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Wireless LAN Security &
Vulnerabilities and
Implementing Wireless LAN Security
4DWN
Session 7
Objectives - Wireless LAN
Security & Vulnerabilities
• Define information security
• Explain the basic security protections for IEEE
802.11 WLANs
• List the vulnerabilities of the IEEE 802.11
standard
• Describe the types of wireless attacks that can
be launched against a wireless network
CWNA Guide to Wireless LANs, Second Edition 2
Objectives - Implementing
Wireless LAN Security
• List wireless security solutions
• Tell the components of the transitional security
model
• Describe the personal security model
• List the components that make up the enterprise
security model
CWNA Guide to Wireless LANs, Second Edition 3
Security Principles: What
is Information Security?
• Information security: Task of guarding digital
information
– Ensures protective measures properly implemented
– Protects confidentiality, integrity, and availability (CIA)
on the devices that store, manipulate, and transmit
the information through products, people, and
procedures
CWNA Guide to Wireless LANs, Second Edition 4
Security Principles: Challenges of
Securing Information
• Trends influencing increasing difficultly in
information security:
– Speed of attacks
– Sophistication of attacks
– Faster detection of weaknesses
• Day zero attacks
– Distributed attacks
• The “many against one” approach
• Impossible to stop attack by trying to identify and block
source
CWNA Guide to Wireless LANs, Second Edition 5
Security Principles: Categories
of Attackers
• Six categories of attackers:
– Hackers
• Not malicious; expose security flaws
– Crackers
– Script kiddies
– Spies
– Employees
– Cyberterrorists
CWNA Guide to Wireless LANs, Second Edition 6
Security Principles: Categories
of Attackers (continued)
Table 8-1: Attacker profiles
CWNA Guide to Wireless LANs, Second Edition 7
Security Principles:
Security Organizations
• Many security organizations exist to provide
security information, assistance, and training
– Computer Emergency Response Team Coordination
Center (CERT/CC)
– Forum of Incident Response and Security Teams
(FIRST)
– InfraGard
– Information Systems Security Association (ISSA)
– National Security Institute (NSI)
– SysAdmin, Audit, Network, Security (SANS) Institute
CWNA Guide to Wireless LANs, Second Edition 8
Basic IEEE 802.11 Security
Protections
• Data transmitted by a WLAN could be
intercepted and viewed by an attacker
– Important that basic wireless security protections be
built into WLANs
• Three categories of WLAN protections:
– Access control
– Wired equivalent privacy (WEP)
– Authentication
• Some protections specified by IEEE, while
others left to vendors
CWNA Guide to Wireless LANs, Second Edition 9
Access Control
• Intended to guard availability of information
• Wireless access control: Limit user’s
admission to AP
– Filtering
• Media Access Control (MAC) address
filtering: Based on a node’s unique MAC
address
Figure 8-2: MAC address
CWNA Guide to Wireless LANs, Second Edition 10
Access Control (continued)
Figure 8-4: MAC address filtering
CWNA Guide to Wireless LANs, Second Edition 11
Access Control (continued)
• MAC address filtering considered to be a basic
means of controlling access
– Requires pre-approved authentication
– Difficult to provide temporary access for “guest”
devices
CWNA Guide to Wireless LANs, Second Edition 12
Wired Equivalent Privacy
(WEP)
• Guard the confidentiality of information
– Ensure only authorized parties can view it
• Used in IEEE 802.11 to encrypt wireless
transmissions
– “Scrambling”
CWNA Guide to Wireless LANs, Second Edition 13
WEP: Cryptography
• Cryptography: Science of transforming information so
that it is secure while being transmitted or stored
– scrambles” data
• Encryption: Transforming plaintext to ciphertext
• Decryption: Transforming ciphertext to plaintext
• Cipher: An encryption algorithm
– Given a key that is used to encrypt and decrypt messages
– Weak keys: Keys that are easily discovered
CWNA Guide to Wireless LANs, Second Edition 14
WEP: Cryptography
Figure 8-5: Cryptography 15
WEP: Implementation
• IEEE 802.11 cryptography objectives:
– Efficient
– Exportable
– Optional
– Reasonably strong
– Self-synchronizing
• WEP relies on secret key “shared” between a
wireless device and the AP
– Same key installed on device and AP
– Private key cryptography or symmetric encryption
CWNA Guide to Wireless LANs, Second Edition 16
WEP: Implementation
Figure 8-6: Symmetric encryption 17
WEP: Implementation
