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ITL Bulletin for April 2007




ITL Bulletin for April 2007
ITL Bulletin for April 2007



Forwarded from: Elizabeth Lennon 

ITL BULLETIN FOR APRIL 2007

SECURING WIRELESS NETWORKS

Shirley Radack, Editor
Computer Security Division
Information Technology Laboratory
National Institute of Standards and Technology
Technology Administration
U.S. Department of Commerce

Many users and organizations have found that wireless communications and 
devices are convenient, flexible, and easy to use. Wireless local area 
networks (WLANs) enable users with mobile devices that operate over 
radio frequencies to move from one place to another without being 
physically connected to a network. Portable computers, personal digital 
assistants (PDAs), and cell phones support the sharing of data and 
applications with network systems and other users with compatible 
devices, and provide access to network services such as wireless email, 
web browsing, and the Internet. Wireless communications can benefit 
organizations by reducing their wiring costs.

The mobile devices function within the range of the wireless network, 
usually limited to an area such as an office building or building 
complex. Since they transmit data through radio frequencies, wireless 
networks are open to intruders and especially vulnerable to security 
risks unless properly protected. Intruders have exploited the openness 
of wireless networks to access systems, destroy and steal data, and 
launch attacks that take over network bandwidth and deny service to 
authorized users.

Wireless Local Area Networks Standards and Security

The Information Technology Laboratory (ITL) of the National Institute of 
Standards and Technology (NIST) issued Special Publication (SP) 800-48, 
Wireless Network Security:  802.11, Bluetooth and Handheld Devices, in 
2002. This guide assists organizations in implementing a family of 
voluntary industry standards developed by the Institute of Electrical 
and Electronics Engineers (IEEE) to define the characteristics, the 
transmission of data, and the security of wireless local area networks. 
In addition to the IEEE 802.11b and 802.11g standards, NIST SP 800-48 
also discusses Bluetooth technology and wireless handheld devices such 
as text messaging devices, PDAs, and smart phones.

The IEEE 802.11 standards were based on a security method known as Wired 
Equivalent Privacy (WEP). Since this method had been subject to several 
well-documented security problems, the concerns about security led the 
standards developers to improve the security methodology with an 
amendment to the specifications (IEEE 802.11i).

The amendment introduces new security features to overcome the 
shortcomings of WEP and presents the concept of the Robust Security 
Network (RSN), a wireless security network with three main components:

* stations (STA) - wireless endpoint devices such as laptops, and 
  wireless handheld devices such as PDAs, text messaging devices, and 
  smart phones;

* access points (AP) - network devices that allow STAs to communicate 
  over radio frequencies and to connect to another network, such as the 
  organization's wired infrastructure; and

* authentication servers (AS) - WLAN components that provide 
  authentication services to STAs.

Threats to WLANs often involve an attacker with access to the radio link 
between two STAs or between a STA and an AP. The RSN framework, as 
described in IEEE 802.11i, provides for the creation of Robust Security 
Network Associations (RSNAs). RSNAs are wireless connections that 
provide moderate to high levels of assurance against WLAN security 
threats through the use of a variety of cryptographic techniques.

NIST SP 800-97, Establishing Wireless Robust Security Networks: 
A Guide to IEEE 802.11i

ITL recently issued NIST SP 800-97, Establishing Wireless Robust 
Security Networks: A Guide to IEEE 802.11i, to supplement NIST SP 800-48 
and to assist organizations in establishing and maintaining robust 
security for WLANs using the new security features that were developed 
for IEEE 802.11i. Written by Sheila Frankel and Karen Scarfone of NIST 
and by Bernard Eydt and Les Owens of Booz Allen Hamilton, the guide 
includes an overview of wireless networking, focusing on the IEEE 802.11 
family of WLAN standards. The publication explains the basic WLAN 
components and architectural models and provides an overview of WLAN 
security, including a review of the security features and weaknesses of 
the IEEE 802.11 specifications, and the features of the IEEE 802.11i 
amendment that improve WLAN security.

