Wireless LAN 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

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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

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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

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Hidden Node Problem
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Four-Way Handshake
Source
Destination
RTS Request to Send
CTS Clear to Send
DATA
ACK
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OSI Model
Application
Presentation
Session
Transport
Network
Data Link
802.11 MAC header
802.11b
Physical
802.11 PLCP header
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Ethernet Packet Structure

• 14 byte header
• 2 addresses

Graphic Source Network Computing Magazine August
7, 2000
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802.11 Packet Structure

• 30 byte header
• 4 addresses

Graphic Source Network Computing Magazine August
7, 2000
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Ethernet Physical Layer Packet Structure

• 8 byte header (Preamble)

Graphic Source Network Computing Magazine August
7, 2000
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802.11 Physical Layer Packet Structure

• 24 byte header (PLCP, Physical Layer Convergence
  Protocol)
• Always transferred at 1 Mbps

Graphic Source Network Computing Magazine August
7, 2000
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

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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

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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 days 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

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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.

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Basic WLAN Architecture
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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)

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

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Intermediate WLAN Architecture
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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

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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
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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 users IP address to the
  allowed list to provide network access

45
Gateway Architecture
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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

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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
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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 cards connection.
• Fortress Wireless Link Layer Security (WLLS).
  Improves WEP and works with 802.1x.
• Enterasys provides proprietary RADIUS solution
  similar to 802.1x

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Client Considerations

• Cannot forget client security
• Distributed Personal Firewalls
• Strong end user security policies and
  configurations
• Laptop Theft Controls

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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

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Contact Information

• Mandy_at_arcsec.com
• Presentation available for download at
  www.arcsec.com and www.survivingsecurity.com