• WEP shared secret keys must be at least 40 bits
– Most vendors use 104 bits
• Options for creating WEP keys:
– 40-bit WEP shared secret key (5 ASCII characters or
10 hexadecimal characters)
– 104-bit WEP shared secret key (13 ASCII characters
or 16 hexadecimal characters)
– Passphrase (16 ASCII characters)
• APs and wireless devices can store up to four
shared secret keys
– Default key used for all encryption
CWNA Guide to Wireless LANs, Second Edition 18
WEP: Implementation
Figure 8-8: Default WEP keys 19
WEP: Implementation
Figure 8-9: WEP encryption process
CWNA Guide to Wireless LANs, Second Edition 20
WEP: Implementation
• When encrypted frame arrives at destination:
– Receiving device separates IV from ciphertext
– Combines IV with appropriate secret key
• Create a keystream
– Keystream used to extract text and ICV
– Text run through CRC
• Ensure ICVs match and nothing lost in transmission
• Generating keystream using the PRNG is based
on the RC4 cipher algorithm
– Stream Cipher
CWNA Guide to Wireless LANs, Second Edition 21
WEP: Implementation
Figure 8-10: Stream cipher
CWNA Guide to Wireless LANs, Second Edition 22
Authentication
• IEEE 802.11 authentication: Process in which
AP accepts or rejects a wireless device
• Open system authentication:
– Wireless device sends association request frame to
AP
• Carries info about supported data rates and service set
identifier (SSID)
– AP compares received SSID with the network SSID
• If they match, wireless device authenticated
CWNA Guide to Wireless LANs, Second Edition 23
Authentication (continued)
• Shared key authentication: Uses WEP keys
– AP sends the wireless device the challenge text
– Wireless device encrypts challenge text with its WEP
key and returns it to the AP
– AP decrypts returned result and compares to original
challenge text
• If they match, device accepted into network
CWNA Guide to Wireless LANs, Second Edition 24
Vulnerabilities of IEEE
802.11 Security
• IEEE 802.11 standard’s security mechanisms for
wireless networks have fallen short of their goal
• Vulnerabilities exist in:
– Authentication
– Address filtering
– WEP
CWNA Guide to Wireless LANs, Second Edition 25
Open System Authentication
Vulnerabilities
• Inherently weak
– Based only on match of SSIDs
– SSID beaconed from AP during passive scanning
• Easy to discover
• Vulnerabilities:
– Beaconing SSID is default mode in all APs
– Not all APs allow beaconing to be turned off
• Or manufacturer recommends against it
– SSID initially transmitted in plaintext (unencrypted)
CWNA Guide to Wireless LANs, Second Edition 26
Open System Authentication
Vulnerabilities (continued)
• Vulnerabilities (continued):
– If an attacker cannot capture an initial negotiation
process, can force one to occur
– SSID can be retrieved from an authenticated device
– Many users do not change default SSID
• Several wireless tools freely available that allow
users with no advanced knowledge of wireless
networks to capture SSIDs
CWNA Guide to Wireless LANs, Second Edition 27
Open System Authentication
Vulnerabilities (continued)
Figure 8-12: Forcing the renegotiation process
28
Shared Secret Key
Authentication Vulnerabilities
• Attackers can view key on an approved wireless
device (i.e., steal it), and then use on own
wireless devices
• Brute force attack: Attacker attempts to create
every possible key combination until correct key
found
• Dictionary attack: Takes each word from a
dictionary and encodes it in same way as
passphrase
– Compare encoded dictionary words against encrypted
frame
29
Shared Secret Key Authentication
Vulnerabilities (continued)
• AP sends challenge text in plaintext
– Attacker can capture challenge text and device’s
response (encrypted text and IV)
• Mathematically derive keystream
CWNA Guide to Wireless LANs, Second Edition 30
Shared Secret Key
Authentication Vulnerabilities
Table 8-2: Authentication attacks 31
Address Filtering
Vulnerabilities
Table 8-3: MAC address attacks
CWNA Guide to Wireless LANs, Second Edition 32
WEP Vulnerabilities
• Uses 40 or 104 bit keys
– Shorter keys easier to crack
• WEP implementation violates cardinal rule of
cryptography
– Creates detectable pattern for attackers
– APs end up repeating IVs
• Collision: Two packets derived from same IV
– Attacker can use info from collisions to initiate a
keystream attack
CWNA Guide to Wireless LANs, Second Edition 33
WEP Vulnerabilities
Figure 8-13: XOR operations 34
WEP Vulnerabilities
(continued)
Figure 8-14: Capturing packets
CWNA Guide to Wireless LANs, Second Edition 35
