers, script kiddies, computer spies, employees, and cyberterrorists

35. CWNA Guide to Wireless LANs, Second EditionCCRI J. Bernardini 35 Summary (continued) Three categories of default wireless protection: access control, wired equivalent privacy (WEP), and authentication Significant security vulnerabilities exist in the IEEE 802.11 security mechanisms Man-in-the-middle attacks and denial of service attacks (DoS) can be used to attack wireless networks