Wireless LAN Security

Mandy Andress

ArcSec Technologies

Black Hat Briefings

July 12, 2001

Agenda

• Uses
• Benefits
• Standards
• Functionality
• Security Issues
• Solutions and Implementations

Uses

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

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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

Standards

• IEEE 802.11
• IEEE 802.11b
• IEEE 802.11a
• IEEE 802.11e
• HiperLAN/2
• Interoperability

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

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

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

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

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

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

Functionality

• Basic Configuration
• WLAN Communication
• WLAN Packet Structure

Basic Configuration

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

Hidden Node Problem

Four-Way Handshake

Source

Destination

RTS – Request to Send

CTS – Clear to Send

DATA

ACK

OSI Model

Application

Presentation

Session

Transport

Network

Data Link

Physical

802.11b

802.11 MAC header

802.11 PLCP header

Ethernet Packet Structure

Graphic Source: Network Computing Magazine August 7, 2000

• 14 byte header
• 2 addresses

802.11 Packet Structure

Graphic Source: Network Computing Magazine August 7, 2000

• 30 byte header
• 4 addresses

Ethernet Physical Layer Packet Structure

• 8 byte header (Preamble)

Graphic Source: Network Computing Magazine August 7, 2000

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

Security Issues and Solutions

• Sniffing and War Driving
• Rogue Networks
• Policy Management
• MAC Address
• SSID
• WEP

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.

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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

Policy Management

• Access is binary
• Full network access or no network access
• Need means of identifying and enforcing access policies

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

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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

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

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

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.

Basic WLAN Architecture

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

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

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

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

Intermediate WLAN Architecture

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

VPN Architecture

VPN Architecture

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

VLAN Architecture

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

Gateway Architecture

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

802.1x (cont)

• Could be implemented as early as 2002.
• Cisco Aironet 350 supports the draft standard.
• Microsoft includes support in Windows XP

802.1x Architecture

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

Client Considerations

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

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

Contact Information

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