WEP Vulnerabilities (continued)
• PRNG does not create true random number
– Pseudorandom
– First 256 bytes of the RC4 cipher can be determined
by bytes in the key itself
Table 8-4: WEP attacks
CWNA Guide to Wireless LANs, Second Edition 36
Other Wireless Attacks:
Man-in-the-Middle Attack
• Makes it seem that two computers are
communicating with each other
– Actually sending and receiving data with computer
between them
– Active or passive
Figure 8-15: Intercepting transmissions
CWNA Guide to Wireless LANs, Second Edition 37
Other Wireless Attacks: Man-
in-the-Middle Attack
38
Figure 8-16: Wireless man-in-the-middle attack
Other Wireless Attacks: Denial
of Service (DoS) Attack
• Standard DoS attack attempts to make a server
or other network device unavailable by flooding
it with requests
– Attacking computers programmed to request, but not
respond
• Wireless DoS attacks are different:
– Jamming: Prevents wireless devices from
transmitting
– Forcing a device to continually dissociate and re-
associate with AP
39
Wireless Security
Solutions
• IEEE 802.11a and 802.11b standards included
WEP specification
– Vulnerabilities quickly realized
– Organizations implemented “quick fixes”
• Did not adequately address encryption and authentication
• IEEE and Wi-Fi Alliance started working on
comprehensive solutions
– IEEE 802.11i and Wi-Fi Protected Access (WPA)
• Foundations of today’s wireless security
CWNA Guide to Wireless LANs, Second Edition 40
WEP2
• Attempted to overcome WEP limitations by
adding two new security enhancements
– WEP key increased to 128 bits
– Kerberos authentication
• User issued “ticket” by Kerberos server
• Presents ticket to network for a service
– Used to authenticate user
• No more secure than WEP
– Collisions still occur
– New dictionary-based attacks available
CWNA Guide to Wireless LANs, Second Edition 41
Dynamic WEP
• Solves weak IV problem by rotating keys
frequently
– More difficult to crack encrypted packet
• Uses different keys for unicast and broadcast
traffic
– Unicast WEP key unique to each user’s session
• Dynamically generated and changed frequently
– Broadcast WEP key must be same for all users on a
particular subnet and AP
CWNA Guide to Wireless LANs, Second Edition 42
Dynamic WEP (continued)
Figure 9-1: Dynamic WEP
CWNA Guide to Wireless LANs, Second Edition 43
Dynamic WEP (continued)
• Can be implemented without upgrading device
drivers or AP firmware
– No-cost and minimal effort to deploy
• Does not protect against man-in-the-middle
attacks
• Susceptible to DoS attacks
CWNA Guide to Wireless LANs, Second Edition 44
IEEE 802.11i
• Provides solid wireless security model
– Robust security network (RSN)
– Addresses both encryption and authentication
• Encryption accomplished by replacing RC4 with
a block cipher
– Manipulates entire block of plaintext at one time
• Block cipher used is Advanced Encryption
Standard (AES)
– Three step process
– Second step consists of multiple rounds of encryption
CWNA Guide to Wireless LANs, Second Edition 45
IEEE 802.11i (continued)
Table 9-1: Time needed to break AES
CWNA Guide to Wireless LANs, Second Edition 46
IEEE 802.11i (continued)
• IEEE 802.11i authentication and key
management is accomplished by IEEE 802.1x
standard
– Implements port security
• Blocks all traffic on port-by-port basis until client
authenticated using credentials stored on authentication
server
• Key-caching: Stores information from a device
on the network, for faster re-authentication
• Pre-authentication: Allows a device to become
authenticated to an AP before moving to it
CWNA Guide to Wireless LANs, Second Edition 47
IEEE 802.11i (continued)
Figure 9-2: IEEE 802.1x
CWNA Guide to Wireless LANs, Second Edition 48
Wi-Fi Protected Access (WPA)
Temporal Key Integrity Protocol (TKIP)
• TKIP was the first attempt to fix WEP security holes.
• Not perfect solution to 802.11’s security, but better
than WEP
• TKIP uses RC4 encryption, same as WEP
• WEP uses 64-bit & 128-bit keys, TKIP uses only
128-bit keys
• TKIP’s implementation of RC4 encryption is stronger
than WEP’s
• TKIP uses per-packet key mixing and automatic
rekeying
Wi-Fi Protected Access (WPA)
TKIP - Per Packet Key Mixing
• Each station is assigned a static WEP key
which is the same for all stations (same as
in WEP)
• This key is called the temporal key
• Each stations combines this key with its six-
byte MAC address to create an encryption
key that is unique for each station
Wi-Fi Protected Access (WPA)
TKIP - Per Packet Key Mixing
• TKIP also uses a six-byte IV instead of
WEP’s three-byte IV.
