This document discusses security issues and solutions for wireless LANs. It begins by covering the standards, functionality, and uses of wireless LAN technology. It then outlines several security issues like sniffing, rogue networks, and vulnerabilities in the Wired Equivalent Privacy (WEP) protocol. Finally, it proposes some solutions for small, intermediate, and enterprise wireless network implementations including the use of VPNs, VLANs, custom authentication gateways, and the emerging 802.1x standard. The growing popularity of wireless LANs is increasing the need for improved security.

1. Wireless LAN Security
Mandy Andress
ArcSec Technologies
Black Hat Briefings
July 12, 2001

2. Agenda
 Uses
 Benefits
 Standards
 Functionality
 Security Issues
 Solutions and Implementations

3. Uses
 Key drivers are mobility and accessibility
 Easily change work locations in the office
 Internet access at airports, cafes, conferences,
etc.

4. Benefits
 Increased productivity
– Improved collaboration
– No need to reconnect to the network
– Ability to work in more areas
 Reduced costs
– No need to wire hard-to-reach areas

5. Standards
 IEEE 802.11
 IEEE 802.11b
 IEEE 802.11a
 IEEE 802.11e
 HiperLAN/2
 Interoperability

6. 802.11
 Published in June 1997
 2.4GHz operating frequency
 1 to 2 Mbps throughput
 Can choose between frequency hopping or
direct sequence spread modulation

7. 802.11b
 Published in late 1999 as supplement to
802.11
 Still operates in 2.4GHz band
 Data rates can be as high as 11 Mbps
 Only direct sequence modulation is specified
 Most widely deployed today

8. 802.11a
 Also published in late 1999 as a supplement to 802.11
 Operates in 5GHz band (less RF interference than
2.4GHz range)
 Users Orthogonal Frequency Division Multiplexing
(OFDM)
 Supports data rates up to 54 Mbps
 Currently no products available, expected in fourth
quarter

9. 802.11e
 Currently under development
 Working to improve security issues
 Extensions to MAC layer, longer keys, and key
management systems
 Adds 128-bit AES encryption

10. HiperLAN/2
 Development led by the European
Telecommunications Standards Institute (ETSI)
 Operates in the 5 GHz range, uses OFDM
technology, and support data rates over
50Mbps like 802.11a

11. Interoperability
 802.11a and 802.11b work on different
frequencies, so little chance for interoperability
 Can coexist in one network
 HiperLAN/2 is not interoperable with 802.11a
or 802.11b

12. Functionality
 Basic Configuration
 WLAN Communication
 WLAN Packet Structure

13. Basic Configuration

14. 802.11 Communication
 CSMA/CA (Carrier Sense Multiple
Access/Collision Avoidance) instead of
Collision Detection
 WLAN adapter cannot send and receive traffic
at the same time on the same channel
 Hidden Node Problem
 Four-Way Handshake

15. Hidden Node Problem

16. Four-Way Handshake
Source Destination

17. OSI Model
Application
Presentation
Session
Transport
Network
Data Link
Physical
802.11b
802.11 MAC header
802.11 PLCP header

18. Ethernet Packet Structure
Graphic Source: Network Computing Magazine August 7, 2000
•14 byte header
•2 addresses

19. 802.11 Packet Structure
Graphic Source: Network Computing Magazine August 7, 2000
•30 byte header
•4 addresses

20. Ethernet Physical Layer Packet
Structure
•8 byte header (Preamble)
Graphic Source: Network Computing Magazine August 7, 2000

21. 802.11 Physical Layer Packet
Structure
Graphic Source: Network Computing Magazine August 7, 2000
•24 byte header (PLCP, Physical Layer Convergence Protocol)
•Always transferred at 1 Mbps

22. Security Issues and Solutions
 Sniffing and War Driving
 Rogue Networks
 Policy Management
 MAC Address
 SSID
 WEP

23. War Driving
 Default installation allow any wireless NIC to
access the network
 Drive around (or walk) and gain access to
wireless networks
 Provides direct access behind the firewall
 Heard reports of an 8 mile range using a 24dB
gain parabolic dish antenna.

24. Rogue Networks
 Network users often set up rogue wireless
LANs to simplify their lives
 Rarely implement security measures
 Network is vulnerable to War Driving and
sniffing and you may not even know it

25. Policy Management
 Access is binary
 Full network access or no network access
 Need means of identifying and enforcing
access policies

26. MAC Address
 Can control access by allowing only defined
MAC addresses to connect to the network
 This address can be spoofed
 Must compile, maintain, and distribute a list of
valid MAC addresses to each access point
 Not a valid solution for public applications

27. Service Set ID (SSID)
 SSID is the network name for a wireless network
 WLAN products common defaults: “101” for 3COM and
“tsunami” for Cisco
 Can be required to specifically request the access
point by name (lets SSID act as a password)
 The more people that know the SSID, the higher the
likelihood it will be misused.
 Changing the SSID requires communicating the
change to all users of the network

