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Security Issues with Wireless LANs

This article discusses the security vulnerabilities of wireless LANs, including the risks of hacking and the weaknesses of the Wired Equivalent Protocol (WEP). It also explains tools that can be used to hack wireless networks and highlights the importance of implementing encryption protection.

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Security Issues with Wireless LANs

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  1. Security Issues Raised by Wireless LANs Dr. John A. Copeland* Communications Systems Center Georgia Tech Electrical & Computer Engineering www.csc.gatech.edu copeland@ece.gatech.edu ECE6612 - Slide Set 14

  2. Network Tunnels Modems Internet VPNs Wireless Hubs 2

  3. Network Tunnels http://www.telecommagazine.com/default.asp?journalid=3&func=articles&page=0203t11&year=2002&month=3 3

  4. Network Tunnels Anyone can convert their cube or office Ethernet jack into a Wireless Hub for their Laptop (and a public entry point into the Network) IEEE 802.11b Wireless PC Card - $ 19.99 Linksys Etherfast Wireless AP + Cable/DSL Router with 4-Port Switch - $ 44.99 4

  5. [ The Atlanta Journal-Constitution: 3/31/02 ] Wireless systems are simple to hack Terrorists could use techniques to attack airliners By DON PLUMMER Atlanta Journal-Constitution Staff Writer (Bill Corbitt) sits in his car in the short-term parking lot at an airport eating a sandwich, a Pringles can balanced on the dashboard. After Corbitt left Hartsfield Airport, he located more than 100 wireless networks in an hour of driving around Atlanta. He did not actually break into any of them but later demonstrated how he could by intercepting signals from several wireless systems in use at The Atlanta Journal-Constitution. "Some of these people are even transmitting their names and the exact locations of the wireless portals,” Corbitt said, pointing out the identifiers as they appeared on the screen of his laptop. Of the 120 wireless systems located, only 32 had activated the encryption protection included with the wireless software. Bill Corbitt, Bulwarkz Defensive Solutions http://www.accessatlanta.com/ajc/news/0302/31wireless.html 5

  6. “Network Stumbler” - shows 802.11 Networks WEP ON No No Screen of laptop with Wireless LAN card

  7. “AiroPeek” maps out who’s talking to who 7

  8. Data sniffed off the air from non-WEP session. 8

  9. AirSnort - a tool for Cracking WEP Messages AirSnort is a wireless LAN (WLAN) tool which recovers encryption keys. AirSnort operates by passively monitoring transmissions, computing the encryption key when enough packets have been gathered. 802.11b, using the Wired Equivalent Protocol (WEP), is crippled with numerous security flaws. Most damning of these is the weakness described in " Weaknesses in the Key Scheduling Algorithm of RC4 " by Scott Fluhrer, Itsik Mantin and Adi Shamir. Adam Stubblefield was the first to implement this attack, but he has not made his software public. AirSnort, along with WEPCrack, which was released about the same time as AirSnort, are the first publicly available implementations of this attack. AirSnort requires approximately 5-10 million encrypted packets to be gathered. Once enough packets have been gathered, AirSnort can guess the encryption password in under a second. http://airsnort.sourceforge.net 9

  10. How Does “Wired Equivalent Protocol (WEP) Work” What’s wrong with it? 10

  11. Wired Equivalent Protocol “The Insecurity of 802.11, an analysis of the Wired Equivalent Privacy protocol”, Black Hat Briefings, 11 July, 2001, Ian Goldberg, Zero-Knowledge Systems, ian@zeroknowledge.com 9with Nikita Borisov and David Wagner, UC Berkeley). http://www.cypherpunks.ca/bh2001/index.html 11

  12. The One-Time Pad The most secure encryption technique is a “One-Time Pad,” if the Pad is truly random (in WEP it is not). WEP uses the RC4 encryption algorithm (with a 40 or 80 bit key) to generate a stream of random looking bits, Pi. These are XORed with the message bits, Mi, to produce the cyphertext bits, Ci Ci = Mi (+) Pi The receiver has the same key, and can generate a duplicate “pad”, Pi, and recover the original plaintext message, Mi. Ci (+) Pi = Mi (+) Pi (+) Pi = Mi since Pi (+) Pi = 1 and Mi (+) 1 = Mi 12

