Security+ Guide to Network Security Fundamentals, Third Edition Chapter 6 Wireless Network Security

Security+ Guide to Network Security Fundamentals, Third

Edition

Chapter 6Wireless Network Security

Security+ Guide to Network Security Fundamentals, Third Edition

Objectives

• Describe the basic IEEE 802.11 wireless security protections

• Define the vulnerabilities of open system authentication, WEP, and device authentication

• Describe the WPA and WPA2 personal security models

• Explain how enterprises can implement wireless security

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IEEE 802.11 Wireless Security Protections

• Institute of Electrical and Electronics Engineers (IEEE)– The most widely known and influential organization for

computer networking and wireless communications

• In the early 1980s, the IEEE began work on developing computer network architecture standards– This work was called Project 802

• In 1990, the IEEE formed a committee to develop a standard for WLANs– That operate at a speed of 1 and 2 million bits per

second (Mbps)3


IEEE 802.11 Wireless Security Protections (continued)

• In 1997, the IEEE approved the IEEE 802.11 WLAN standard

• Revisions– IEEE 802.11a– IEEE 802.11b– IEEE 802.11g– IEEE 802.11n

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Controlling Access

• Controlling wireless access of devices to the WLAN – Accomplished by limiting a device’s access to the

access point (AP)

• By restricting access to the AP, only those devices that are authorized are able to connect to the AP and become part of the wireless network

• The IEEE 802.11 standard does not specify how to implement controlling access

• Almost all wireless AP vendors implement access control through Media Access Control (MAC) address filtering

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Security+ Guide to Network Security Fundamentals, Third Edition 6

Controlling Access (continued)





• MAC address filtering is usually implemented by permitting instead of preventing

• Wired Equivalent Privacy (WEP)– Designed to ensure that only authorized parties can

view transmitted wireless information– Uses encryption to protect traffic

• The IEEE 802.11 committee designed WEP to meet the following criteria:– Efficient, exportable, optional, self-synchronizing, and

reasonably strong

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• IEEE 802.11 WEP shared secret keys must be a minimum of 64 bits in length

• The options for creating keys are as follows:– 64-bit key– 128-bit key– Passphrase

• The AP and devices can hold up to four shared secret keys– One of which must be designated as the default key

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• Device authentication– Wireless LANs cannot limit access to the wireless

signal by walls or doors• Sometimes called data emanation

• Types of authentication supported by the 802.11 standard– Open system authentication

• See Figure 6-6

– Shared key authentication• See Figure 6-7

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Vulnerabilities of IEEE 802.11 Security

• The primary vulnerabilities are in the areas of open system authentication, MAC address filtering, and WEP

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Open System Authentication Vulnerabilities

• Open system authentication is considered weak because authentication is based on only one factor:– A match of SSID

• The easiest way to discover the SSID is to actually do nothing– Exploits the beaconing process

• Once a wireless device receives a beacon frame, it can attempt to join the network– By sending an association request frame back to the

AP

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Open System Authentication Vulnerabilities (continued)

• Passive scanning– The most common type of scanning– A wireless device simply listens for a beacon frame

for a set period of time

• For a degree of protection, some wireless security sources encourage users to configure their APs to prevent the beacon frame from including the SSID – But instead require the user to enter the SSID

manually on the wireless device

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Open System Authentication Vulnerabilities (continued)

• Problems arise when the SSID is not beaconed– Can affect roaming– Can also affect devices running Microsoft Windows XP

• The SSID can be easily discovered even when it is not contained in beacon frames– Still is transmitted in other management frames sent

by the AP

• Configuring an access point to not allow the beacon frame to include the SSID provides virtually no protection

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MAC Address Filtering Weaknesses

• MAC addresses are initially exchanged in an unencrypted format through the WLAN– An attacker can easily see the MAC address of an

approved device and use it to join the network

• Managing a large number of MAC addresses can pose significant challenges

• MAC address filtering does not provide a means to temporarily allow a guest user to access the network – Other than manually entering the user’s MAC address

into the access point

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WEP

• To encrypt packets WEP can use only a 64-bit or 128-bit number– Which is made up of a 24-bit initialization vector (IV)

and a 40-bit or 104-bit default key– The relatively short length of the default key limits its

strength

• WEP implementation violates the cardinal rule of cryptography:– Anything that creates a detectable pattern must be

avoided at all costs– IVs would start repeating in fewer than seven hours

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WEP (continued)

• Because of the weaknesses of WEP– Possible for an attacker to identify two packets

derived from the same IV (called a collision)

• Keystream attack– A method of determining the keystream by analyzing

two packets that were created from the same IV

Security+ Guide to Network Security Fundamentals 23


WEP (continued)


WEP (continued)


Personal Wireless Security

• The wireless security requirements for personal wireless security are most often based on two models promoted by the Wi-Fi Alliance:– WPA Personal Security– WPA2 Personal Security

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WPA Personal Security

• Wireless Ethernet Compatibility Alliance (WECA)– A consortium of wireless equipment manufacturers and

software providers formed to promote wireless network technology

• WECA goals:– To encourage wireless manufacturers to use the IEEE

802.11 technologies– To promote and market these technologies– To test and certify that wireless products adhere to the

IEEE 802.11 standards to ensure product interoperability

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WPA Personal Security (continued)

• In 2002, the WECA organization changed its name to Wi-Fi (Wireless Fidelity) Alliance

