CWSP Guide to Wireless Security
Chapter 5
Wireless Security Models
Objectives
• Explain the advantages of WPA and WPA2
• Explain the technologies that are part of the personal
security model
• List the features of the transitional security model
• Define the enterprise security model
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Wireless Security Solutions
• WEP suffers from serious weakness
• “Band-aid” solutions
– WEP2 and Dynamic WEP
• Better solutions
– IEEE 802.11i
– Wi-Fi Protected Access (WPA)
– Wi-Fi Protected Access 2 (WPA2)
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IEEE 802.11i
• Addresses the two weaknesses of wireless
networks: encryption and authentication
• Encryption
– Replaces the RC4 stream cipher algorithm with a
block cipher
• Manipulates an entire block of text at one time
– 802.11i uses the Advanced Encryption Standard
(AES)
• Designed to be an encryption technique that is secure
from attacks
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IEEE 802.11i (continued)
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IEEE 802.11i (continued)
• Authentication and key management
– Accomplished by the IEEE 802.1x standard
• Implements port security
• Blocks all traffic on a port-by-port basis
– Until the client is authenticated using credentials
stored on an authentication server
• Key-caching
– Stores information from a device on the network
– If a user roams away and later returns
• She does not need to re-enter all of the credentials
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IEEE 802.11i (continued)
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IEEE 802.11i (continued)
• Pre-authentication
– Allows a device to become authenticated to an AP
• Before moving into range of the AP
– Device sends a pre-authentication packet to the AP
the user is currently associated with
• And the packet is then routed to a remote AP or APs
– Allows for faster roaming between access points
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Wi-Fi Protected Access (WPA)
• Subset of 802.11i and addresses both encryption
and authentication
• Temporal Key Integrity Protocol (TKIP)
– TKIP keys are known as per-packet keys
– TKIP dynamically generates a new key for each
packet that is created
– Prevent collisions
• Which was one of the primary weaknesses of WEP
• Authentication server can use 802.1x to produce a
unique master key for that user session
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Wi-Fi Protected Access (WPA)
(continued)
• TKIP distributes the key to wireless devices and AP
– Setting up an automated key hierarchy and
management system
• WPA replaces the Cyclic Redundancy Check (CRC)
with the Message Integrity Check (MIC)
– Designed to prevent an attacker from capturing,
altering, and resending data packets
– Provides a strong mathematical function
– Clients are de-authenticated and new associations are
prevented for one minute if an MIC error occurs
• Optional feature
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Wi-Fi Protected Access (WPA)
(continued)
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Wi-Fi Protected Access (WPA)
(continued)
• WPA authentication
– Accomplished by using either IEEE 802.1x or
preshared key (PSK) technology
• PSK authentication uses a passphrase to generate
the encryption key
– Passphrase must be entered on each access point
and wireless device in advance
– Serves as the seed for mathematically generating the
encryption keys
• WPA was designed to address WEP vulnerabilities
with minimum inconvenience
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Wi-Fi Protected Access 2 (WPA2)
• Second generation of WPA security
• Based on the final IEEE 802.11i standard
• Uses the Advanced Encryption Standard (AES) for
data encryption
• Supports IEEE 802.1x authentication or PSK
technology
• WPA2 allows both AES and TKIP clients to operate
in the same WLAN
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Wi-Fi Protected Access 2 (WPA2)
(continued)
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Wi-Fi Protected Access 2 (WPA2)
(continued)
• Wi-Fi Alliance wireless security models based on
WPA and WPA2
–
–
–
–
WPA—Personal Security
WPA—Enterprise Security
WPA2—Personal Security
WPA2—Enterprise Security
• Transitional security model
– Used as a “bridge” solution in situations where WPA or
WPA2 security is not available
– Intended as a temporary fix
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Wi-Fi Protected Access 2 (WPA2)
(continued)
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Transitional Security Model
• Should only be implemented as a temporary solution
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Authentication
• Shared key authentication
– Should be used instead of open system authentication
– Uses WEP keys for authentication
– Based on a challenge-response scheme
• SSID beaconing
– Should be turned off
– May prevent a “casual” unauthorized user or novice
attacker from capturing the SSID
• And entering the network
– Use a hard-to-guess SSID in a WLAN
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Authentication (continued)
• MAC address filtering limitations
– Managing a large number of MAC addresses is
difficult
– Does not provide an easy means to temporarily allow
a guest user to access the network
– WLANs initially exchange MAC addresses in cleartext
– A MAC address can be “spoofed” or substituted
• DHCP restrictions
– DHCP “leases” IP addresses to clients to use while
they are connected to the network
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Authentication (continued)
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Authentication (continued)
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WEP Encryption
• Should be turned on
– If no other options are available for encryption
• The longest WEP key available should be used for
added security
– Most vendors have the option of a 128-bit WEP key
• There is evidence that WEP passphrase generators
may create predictable keys
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WEP Encryption (continued)