NIST SP 800-97 introduces the major security-related components that are 
defined in IEEE 802.11i and explains the security features and 
capabilities associated with the framework for RSNs. It provides 
extensive guidance on the planning and deployment of RSNs, the steps 
needed to establish RSNAs, data confidentiality and integrity protocols, 
and the cryptographic keys that are created and used by these protocols.

Other issues discussed include the five phases of operation that occur 
during RSN communications, starting with the discovery of a WLAN and 
ending in the termination of the connection; the types of frames used to 
carry information between RSN components; the flow of frames between 
components during each phase of RSN operation; and planning for the 
implementation of the Extensible Authentication Protocol (EAP). The EAP, 
which was designed to accommodate the use of new authentication methods 
as they are developed, should be used by organizations for most RSN 
deployments. Also discussed are the most common EAP methods, how 
organizations can select EAP methods appropriate to their environments, 
EAP security considerations, and the EAP architectural model and related 
support requirements.

A section of the guide focuses on validation testing of cryptographic 
products as required under Federal Information Processing Standard 
(FIPS) 140-2, Security Requirements for Cryptographic Modules, and the 
certification requirements as applied to IEEE 802.11 wireless networks. 
This section also provides an overview of the security specifications 
developed by the Wi-Fi Alliance, a nonprofit industry consortium of WLAN 
equipment and software vendors, which conducts a certification program 
for WLAN products. The certifications help organizations select 
interoperable WLAN products that can support RSNs. Recommendations for 
best practices related to WLAN security are summarized, and planned 
extensions to IEEE 802.11 are discussed.

Extensive appendices to NIST SP 800-97 include an acronym list, 
references and other sources of information, as well as a listing of 
online resources that provide additional information about IEEE 802.11i 
specifications and IEEE 802.11i security.

NIST SP 800-97 is available from NIST's website at 
http://csrc.nist.gov/publications/nistpubs/800-97/SP800-97.pdf. 

Recommendations for Wireless Network Security

NIST recommends that organizations adopt the following practices to 
improve the security of their wireless networks:

* Ensure that all WLAN components use Federal Information Processing 
  Standards (FIPS)-approved cryptographic algorithms to protect the 
  confidentiality and integrity of WLAN communications.

The IEEE 802.11i amendment defines two data confidentiality and 
integrity protocols for RSNAs: Temporal Key Integrity Protocol (TKIP) 
and Counter Mode with Cipher Block Chaining Message Authentication Code 
Protocol (CCMP). The guide discusses both protocols, as well as the 
cryptographic keys created and used by these protocols.

Federal agencies are required to use FIPS approved cryptographic 
algorithms that are contained in FIPS-validated cryptographic modules. 
Only the CCMP uses a FIPS-approved core cryptographic algorithm, the 
Advanced Encryption Standard (AES), as specified in FIPS 197. Since CCMP 
provides stronger assurance than WEP and TKIP, federal agencies are 
advised to use CCMP for securing IEEE 802.11-based WLANs.  Auxiliary 
security protection is required for legacy IEEE 802.11 equipment that 
does not support the use of the CCMP. Federal agencies should consult 
NIST SP 800-48 for specific recommendations for securing legacy IEEE 
802.11 implementations.


* Select IEEE 802.11 RSN authentication methods that meet the needs of 
  the organization's computing environments.

The RSN specified in IEEE 802.11 uses the EAP for the authentication 
phase of establishing an RSNA. EAP supports a wide variety of 
authentication methods, also called EAP methods. These methods include 
authentication based on passwords, certificates, smart cards, and 
tokens. EAP methods also can include combinations of authentication 
techniques, such as using a certificate followed by a password, or the 
option of using either a smart card or a token for authentication. These 
options enable organizations to integrate the EAP methods with other 
environments to which a WLAN might connect. Organizations have 
considerable discretion in choosing which EAP methods to employ; 
however, the choice of EAP method should be carefully considered since 
it can impact the protection provided by an RSN.