• This is known as Phase 1 intermediate key
• The second phase, the Phase 1
intermediate key is run through a simple
algorithm known as mixing algorithm to
produce the encryption key for the frame.
(makes it hard to determine if using WEP
or not)
Wi-Fi Protected Access (WPA)
TKIP - Automatic rekeying
• TKIP provides a mechanism whereby a station’s
temporal key can be periodically changed.
• This is performed every 10,000 frames
• Rekeying ensures that
–No station has a temporal key long enough to exhaust
the keystream associated with that key
–No station has a temporal key long enough for an
attacker to crack the key
–If an attacker does crack the key it is only good for the
balance of the current set of 10,000 frames
Wi-Fi Protected Access (WPA)
TKIP
• TKIP addresses replay attacks by
enforcing sequence number ordering on
frames
• TKIP addresses frame forgery through use
of a message integrity checksum (MIC)
• This is a small eight-byte additional
encryption method that detects if the frame
has been modified
Wi-Fi Protected Access
(continued)
Figure 9-3: Message Integrity Check (MIC)
CWNA Guide to Wireless LANs, Second Edition 54
Wi-Fi Protected Access 2
(WPA2)
• Second generation of WPA security
– Based on final IEEE 802.11i standard
– Uses AES for data encryption
– Supports IEEE 802.1x authentication or PSK
technology
– Allows both AES and TKIP clients to operate in same
WLAN
CWNA Guide to Wireless LANs, Second Edition 55
Summary of Wireless
Security Solutions
• Wi-Fi Alliance categorizes WPA and WPA2 by
modes that apply to personal use and to larger
enterprises
Figure 9-4: Security timeline
CWNA Guide to Wireless LANs, Second Edition 56
Summary of Wireless
Security Solutions (continued)
Table 9-2: Wi-Fi modes
Table 9-3: Wireless security solutions
CWNA Guide to Wireless LANs, Second Edition 57
Transitional Security Model
• Transitional wireless implementation
– Should be temporary
• Until migration to stronger wireless security possible
– Should implement basic level of security for a WLAN
• Including authentication and encryption
CWNA Guide to Wireless LANs, Second Edition 58
Authentication: Shared
Key Authentication
• First and perhaps most important step
– Uses WEP keys
• Networks that support multiple devices should
use all four keys
– Same key should not be designated as default on
each device
CWNA Guide to Wireless LANs, Second Edition 59
Authentication: SSID
Beaconing
• Turn off SSID beaconing by configuring APs to
not include it
– Beaconing the SSID is default mode for all APs
• Good practice to use cryptic SSID
– Should not provide any information to attackers
CWNA Guide to Wireless LANs, Second Edition 60
WEP Encryption
• Although vulnerabilities exist, should be turned
on if no other options for encryption are
available
– Use longest WEP key available
– May prevent script kiddies or “casual” eavesdroppers
from attacking
Table 9-4: Transitional security model 61
Personal Security Model
• Designed for single users or small office home
office (SOHO) settings
– Generally 10 or fewer wireless devices
• Two sections:
– WPA: Older equipment
– WPA2: Newer equipment
CWNA Guide to Wireless LANs, Second Edition 62
WPA Personal Security:
PSK Authentication
• Uses passphrase (PSK) that is manually entered
to generate the encryption key
– PSK used as seed for creating encryption keys
• Key must be created and entered in AP and also
on any wireless device (“shared”) prior to (“pre”)
the devices communicating with AP
CWNA Guide to Wireless LANs, Second Edition 63
WPA Personal Security:
TKIP Encryption
• TKIP is a substitute for WEP encryption
– Fits into WEP procedure with minimal change
• Device starts with two keys:
– 128-bit temporal key
– 64-bit MIC
• Three major components to address vulnerabilities:
– MIC
– IV sequence
– TKIP key mixing
• TKIP required in WPA
64
WPA Personal Security: TKIP
Encryption
65
Figure 9-7: TKIP/MIC process
WPA2 Personal Security:
PSK Authentication
• PSK intended for personal and SOHO users
without enterprise authentication server
– Provides strong degree of authentication protection
• PSK keys automatically changed (rekeyed) and
authenticated between devices after specified
period of time or after set number of packets
(10K) transmitted (rekey interval)
• Employs consistent method for creating keys
– Uses shared secret entered at AP and devices
