Wireless Network Security Position Paper - Technical

Transcription

1 Wireless Network Security Position Paper - Technical Management, Operational and Technical Issues and Recommendations for the Secure Deployment of Wireless Local Area Networks VERSION 1.1 December 2007

2 Acknowledgement This document was written with the assistance of the Department of the Premier and Cabinet.

3 Table of Contents 1. Purpose and Scope Position Statement Target Audience Introduction Overview of Wireless Technologies Wireless Networks Wireless Network Components and Architectural Models Wireless Technologies and Standards IrDA Bluetooth IEEE WLAN WLAN Security Security Objectives Inherent Characteristics Threats Countermeasures Management Countermeasures Operational Countermeasures Technical Countermeasures...18 WLAN Checklist...19 WPAN Checklist Recommendations...21 Recommendation 1 Develop a Strategy...21 Recommendation 2 Develop a Business Case...21 Recommendation 3 Develop Policies and Ensure Compliance...21 Recommendation 4 Monitor for Wireless Devices...21 Recommendation 5 Use only Best Practice WLAN Mode Conclusion Appendix A IEEE802.11i Security Technical Discussion Pre-IEEE i Security Service Set Identifier (SSID) Media Access Control (MAC) Address Filters Wired Equivalent Privacy (WEP) IEEE i Security Appendix B Acronyms and Abbreviations Appendix C Glossary of Terms Appendix D References...31

4 1. Purpose and Scope The purposes of this paper are to raise awareness of security risks posed by wireless computer networks, and to provide agencies with guidance for establishing secure wireless networks. This paper includes suggested management, operational and technical countermeasures to help mitigate security risks specific to wireless computing technologies. A previous paper, Securing Wireless Technologies a Discussion Paper 1, was developed in October 2002 and updated and re-released in September 2006 to raise awareness of the security issues associated with wireless networks. This more comprehensive paper, and a higher-level Wireless Network Security Position Paper Overview for CEOs, have been developed in response to the Auditor General's Second Public Sector Performance Report 2007, Report 3 April This paper provides some general information on wireless networks and wireless network security. It provides specific information for Wireless Local Area Networks (WLANs) using the standard Institute of Electrical and Electronics Engineers (IEEE) Other wireless technologies are outside the scope of this paper, however for completeness some general information is also provided on IrDA and Bluetooth. Recommendations for using external networks, such as public Internet access points ( hot spots ), are also outside the scope of this paper. 1 Department of Finance 4

5 2. Position Statement Key findings of the Auditor General's Second Public Sector Performance Report 2007, Report 3 April 2007 show serious weaknesses at the strategic, policy and operational levels in almost all agencies audited that had deployed wireless networks. Premier s Circular 2004/09 (Computer Information and Internet Security) noted that on 20 January 2003, Cabinet directed that the Chief Executive Officer of each agency is responsible for ensuring their agency implements an appropriate level of information and Internet security. Agencies should consider and implement the recommendations laid out in this paper for new or existing wireless networks. Department of Finance 5

6 3. Target Audience This paper covers details specific to wireless technologies and solutions. This paper is technical in nature; however it provides the necessary background (and other reference material) to understand the topics that are discussed. The following list highlights how different people might use this paper: Managers who are planning to employ wireless networked computing devices in their agencies Systems engineers and architects who design and implement wireless networks System and network administrators who administer, patch, secure or upgrade wireless networks Auditors, security consultants, and others who perform security assessments of wireless environments Researchers and analysts who are trying to understand the underlying wireless technologies This paper assumes that the readers have at least some operating system, networking, and security expertise. Because of the constantly changing nature of the wireless security industry and the threats and vulnerabilities to these technologies, readers are strongly encouraged to take advantage of other resources (including those listed in this paper) for more current and detailed information. Department of Finance 6

7 4. Introduction Traditional wired networks use cables to transfer information, and these are protected by physical controls, such as buildings, that enclose them. To gain unauthorised access to a wired network, you must bypass the physical security of the building or breach network perimeter security devices, such as firewalls. While wireless networks are exposed to many of the same risks as wired networks, they are also vulnerable to additional risks. Wireless networks transmit data through the air using radio frequencies. These wireless signals can travel through the walls, ceilings and windows of buildings up to hundreds of metres outside of the building walls, and are accessible by anyone in range thus providing a network access point that is beyond the physical security controls of the wired network. Once they have accessed systems, intruders can launch denial of service attacks, steal identities, violate the privacy of legitimate users, insert viruses or malicious code, and disable operations. Sensitive information that is transmitted between two wireless devices can be intercepted and disclosed if not protected by strong encryption. Despite the additional security risks to networks, the use of wireless devices and WLANs is growing rapidly. Many devices today such as laptops are now wireless enabled by default. Wireless communications give great flexibility in information delivery and in responding to changes in ICT infrastructure needs. Wireless connectivity also creates new security risks that agencies need to understand and factor into their business decisions. A particular danger with wireless technologies highlighted by the Auditor General is that they can be easily procured and installed without the knowledge of management. As well, laptops connected to the wired network with the wireless card enabled pose an ongoing risk to agencies networks. Department of Finance 7

