cwna guide to wireless lan's second edition - chapter 9

CWNA Guide to Wireless LANs, Second Edition

Chapter NineImplementing Wireless LAN Security

CWNA Guide to Wireless LANs, Second Edition 2

Objectives

• 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


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


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


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


Dynamic WEP (continued)

Figure 9-1: Dynamic WEP


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


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


IEEE 802.11i (continued)

Table 9-1: Time needed to break AES



• 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



Figure 9-2: IEEE 802.1x


Wi-Fi Protected Access (WPA)

• Subset of 802.11i that addresses encryption and authentication

• Temporal Key Integrity Protocol (TKIP): Replaces WEP’s encryption key with 128-bit per-packet key– Dynamically generates new key for each packet

• Prevents collisions– Authentication server can use 802.1x to produce

unique master key for user sessions– Creates automated key hierarchy and management

system


Wi-Fi Protected Access (continued)

• Message Integrity Check (MIC): Designed to prevent attackers from capturing, altering, and resending data packets– Replaces CRC from WEP– CRC does not adequately protect data integrity

• Authentication accomplished via IEEE 802.1x or pre-shared key (PSK) technology– PSK passphase serves as seed for generating keys


Wi-Fi Protected Access (continued)

Figure 9-3: Message Integrity Check (MIC)


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


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


Summary of Wireless Security Solutions (continued)

Table 9-3: Wireless security solutions

Table 9-2: Wi-Fi modes


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


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


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


Authentication: MAC Address Filtering

Figure 9-6: MAC address filter


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


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


WPA Personal Security: PSK Authentication

• Uses passphrase (PSK) that is manually entered to generate the encryption key– PSK used a 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


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


WPA Personal Security: TKIP Encryption (continued)

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 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


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


WPA2 Personal Security: AES-CCMP Encryption (continued)

• AES encryption/decryption computationally intensive– Better to perform in hardware

Table 9-5: Personal security model


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


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


WPA Enterprise Security: IEEE 802.1x Authentication (continued)

Figure 9-8: 802.1x protocol



• 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



• 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


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


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 WAP

or WAP2 environment


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


WPA2 Enterprise Security: AES-CCMP Encryption (continued)

Table 9-6: Enterprise security model


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


Other Enterprise Security Tools: Virtual Private Network (continued)

• Endpoint: End of tunnel between VPN devices– Can local software, dedicated hardware device, or

even a firewall

• VPNs can be used in WLAN setting– Tunnel though WLAN for added security

• Enterprise trusted gateway: Extension of VPN– Pairs of devices create “trusted” VPN connection

between themselves– Can protect unencrypted packets better than a VPN

endpoint


Other Enterprise Security Tools: Wireless Gateway

• AP equipped with additional functionality– Most APs are wireless gateways

• Combine functionality of AP, router, network address translator, firewall, and switch

• On enterprise level, wireless gateway may combine functionality of a VPN and an authentication server– Can provide increased security for connected APs


Other Enterprise Security Tools: Wireless Intrusion Detection System

(WIDS)• Intrusion-detection system (IDS): Monitors

activity on network and what the packets are doing– May perform specific function when attack detected– May only report information, and not take action

• Wireless IDS (WIDS): Constantly monitors RF frequency for attacks– Based on database of attack signatures or on

abnormal behavior– Wireless sensors lie at heart of WIDS– Hardware-based have limited coverage, software-

based have extended coverage


Other Enterprise Security Tools: Captive Portal

• Web page that wireless users are forced to visit before they are granted access to Internet

• Used in one of the following ways:– Notify users of wireless policies and rules– Advertise to users specific services or products– Authenticate users against a RADIUS server

• Often used in public hotspots


Summary

• IEEE 802.11i and Wi-Fi Protected Access (WPA), have become the foundations of today’s wireless security

• Dynamic WEP attempts to solve the weak initialization vector (IV) problem by rotating the keys frequently, making it much more difficult to crack the encrypted packet

• The IEEE 802.11i standard provided a more solid wireless security model, such as the block cipher Advanced Encryption Standard (AES) and IEEE 802.1x port security


Summary (continued)

• WPA is a subset of 802.11i and addresses both encryption and authentication

• The transitional security model uses shared key authentication, turning off SSID beaconing, and implementing MAC address filtering

• The personal security model is designed for single users or small office home office (SOHO) settings of generally 10 or fewer wireless devices and does not include an authentication server


Summary (continued)

• The enterprise security model is intended for settings in which an authentication server is available; if an authentication server is not available the highest level of the personal security model should be used instead

• Additional security tools that can supplement the enterprise security model to provide even a higher degree of security include virtual private networks, wireless gateways, wireless intrusion detection systems (WIDS), and captive portals

cwna guide to wireless lan's second edition - chapter 9

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