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Personal Security Model
• Designed for single users or small office/home office
(SOHO) settings
– Generally 10 or fewer wireless devices
• Intended for settings in which an authentication
server is unavailable
• Divided into two parts, WPA and WPA2
– WPA2 should always be used instead of WPA
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WPA Personal Security
• PSK authentication
– Purchasing, installing, and managing an
authentication server is costly
• May require special technical skills
– PSK functions
• Used to authenticate the user
• Plays a role in encryption
– PSK vulnerabilities
• Key management
• Passphrases
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WPA Personal Security (continued)
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WPA Personal Security (continued)
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WPA Personal Security (continued)
• PSK authentication (continued)
– PSK key management weakness
• Distribution and sharing of PSK keys is performed
manually
• PSK only uses a single key
• Changing the PSK key requires reconfiguring the key on
every wireless device and all APs
• To allow a guest user to have access to a PSKWLAN,
the key must be given to that guest
– PSK passphrase
• 64-bit hexadecimal number
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WPA Personal Security (continued)
• PSK authentication (continued)
– PSK passphrases of fewer than 20 characters can be
subject to offline dictionary attacks
– Linksys’ SecureEasySetup (SES)
• Software and hardware interface
• Creates and distributes a strong PSK key
• TKIP encryption
– TKIP is designed to fit into existing WEP procedure
– Wireless device has two keys
• 128-bit encryption key called the temporal key and a 64bit MIC
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WPA Personal Security (continued)
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WPA Personal Security (continued)
• TKIP encryption (continued)
– TKIP components
• MIC
• IV sequence
• TKIP key mixing
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WPA2 Personal Security
• PSK authentication
– PSK keys are automatically changed (called rekeying)
• And authenticated between devices after a specified
period
– Known as the rekey interval
• AES-CCMP encryption
– AES is used in WPA2 for data encryption
– AES-CCMP is the encryption protocol in the 802.11i
standard
• CCMP is based upon the Counter Mode with CBC-MAC
(CCM)
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WPA2 Personal Security (continued)
• AES-CCMP encryption (continued)
– CCM provides data privacy
– CBC-MAC provides data integrity and authentication
– AES algorithm processes blocks of 128 bits
• Length of the cipher keys and number of rounds can
vary
– It is recommended that AES encryption and decryption
be performed in hardware
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WPA2 Personal Security (continued)
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Enterprise Security Model
• Most robust level of security
• Designed for medium to large-sized organizations
• Intended for settings in which an authentication
server is available
• Divided into two parts, WPA and WPA2
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WPA Enterprise Security
• IEEE 802.1x authentication
– Provides an authentication framework for all IEEE
802-based LANs
– Elements
• Supplicant
• Authenticator
• Authentication server
– IEEE 802.1x supplicant
• Software that implements the IEEE 802.1x framework
• May be included in the client operating system or WNIC
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WPA Enterprise Security (continued)
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WPA Enterprise Security (continued)
• IEEE 802.1x authentication (continued)
– Authentication server
• Stores the list of the names and credentials of
authorized users to verify their authenticity
• Typically a Remote Authentication Dial-In User Service
(RADIUS) server is used
– Allows a company to maintain user profiles in a
central database that all remote servers can share
• Other options
– Structured Query Language (SQL)
– Lightweight Directory Access Protocol (LDAP)
– Microsoft Active Directory
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WPA Enterprise Security (continued)
• TKIP encryption
– Should be considered an interim WPA enterprise
security solution
– A more robust encryption protocol is AES-CCMP
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WPA2 Enterprise Security
• IEEE 802.1x authentication
– Disadvantage
• High cost involved with purchasing, installing, and
maintaining an authentication server
• AES-CCMP encryption
– A 128-bit key length is used
– AES encryption includes four stages that make up one
round
• Each round is iterated 10 times
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WPA2 Enterprise Security (continued)
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WPA2 Enterprise Security (continued)
• Robust Secure Network (RSN)
– Uses dynamic negotiation of authentication and
encryption algorithms
• Between access points and wireless devices
– RSNs evolve as vulnerabilities are exposed or
improved security is introduced
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Summary
• Additional security solutions
– IEEE 802.11i
– Wi-Fi Protected Access (WPA)
– Wi-Fi Protected Access Version 2 (WPA2)
• IEEE 802.11i standard provided a more solid wireless
security model
– Uses AES and IEEE 802.1x port security
• WPA is a subset of 802.11i and addresses both
encryption and authentication
– Uses Temporal Key Integrity Protocol (TKIP) and a
Message Integrity Check (MIC)
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Summary (continued)
• The transitional security model should be
implemented only as a temporary solution
• The personal security model is designed for single
users or small office home office (SOHO)
• The enterprise security model is designed for medium
to large-sized organizations
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