8 5. Overview of Wireless Technologies 5.1 Wireless Networks Wireless networks allow devices to be moved about with varying degrees of freedom and still maintain communication with each other. They also offer greater flexibility than cabled networks and significantly reduce the time and resources needed to set up new networks and allow for ad hoc networks to be easily created, modified or torn down. There are many forms of wireless networks. One way of categorizing wireless networks is to consider the relative range and complexity of each type of network. For example: Wireless Personal Area Network (WPAN) a small-scale wireless network that requires little or no infrastructure and operates within a short range. A WPAN is typically used by a few devices in a single room instead of connecting the devices with cables. Examples include print services or enabling a wireless keyboard or mouse to communicate with a computer. Section 5.3 contains additional information on technologies used to deploy WPANs. Wireless Local Area Networks (WLANs) are groups of wireless networking nodes within a limited geographic area, such as an office building or campus, that are capable of radio communications. WLANs are usually implemented as extensions to existing wired local area networks to provide enhanced user mobility. Section 5.3 contains additional information on technologies used to deploy WLANs. Wireless Metropolitan Area Networks (WMANs) can provide connectivity to users located in multiple facilities generally within a few miles of each other. Many WMAN implementations provide wireless broadband access to customers in metropolitan areas. Details of WMAN technologies and security are outside the scope of this paper. Wireless Wide Area Networks (WWANs) connect individuals and devices over large geographic areas. WWANs are typically used for mobile voice and data communications, as well as satellite communications. Details of WWAN technologies and security are outside the scope of this paper. Department of Finance 8

9 5.2 Wireless Network Components and Architectural Models IEEE has two fundamental architectural components, as follows: Station (STA). A STA is a wireless endpoint device, also called a client device. STAs enable end users to gain access and utilize resources provided by wireless networks. Examples include laptop computers, personal digital assistants, mobile phones and other consumer electronic devices with IEEE capabilities. Access Point (AP). An AP logically connects STAs with a distribution system (DS), which is typically an organisation's wired network. APs can also logically connect wireless STA with each other without accessing a distribution system. Wireless APs provide users with a mobile capability by allowing users to freely move within an APs coverage area while maintaining connectivity between the user's client device and the AP. APs can also be linked together using wired infrastructure to allow users to "roam" between APs within a building or campus. The IEEE standard also defines the following two WLAN design structures or configurations, as follows: Ad Hoc Mode. The ad hoc mode does not use APs. Ad hoc mode is sometimes referred to as infrastructureless because only peer-to-peer STAs are involved in the communications. This mode of operation is possible when two or more STAs are able to communicate directly to one another. Examples are laptops, mobile phones, PDAs, printers and scanners being able to communicate with each other without an AP. One of the key advantages of ad hoc WLANs is that theoretically they can be formed any time and anywhere, allowing multiple users to create wireless connections cheaply, quickly, and easily with minimal hardware and user maintenance. However, an ad hoc WLAN cannot communicate with external networks. A further complication is that an ad hoc network can interfere with the operation of an AP-based infrastructure mode network that exists within the same wireless space. Infrastructure Mode. In infrastructure mode, an AP logically connects STAs to each other or to a distribution system (DS), which is typically an organisation's wired network. The DS is the means by which STAs can communicate with the organisation's wired LANs and external networks such as the Internet. Infrastructure mode is the most commonly used mode for WLANs. Department of Finance 9