• Random sequence of at least 20 characters or 24
hexadecimal digits
CWNA Guide to Wireless LANs, Second Edition 66
WPA2 Personal Security:
AES-CCMP Encryption
• WPA2 personal security model encryption
accomplished via AES
• AES-CCMP: Encryption protocol in 802.11i
– CCMP based on Counter Mode with CBC-MAC
(CCM) of AES encryption algorithm
– CCM provides data privacy
– CBC-MAC provides data integrity and authentication
• AES processes blocks of 128 bits
– Cipher key length can be 128, 192 and 256 bits
– Number of rounds can be 10, 12, and 14
CWNA Guide to Wireless LANs, Second Edition 67
WPA2 Personal Security:
AES-CCMP Encryption (continued)
• AES encryption/decryption computationally
intensive
– Better to perform in hardware
Table 9-5: Personal security model
68
Enterprise Security Model
• Most secure level of security that can be
achieved today for wireless LANs
– Designed for medium to large-size organizations
– Intended for setting with authentication server
• Like personal security model, divided into
sections for WPA and WPA2
• Additional security tools available to increase
network protection
CWNA Guide to Wireless LANs, Second Edition 69
WPA Enterprise Security:
IEEE 802.1x Authentication
• Uses port-based authentication mechanisms
• Network supporting 802.1x standard should
consist of three elements:
– Supplicant: Wireless device which requires secure
network access
– Authenticator: Intermediary device accepting
requests from supplicant
• Can be an AP or a switch
– Authentication Server: Accepts requests from
authenticator, grants or denies access
CWNA Guide to Wireless LANs, Second Edition 70
WPA Enterprise Security:
IEEE 802.1x
Authentication (continued)
Figure 9-8: 802.1x protocol
CWNA Guide to Wireless LANs, Second Edition 71
WPA Enterprise Security:
IEEE 802.1x Authentication
(continued)
• Supplicant is software on a client implementing
802.1x framework
• Authentication server stores list of names and
credentials of authorized users
– Remote Authentication Dial-In User Service
(RADIUS) typically used
• Allows user profiles to be maintained in central database that
all remote servers can share
CWNA Guide to Wireless LANs, Second Edition 72
WPA Enterprise Security:
IEEE 802.1x Authentication
• 802.1x based on Extensible Authentication
Protocol (EAP)
– Several variations:
• EAP-Transport Layer Security (EAP-TLS)
• Lightweight EAP (LEAP)
• EAP-Tunneled TLS (EAP-TTLS)
• Protected EAP (PEAP)
• Flexible Authentication via Secure Tunneling (FAST)
– Each maps to different types of user logons,
credentials, and databases used in authentication
CWNA Guide to Wireless LANs, Second Edition 73
WPA Enterprise Security:
TKIP Encryption
• TKIP is a “wrapper” around WEP
– Provides adequate encryption mechanism for WPA
enterprise security
– Dovetails into existing WEP mechanism
• Vulnerabilities may be exposed in the future
CWNA Guide to Wireless LANs, Second Edition 74
WPA2 Enterprise Security:
IEEE 802.1x Authentication
• Enterprise security model using WPA2 provides
most secure level of authentication and
encryption available on a WLAN
• IEEE 802.1x is strongest type of wireless
authentication currently available
• Wi-Fi Alliance certifies WPA and WPA2
enterprise products using EAP-TLS
– Other EAP types not tested, but should run a WPA or
WPA2 environment
CWNA Guide to Wireless LANs, Second Edition 75
WPA2 Enterprise Security:
AES-CCMP Encryption
• AES: Block cipher that uses same key for
encryption and decryption
– Bits encrypted in blocks of plaintext
• Calculated independently
– block size of 128 bits
– Three possible key lengths: 128, 192, and 256 bits
– WPA2/802.11i uses128-bit key length
– Includes four stages that make up one round
• Each round is iterated 10 times
CWNA Guide to Wireless LANs, Second Edition 76
WPA2 Enterprise Security:
AES-CCMP Encryption
(continued)
Table 9-6: Enterprise security model
CWNA Guide to Wireless LANs, Second Edition 77
Other Enterprise Security Tools:
Virtual Private Network (VPN)
• Virtual private network (VPN): Uses a public,
unsecured network as if it were private, secured
network
• Two common types:
– Remote-access VPN: User-to-LAN connection used
by remote users
– Site-to-site VPN: Multiple sites can connect to other
sites over Internet
• VPN transmissions are achieved through
communicating with endpoints
78