Because of the extensible nature of EAP, many EAP methods exist, and 
others are being developed. Some EAP methods may not satisfy the 
necessary security requirements for WLANs; for example, EAP methods that 
do not generate cryptographic keying material cannot be used for WLANs. 
In general, the current EAP methods that can satisfy WLAN security 
requirements are based on the Transport Layer Security (TLS) protocol. A 
primary distinction between TLS-based EAP methods is the level of public 
key infrastructure (PKI) support required; the EAP-TLS method requires 
an enterprise PKI implementation and certificates deployed to each STA, 
while most other TLS methods require certificates on each AS only. 
Organizations should use the EAP-TLS method whenever possible.

Because some EAP methods have not yet been adopted as voluntary industry 
standards and new methods are being developed, organizations are 
encouraged to obtain up-to-date information on EAP methods and standards 
when planning an RSN implementation, based on IEEE 802.11. See Appendix 
C of the guide for contact information.  Additionally, organizations 
should ensure that the cryptographic modules implementing the TLS 
algorithm for each product under consideration have been FIPS-validated.

Before selecting WLAN equipment, organizations should review their 
existing identity management infrastructure, authentication 
requirements, and security policy to determine the EAP method or methods 
that are most appropriate in their environments. They should then 
acquire systems that support the chosen EAP methods, and implement and 
maintain them carefully. See the guide for detailed guidance on planning 
EAP implementations, the available EAP methods, how organizations can 
select EAP methods, and additional EAP security considerations.


* Integrate existing authentication technology with the IEEE 802.11 RSN 
  WLAN to the extent feasible.

Although the RSN framework supports the use of pre-shared keys (PSK), 
organizations should choose to implement the IEEE 802.1X standard and 
EAP for authentication instead of using PSKs because of the resources 
needed for proper PSK administration and the security risks involved. 
IEEE 802.1X and EAP authentication requires an organization to use an 
AS, which may necessitate the use of a PKI. An organization that already 
has implemented ASs for web, email, file and print services, and other 
authentication needs, should consider integrating this technology into 
its RSN solution.  Most leading network operating systems and directory 
solutions offer the support needed for RSN integration.


* Ensure that the confidentiality and integrity of communications 
  between access points and authentication servers are sufficiently 
  protected.

The data confidentiality and integrity protocol, such as CCMP, used by 
an IEEE 802.11 RSN protects communications between STAs and APs. 
However, IEEE 802.11 and its related standards do not cover protection 
of the communications between the AP and AS.  Therefore, organizations 
deploying RSNs should ensure that communications between each AP and its 
corresponding ASs are protected sufficiently through the use of 
cryptography. Also, because of the importance of the ASs, organizations 
should pay particular attention to establishing and maintaining their 
security through operating system configuration, firewall rules, and 
other security controls.


* Use technologies that have the appropriate security certification from 
  NIST and interoperability certification from the Wi-Fi Alliance when 
  IEEE 802.11 RSNs are established.

To implement IEEE 802.11 RSNs, organizations may need to update or 
replace existing IEEE 802.11 equipment and software that cannot support 
RSNAs. They may also need to purchase additional equipment. The Wi Fi 
Alliance's Wi-Fi Protected Access 2 (WPA2) certification program 
facilitates the interoperability of WLAN products that implement IEEE 
802.11i systems with similar equipment from other vendors. Federal 
agencies should procure WPA2 products that use FIPS-approved encryption 
algorithms and that have been FIPS-validated. Organizations that plan to 
use authentication servers as part of their IEEE 802.11 RSN 
implementations should procure products with the WPA2 Enterprise level 
certification. Also, because the WPA2 certification is expanded 
periodically to test for interoperability with additional EAP methods, 
organizations should obtain the latest WPA2 information before making 
procurement decisions.


