Wireless%20Security%20(802.11b)

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Wireless Security (802.11b)

• Mahendran Velauthapillai
• April 29, 2004

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• Agenda
• Introduction to WLAN
• Communication Security Requirements
• 802.11b Security Architecture
• Security Issues in 802.11b
• Proposed Solutions for Enhanced Security

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Introduction to WLAN

• Two modes
• 1) Infrastructure
• 2) Adhoc

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Infrastructure Network
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Ad-Hoc Network

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• Prior to communicating data, wireless clients and
  access points must establish a relationship, or
  an association.
• Only after an association is established can the
• two wireless stations exchange data.

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Infrastructure Mode

• clients associate with an access point.
• The association process is a two step process
  involving three states
• 1. Unauthenticated and unassociated,
• 2. Authenticated and unassociated, and
• 3. Authenticated and associated.

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• To transition between the states, the
  communicating parties exchange messages called
  management frames.
• All access points transmit a beacon management
  frame at fixed interval.
• To associate with an access point and join a BSS,
  a client listens for beacon messages to identify
  the access points within range.
• The client then selects the BSS to join in a
  vendor independent manner.

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• A client may also send a probe request management
  frame to find an access point affiliated with a
  desired SSID.
• After identifying an access point, the client and
  the access point perform a mutual authentication
  by exchanging several management frames as part
  of the process.
• After successful authentication, the client moves
  into the second state, authenticated and
  unassociated.
• Moving from the second state to the third and
  final state, authenticated and associated,
  involves the client sending an association
  request frame, and the access point responding
  with an association response frame.

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Authentication Management Frame
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WEP
(encrypted traffic

• The industrys solution WEP (Wired Equivalent
  Privacy)
• Share a single cryptographic key among all
  devices
• Encrypt all packets sent over the air, using
  the shared key
• Use a checksum to prevent injection of spoofed
  packets

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Communication Security Requirements

• Privacy
• Data Integrity
• Authentication

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802.11b Security Architecture

• Link-layer security protocol
• Prevent link-layer eavesdropping
• Control network access
• WEP (Wired Equivalent Protocol)
• Essentially, equivalent to wired
• access point security

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WEP Requirements

• Reasonably Strong (What does this mean?)
• Self-synchronizing
• Computationally efficient
• Exportable
• Optional

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WEP Data Frame
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802.11b Shared Key Authentication
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Security Issues

• War Driving / Sniffing (Parking Lot attack)
• Rogue Access Points
• MAC Address
• SSID
• WEP

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War Driving

• War driving is one of the latest hacker fads
• http//www.wardriving.com/
• Involves driving around and scanning in search of
  unprotected 802.11 wireless networks
• Several War Driving tools are available
• NetStumbler
• AiroPeek
• MobileManager
• Sniffer Wireless
• THC-WarDrive

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War Driving Example
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Parking Lot Attack
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Unauthorized Access Points

• Install access points without permission
• (Bala!!!!! Shuuuu!)
• Security is NOT enabled
• The whole Network becomes vulnerable
• to war driving/sniffing attacks

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Using MAC Address

• Control access by allowing only valid
• MAC addresses to access the network
• Complicated and difficult to maintain list of
  valid MAC addresses
• Using software, MAC addresses can be spoofed

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Service Set ID (SSID)

• SSID is the network name given to a wireless
  network
• Can be used to access a specific access point by
  name
• The more people that come to know about the SSID
  the more likely that it will be misused
• Changes in SSID requires communicating it to all
  people who access the network

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Wired Equivalent Protocol (WEP)

• Not an industrial strength encryption protocol
• 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 share the same encryption key
• Data headers are not encrypted
• Initialization Vector (IV) Misuse
• Weakness in RC4s Key Scheduling Algorithm

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WEP - A Little More Detail
IV, P ? RC4(K, IV)

• WEP uses the RC4 stream cipher to encrypt a
  TCP/IPpacket (P) by xor-ing it with keystream
  (RC4(K, IV))

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A Property of RC4

• Keystream leaks, under known-plaintext attack
• Suppose we intercept a ciphertext C, and suppose
  we can guess the corresponding plaintext P
• Let Z RC4(K, IV) be the RC4 keystream
• Since C P ? Z, we can derive the RC4 keystream
  Z by P ? C P ? (P ? Z) Z
• This is not a problem ... unless keystream is
  reused!