28. Wired Equivalent Privacy (WEP)
 Designed to be computationally efficient, self-
synchronizing, and exportable
 Vulnerable to attack
– Passive attacks to decrypt traffic based on statistical analysis
– Active attacks to inject new traffic from unauthorized mobile
stations, based on known plaintext
– Dictionary-building attack that, after analysis of a day’s worth
of traffic, allows real-time automated decryption of all traffic
 All users of a given access point share the same
encryption key
 Data headers remain unencrypted so anyone can see
the source and destination of the data stream

29. WLAN Implementations
 Varies due to organization size and security
concerns
 Current technology not ideal for large-scale
deployment and management
 Will discuss a few tricks that can help the
process and a few technologies under
development to ease enterprise deployments

30. Basic WLAN
 Great for small (5-10 users) environments
 Use WEP (some vendors provide 128-bit
proprietary solution)
 Only allow specific MAC addresses to access
the network
 Rotate SSID and WEP keys every 30-60 days
 No need to purchase additional hardware or
software.

31. Basic WLAN Architecture

32. Secure LAN (SLAN)
 Intent to protect link between wireless client and
(assumed) more secure wired network
 Similar to a VPN and provides server authentication,
client authentication, data privacy, and integrity using
per session and per user short life keys
 Simpler and more cost efficient than a VPN
 Cross-platform support and interoperability, not highly
scaleable, though
 Supports Linux and Windows
 Open Source (slan.sourceforge.net)

33. SLAN Architecture

34. SLAN Steps
1. Client/Server Version Handshake
2. Diffie-Hellman Key Exchange
3. Server Authentication (public key fingerprint)
4. Client Authentication (optional) with PAM on
Linux
5. IP Configuration – IP address pool and adjust
routing table

35. SLAN Client
SLAN Driver
User Space Process
Physical Driver
Client Application
ie Web Browser
Plaintext Traffic
Plaintext
Traffic Encrypted Traffic
Encrypted Traffic to
SLAN Server
Encrypted Traffic

36. Intermediate WLAN
 11-100 users
 Can use MAC addresses, WEP and rotate
keys if you want.
 Some vendors have limited MAC storage
ability
 SLAN also an option
 Another solution is to tunnel traffic through a
VPN

37. Intermediate WLAN Architecture

38. VPN
 Provides a scaleable authentication and
encryption solution
 Does require end user configuration and a
strong knowledge of VPN technology
 Users must re-authenticate if roaming between
VPN servers

39. VPN Architecture

40. VPN Architecture

41. Enterprise WLAN
 100+ users
 Reconfiguring WEP keys not feasible
 Multiple access points and subnets
 Possible solutions include VLANs, VPNs,
custom solutions, and 802.1x

42. VLANs
 Combine wireless networks on one VLAN
segment, even geographically separated
networks.
 Use 802.1Q VLAN tagging to create a wireless
subnet and a VPN gateway for authentication
and encryption

43. VLAN Architecture

44. Customized Gateway
 Georgia Institute of Technology
 Allows students with laptops to log on to the campus
network
 Uses VLANs, IP Tables, and a Web browser
 No end user configuration required
– User access a web site and enters a userid and password
– Gateway runs specialized code authenticating the user with
Kerberos and packet filtering with IPTables, adding the user’s
IP address to the allowed list to provide network access

45. Gateway Architecture

46. 802.1x
 General-purpose port based network access control
mechanism for 802 technologies
 Based on AAA infrastructure (RADIUS)
 Also uses Extensible Authentication Protocol (EAP,
RFC 2284)
 Can provide dynamic encryption key exchange,
eliminating some of the issues with WEP
 Roaming is transparent to the end user

47. 802.1x (cont)
 Could be implemented as early as 2002.
 Cisco Aironet 350 supports the draft standard.
 Microsoft includes support in Windows XP

48. 802.1x Architecture

49. Third-Party Products
 NetMotion Wireless authenticates against a
Windows domain and uses better encryption
(3DES) than WEP. Also offers the ability to
remotely disable a wireless network card’s
connection.
 Fortress Wireless Link Layer Security (WLLS).
Improves WEP and works with 802.1x.
 Enterasys provides proprietary RADIUS
solution similar to 802.1x

50. Client Considerations
 Cannot forget client security
 Distributed Personal Firewalls
 Strong end user security policies and
configurations
 Laptop Theft Controls

51. Conclusion
 Wireless LANs very useful and convenient, but
current security state not ideal for sensitive
environments.
 Cahners In-Stat group predicts the market for
wireless LANs will be $2.2 billion in 2004, up
from $771 million in 2000.
 Growing use and popularity require increased
focus on security

52. Contact Information
 Mandy@arcsec.com
 Presentation available for download at
www.arcsec.com and
www.survivingsecurity.com