* Ensure that WLAN security considerations are incorporated into each 
  phase of the WLAN life cycle in the establishment and maintenance of 
  IEEE 802.11 RSNs.

Each of the phases of the life cycle in planning and implementing IEEE 
802.11 RSNs has special considerations for WLAN security. The five-phase 
life cycle model for WLANs, which is briefly summarized below, is based 
on the model discussed in NIST SP 800-64, Security Considerations in the 
Information System Development Life Cycle.

* Initiation Phase includes the tasks that an organization should 
  perform before it starts to design its WLAN solution: developing a 
  WLAN use policy; performing a WLAN risk assessment; and specifying 
  business and functional requirements for the solution, such as 
  mandating RSNAs for all WLAN connections.

* Acquisition/Development Phase includes Planning and Design, and 
  Procurement:

*  Planning and Design allows WLAN network architects to specify the 
  technical characteristics of the WLAN solution, such as authentication 
  methods, and the related network components, such as the firewall 
  rules. The WLAN network architects should also conduct a site survey 
  to help determine the architecture of the solution and how the WLAN 
  should be integrated with the existing authentication infrastructure, 
  including the organization's PKI.

* Procurement involves specifying the number and type of WLAN components 
  that must be purchased, the feature sets they must support such as 
  FIPS-validated encryption modules, and any certifications they must 
  hold such as WPA2 Enterprise.

* Implementation entails the configuration of procured equipment to meet 
  operational and security requirements, and the installation and 
  activation of the equipment on a production network, with the 
  appropriate event logging procedures enabled.

* Operations/Maintenance includes carrying out security-related tasks 
  that an organization should perform on an ongoing basis once the WLAN 
  is operational, including patching, periodic security assessment, log 
  reviews, and incident handling.

* Disposition encompasses the tasks that occur after a system or its 
  components have been retired, including preserving information to meet 
  legal requirements, sanitizing media that might contain sensitive 
  material, and disposing of equipment properly.

Best Practice Recommendations

NIST SP 800-97 summarizes over 50 best practice recommendations for WLAN 
security, grouped by the life cycle phase for which each recommendation 
is most relevant. NIST encourages organizations to adopt these best 
practice recommendations. RSNs are complex, involving multiple devices, 
protocols, and standards. The recommendations are presented in a way to 
enable organizations to manage their WLANs and to take actions that will 
provide reasonable assurance that the WLANs are protected from most 
security threats. The recommendations should be particularly helpful to 
organizations that have made a decision to integrate WLAN technology 
into their computer networks and want to determine the best way to do 
it. The recommendations will help those organizations that are already 
managing WLANs, but are not satisfied with the level of security they 
provide. When they upgrade, replace, and configure their infrastructure, 
they should enhance security by supporting RSNs and other security 
controls.

More Information

NIST publications assist organizations in planning and implementing a 
comprehensive approach to information security. For information about 
NIST standards and guidelines that are referenced in the security guide 
for wireless networks, as well as other security-related publications, 
see NIST's web page http://csrc.nist.gov/publications/index.html. 

Federal organizations should follow the guidance on general security 
controls that are discussed in NIST SP 800-53, Recommended Security 
Controls for Federal Information Systems, for minimum management, 
operational, and technical security controls for information systems. 
This publication is available on the web page listed above.

For information about FIPS 140-2, lists of FIPS-approved cryptographic 
products, and NIST's Cryptographic Module Validation Program, 
see http://csrc.nist.gov/cryptval/140-2.htm. 

Disclaimer
Any mention of commercial products or reference to commercial 
organizations is for information only; it does not imply recommendation 
or endorsement by NIST nor does it imply that the products mentioned are 
necessarily the best available for the purpose.



Elizabeth B. Lennon
Writer/Editor
Information Technology Laboratory
National Institute of Standards and Technology
100 Bureau Drive, Stop 8900
Gaithersburg, MD 20899-8900
Telephone (301) 975-2832
Fax (301) 975-2378


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