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A Risk of Keystream Reuse

• If IVs repeat, confidentiality is at risk
• If we send two ciphertexts (C, C) using the same
  IV, then the xor of plaintexts leaks (P ? P C
  ? C), which might reveal both plaintexts
• ? Lesson If RC4 isnt used carefully, it becomes
  insecure

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A Risk With RC4

• If any IV ever repeats, confidentiality is at
  risk
• Suppose P, P are two plaintexts encrypted with
  same IV
• Let Z RC4(key, IV) then the two ciphertexts
  areC P ? Z and C P ? Z
• Note that C ? C P ? P,hence the xor of both
  plaintexts is revealed
• If there is redundancy, this may reveal both
  plaintexts
• Or, if we can guess one plaintext, the other is
  leaked
• So If RC4 isnt used carefully, it becomes
  insecure

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Attack 1 Keystream Reuse

• WEP didnt use RC4 carefully
• The problem IVs frequently repeat
• The IV is often a counter that starts at zero
• Hence, rebooting causes IV reuse
• Also, there are only 16 million possible IVs, so
  after intercepting enough packets, there are sure
  to be repeats
• ? Attackers can eavesdrop on 802.11 traffic
• An eavesdropper can decrypt intercepted
  ciphertexts even without knowing the key

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WEP -- Even More Detail
IV
original unencrypted packet
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Attack 2 Spoofed Packets

• Attackers can inject forged 802.11 traffic
• Learn RC4(K, IV) using previous attack
• Since the checksum is unkeyed, you can then
  create valid ciphertexts that will be accepted by
  the receiver
• ? Attackers can bypass 802.11 access control
• All computers attached to wireless net are
  exposed

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Attack 3 Reaction Attacks
P ? RC4(K)

• TCP ACKnowledgement appears ? TCP checksum on
  received (modified) packet is valid ? P
  0x0101 has exactly 1 bit set
• ? Attacker can recover plaintext (P) without
  breaking RC4

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Attacks on WEP

• Downloadable procedures
• To crack the key
• AirSnort http//airsnort.sourceforge.net/
• WEPCrack http//sourceforge.net/projects/wepcrack
  /
• To brute force enter into WLAN
• THC-RUT www.thehackerschoice.com/releases.php

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Proposed Solutions to Enhance Security

• Virtual Private Network (VPN)
• Secure LAN (SLAN)
• Remote Authentication Dial In User Services
  (RADIUS)
• IPsec
• 802.1x
• Proprietary WEP Implementations

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VPN

• Enables you to send data between two computers
  across a shared or public network in a manner
  that emulates the properties of a point-to-point
  private link
• 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

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(No Transcript)
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Secure LAN (SLAN)

• A GPL open-source VPN System
• 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
• Support for Windows and Linux
• Website http//slan.sourceforge.net/

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SLAN Architecture
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RADIUS

• Several 802.11 access points offer RADIUS
  authentication
• Clients can gain access to the network by
  supplying a username and password to a separate
  server
• This information is securely sent over the
  network eliminating the possibility of passive
  snooping

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IPsec

• Provides encryption and authentication services
  at the IP level of the network protocol stack
• Can be used to secure nearly any type of Internet
  traffic
• Legacy applications not implementing secure
  communications can be made secure using IPsec
• Examples
• Free S/WAN - http//www.freeswan.org/

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IPsec - Disadvantages

• IPsec authenticates machines, not users
• IPsec does not stop Denial-of-Service attacks
• IPsec is not true end-to-end security
• IPsec cannot be secure if your system isnt

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802.1x

• Provides enhanced security for users of 802.11b
  WLANs
• Provides port-level authentication for any wired
  or wireless Ethernet client system
• 802.1x was originally designed as a standard for
  wired Ethernet, but is applicable to WLANs
• It leverages many of the security features used
  with dial-up networking (RADIUS)
• Also uses Extensible Authentication Protocol
  (EAP, RFC 2284)
• Built in support in Windows XP

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802.1x Authentication
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Proprietary WEP Security

• Dynamic Key Refresh instead of static keys
• Use of 3DES/AES instead of RC4 (NetMotion
  Wireless)
• Disadvantages
• Interoperability Issues (non-WiFi Compliant)

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Conclusion

• Wireless LANs are very useful and convenient, but
  current security state not ideal for sensitive
  environments
• Care must be taken before sensitive information
  is made available over Wireless LANs