  13. “Two-Time” Pad Problem The least secure encryption technique is a “One-Time Pad” - used twice (or repeatedly). Consider two intercepted messages (C and D are encrypted M and N) encrypted with the same pad: C = M (+) P and D = N (+) P The cracker can XOR these together to get M (+) N: C (+) D = M (+) P (+) N (+) P = M (+) N Whenever a byte in M (+) N is zero, M & N have the same byte. One of six bytes in English text is “space”. so one in 36 bytes in M+N is zero because both text strings have spaces there. Given several thousand characters of M+N, the messages can be deciphered. Then the key sequence can be found: P = N (+) D. 13

  14. “Two-Time” Pad Problem The pad, or keystream, for WEP is RC4(v,k) which depends only on v and k. “k” is a shared secret that changes rarely, if ever (in most systems (like GTwireless) every user uses the same value of k). So the keystream depends only on the 24-bit value of v. Since v is transmitted in the clear, the Cracker collects messages until he has two with the same value of v, then he is “in.” There are 2^24 = 16 million different values of v, but because of the “Birthday Effect,” he is likely to have two that match after collecting only about 6,000 messages. Number of different pairs = 6000 x 5999 / 2 Even worse, Goldberg reports that all the 802.11 cards observed reset their random number generator for v each time they are activated, meaning they reuse the same sequence of v values (2002). 14

  15. Defense These help WEP, but are not totally dependable: Use the 112-bit key mode, rather than no key or 56-bit key. Use an access list of MAC (Ethernet) addresses at the hub. Use a new hub that has WPA (22+ random-character passphrase), or IEEE 802.11i, and only network cards that are fully compatible. 15

  16. Wi-Fi Protected Access (WPA upgrades WEP) IEEE 802.1x authentication is required. TKIP encryption is used (unique unicast key) 8-bit “Michael” Message Integrity Check (MIC) Frame counter prevents replay attacks AES is optional. Some card CPU’s can not manage. Can support older WEP cards (but no dynamic keys) 802.11 Beacon Frames contain a WEP info element. WPA is currently supported by Windows XP and Apple 16

  17. WPA vs. WEP Minimum key length increased from 40 to 256 bits (four keys made from 8 to 63 character passcode). IV (Initial Vector) length was doubled. IV resequencing enforced. Key rotation embedded automatically. Mutual authentication required. MIC to prevent packet tampering. Attack code("coWEPtty") can crack passcode "abc123abc123" in less than a minute.* Longer (>22 characters) and more random codes are reasonable secure.** *H. Berghel, J. Uecker, WiFi Attack Vectors", Comm. ACM, pp 21-28, Aug. 2005. ** R. Moskowitz,http://wifinetnews.com/archives/002452.html 17

  18. 802.11x, EAP and LEAP IEEE 802.11x defines a structure for authenticated layer-2 access to any IEEE 802 network (3 - party). EAP (extensible authentication protocol) allows supplicant (client) to exchange credentials with the AS (authentication server). LEAP (lightweight EAP) available on Cisco and some Linksys access points. Most popular EAP, and flawed by use of MS-CHAPv2 (NT hashing does not use salt). Attack code "asleap" can discover LEAP passwords using an offline dictionary attack.* * H. Berghel, J. Uecker, "WiFi Attack Vectors", Comm. ACM, pp 21-28, Aug. 2005 18

  19. Defense - Higher Level Secure Protocols Process Process Application Application SSL SSL Router Transport Transport Buffers Packets that Layer Layer need to be forwarded (TCP,UDP) (TCP,UDP) (based on IP address). Network Network Layer (IP) Layer (IP) IPsec Network Network IPsec Layer Layer 802.11 Link Layer Ethernet Ethernet 802.11 802.11 Data Link Layer Link Layer Data-Link Layer Phys. Layer WEP WEP Ethernet Ethernet Phys. Layer 802.11 Phys. Layer Phys. Layer 19

  20. Defense - War Driving Patrol the Premises Frequently looking for Rogue Wireless Signals Purchase only 802.11 Hubs and PC Cards that have the improved Security standards, or flash memory and can be field upgraded. Treat all wireless communication channels as "public." Use only secure protocols: VPN, Radius, SSH, SSL, … . 20

  21. Wireless Sub-Nets can Safely be part of Corporate Networks - if Properly Isolated IDS Wireless Subnets should be treated like attachments to the Web, isolated by Firewalls and Intrusion Detection Systems Wireless Hub 21

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