• In October 2003 the Wi-Fi Alliance introduced Wi-Fi Protected Access (WPA)– WPA had the design goal to protect both present and

future wireless devices, addresses both wireless authentication and encryption

• PSK addresses authentication and TKIP addresses encryption

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• Preshared key (PSK) authentication– Uses a passphrase to generate the encryption key

• When using PSK, a key must be created and entered into both the access point and all wireless devices– Prior to the devices communicating with the AP

• The PSK is not used for encryption– Instead, it serves as the starting point (seed) for

mathematically generating the encryption keys

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• WPA replaces WEP with an encryption technology called Temporal Key Integrity Protocol (TKIP)

• TKIP has several advantages over WEP:– TKIP uses a longer 128-bit key– TKIP keys are known as per-packet keys– When coupled with other technologies, TKIP provides an

even greater level of security

• WPA also replaces the (CRC) function in WEP with the Message Integrity Check (MIC)– Designed to prevent an attacker from capturing, altering,

and resending data packets

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WPA2 Personal Security

• Wi-Fi Protected Access 2 (WPA2)– Introduced by the Wi-Fi Alliance in September 2004

– The second generation of WPA security

– Still uses PSK authentication but instead of TKIP encryption it uses enhanced data encryption

• PSK Authentication– Intended for personal and small office home office users

who do not have advanced server capabilities

– PSK keys are automatically changed and authenticated between devices after a specified period of time known as the rekey interval

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WPA2 Personal Security (continued)

• PSK key management weaknesses:– The distribution and sharing of PSK keys is performed

manually without any technology security protections– PSK only uses a single key– Changing the PSK key requires reconfiguring the key

on every wireless device and on all access points– In order to allow a guest user to have access to a

PSK WLAN, the key must be given to that guest

• A second area of PSK vulnerability is the use of passphrases

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• A PSK is a 64-bit hexadecimal number– The most common way in which this number is

generated is by entering a passphrase• Consisting of letters, digits, punctuation, etc. that is

between 8 and 63 characters in length

– PSK passphrases of fewer than 20 characters can be subject to a specific type of attack and broken

• AES-CCMP Encryption– Encryption under the WPA2 personal security model

is accomplished by AES-CCMP

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• CCMP is based upon the Counter Mode with CBC-MAC (CCM)– Of the Advanced Encryption Standard (AES)

encryption algorithm

• CCM is the algorithm providing data privacy– While the Cipher Block Chaining Message

Authentication Code (CBCMAC) component of CCMP provides data integrity and authentication

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Enterprise Wireless Security

• The enterprise wireless security options can be divided into those that follow the IEEE 802.11i standard and those that follow the WPA and WPA2 models

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IEEE 802.11i

• The IEEE 802.11i wireless security standard– Addresses the two main weaknesses of wireless

networks: encryption and authentication

• Encryption is accomplished by replacing WEP’s original PRNG RC4 algorithm– With a stronger cipher that performs three steps on

every block (128 bits) of plaintext

• IEEE 802.11i authentication and key management is accomplished by the IEEE 802.1x standard

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IEEE 802.11i (continued)

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IEEE 802.11i (continued)

• Key-caching– Stores information from a device on the network so if

a user roams away from a wireless access point and later returns, he does not need to re-enter all of the credentials

• Pre-authentication– Allows a device to become authenticated to an AP

before moving into range of the AP

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WPA Enterprise Security

• The WPA Enterprise Security model is designed for medium to large-size organizations– Provides improved authentication and encryption over

the personal model on a wireless LAN• The authentication used is IEEE 802.1x and the

encryption is TKIP

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WPA Enterprise Security (continued)

• IEEE 802.1x Authentication– Provides an authentication framework for all IEEE

802-based LANs– Uses port-based authentication mechanisms– Does not perform any encryption

• TKIP Encryption– An improvement on WEP encryption– Designed to fit into the existing WEP procedure

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WPA Enterprise Security (continued)

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WPA2 Enterprise Security

• Provides the highest level of secure authentication and encryption on a wireless LAN

• Authentication used is IEEE 802.1x and the encryption is AES-CCMP

• IEEE 802.1x authentication provides the most robust authentication for a WPA2 enterprise model WLAN

• Encryption is based on the stronger AES-CCMP– Only the 128-bit key and 128-bit block are mandatory

for WPA2

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WPA2 Enterprise Security (continued)

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Enterprise Wireless Security Devices

• Thin Access Point– An access point without the authentication and

encryption functions• These features reside on the wireless switch

• Advantages– The APs can be managed from one central location– All authentication is performed in the wireless switch

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Enterprise Wireless Security Devices (continued)

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• Wireless VLANs– Can be used to segment traffic and increase security– The flexibility of a wireless VLAN depends on which

device separates the packets and directs them to different networks

• See Figures 6-14 and 6-15

• For enhanced security many organizations set up two wireless VLANs– One for employee access– One for guest access

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• Rogue Access Point Discovery Tools– Wireless protocol analyzer

• Allows auditing the airwaves for rogue access points

– Monitoring the RF frequency requires a special sensor called a wireless probe

• Types of wireless probes:– Wireless device probe– Desktop probe– Access point probe– Dedicated probe

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Summary

• The initial IEEE 802.11 standard contained security controls for protecting wireless transmissions from attackers

• The Wi-Fi Alliance has introduced two levels of personal security– Wi-Fi Protected Access (WPA) and Wi-Fi Protected

Access 2 (WPA2)

• Enterprise wireless security requires different security models from personal wireless security

• Additional wireless security devices can be used to defend against attackers

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Documents

Security+ Guide to Network Security Fundamentals, Third Edition Chapter 6 Wireless Network Security