10 5.3 Wireless Technologies and Standards Wireless computer networks are generally based on infrared, radio or microwave transmissions using various protocol suites. The most common of these are: Infrared Data Association (IrDA); Bluetooth; and IEEE standard for Wireless Local Area Networks (WLANs). The focus of this paper is IEEE , however for completeness some general information is also provided on IrDA and Bluetooth IrDA IrDa infrared links typically establish single point-to-point connections at close range up to at least 1 metre to form a wireless Personal Area Network (WPAN). Examples include IrDA connections between two laptop devices or between a PDA and a printer or a mobile phone, where these devices are IrDA capable. IrDA is principally a line-of-sight transmission technology. It has no link level security and anyone within the unobstructed maximum 30 beam can monitor the transmission, including outside glass doors and windows and reflections from surfaces in rooms and vehicles Bluetooth Bluetooth is a short-range (approximately 10 metres), low bandwidth wireless technology designed to establish a wireless Personal Area Network (WPAN). The Bluetooth specification led to the development of the IEEE standard. It allows up to eight devices to connect together into a piconet. Examples include synchronizing a PDA with a computer, providing print services, enabling a wireless keyboard or mouse to communicate with a computer, and allowing mobile telephones wireless headsets and handsfree use in cars. Pairing of Bluetooth devices requires a shared secret or Personal Identification Number (PIN) that is entered manually in each of the devices and not transmitted in the clear. Eavesdropping on an authenticated Bluetooth session is difficult without the PIN. However, if the PIN is known (and 50% of used PINs are '0000') the key can be recovered from the pairing exchanges IEEE WLAN IEEE is the dominant WLAN standard. It was developed by a voluntary industry standards committee, and provides specifications for high-speed networks that support most of today's applications. The IEEE standard specifies 'over-the-air' interface between a wireless client and a base station or access point, as well as among wireless clients. The IEEE standard can be compared to the IEEE standard for Department of Finance 10

11 Ethernet for wired LANs. The IEEE specifications address both the Physical (PHY) and Media Access Control (MAC) layers and are tailored to resolve compatibility issues between manufacturers of WLAN equipment. The reliable coverage range for IEEE WLANs varies significantly depending on several factors, including data rate requirements and capacity, sources of Radio Frequency interference, physical area characteristics, power, connectivity, and antenna usage. The typical range for connectivity is up to approximately 100 metres indoors, with significantly greater ranges achievable outdoors. Increased power output and special high-gain directional antennas can increase the range to several kilometres. The IEEE standard has evolved through a series of amendments, either ratified or proposed, that build on the original standard. IEEE b and anecdotally IEEE802.11g are currently the most widely deployed WLAN technologies. IEEE i, the most recently ratified amendment, was specifically designed to overcome security shortcomings of the standard. This paper does not go into the detail of each of the amendments to the IEEE standard, however the technical security issues of pre- IEEE802.11i implementations and the IEEE802.11i amendment are discussed in some detail in Appendix A. Department of Finance 11

12 6. WLAN Security This section provides a high-level overview of general wireless network security. The information in this section is intended to apply to many types of wireless networks. It first lists the security objectives for wireless networks, the inherent characteristics of wireless technology, and the most common threats against the security objectives. It next discusses countermeasures to mitigate these risks from management, operational and technical perspectives. 6.1 Security Objectives Wireless technologies typically need to support several security objectives, the most common being: Confidentiality ensure that communications cannot be read by unauthorised parties Integrity detect any intentional or unintentional changes to data that occur in transit Availability ensure that devices and individuals can access a network and its resources whenever needed Access Control restrict the rights of devices or individuals to access a network or resources within a network The security objectives for wireless and wired networks are the same, as are the major high-level categories of threats that they face. However, while these objectives are well understood and addressed in the relatively mature wired network environment this has not always been the case in the new and rapidly evolving wireless environment. In itself, deployment of insecure wireless technology poses a new security threat to a connected wired network environment by providing a network access point that bypasses existing security controls and mechanisms in place. As such, the wireless network needs to be secured against both the threats that a connected wired network faces and the threats that are specific to wireless. Department of Finance 12

13 6.2 Inherent Characteristics Wireless communication is inherently insecure because it relies on an open transmission medium making it susceptible to attacks. IEEE WLANs are a broadcast technology, with the signal passing to and from any station (friend or foe) capable of receiving or transmitting it. This is virtually inescapable in day-to-day use, without the assistance of special purpose buildings or environments to contain electromagnetic emissions. These characteristics jeopardize confidentiality by providing information, not only in the content of the signal, the data in the message body and the identity information in the message headers, but in the signal itself, its strength and location. The characteristics of the medium make WLANs highly susceptible to Denial of Service attacks on the availability of the services. Examples are flooding (an attacker sends large numbers of messages at a high rate to prevent the wireless network from processing legitimate traffic), jamming (a device emits electromagnetic energy on the wireless network's frequency to make it unusable), or the easy insertion of unauthenticated management frames to deauthenticate or disassociate a STA from its controlling AP. These latter attacks can be used in isolation or as the initial part of a more sophisticated attack to interrupt communications as a prelude to various masquerading attacks. The lack of inherent confidentiality and weak protection of availability, coupled with the intrinsic ability for easy injection of traffic into the medium by any STA, anywhere, with sufficient transmitting power and appropriate antennae, also threatens WLAN information integrity. Hostile STAs may masquerade as legitimate STAs to an AP or as the legitimate AP to an unsuspecting STA or even both at the same time as in a man-in-the-middle attack, completely controlling the communications between the legitimate STA and AP. Department of Finance 13

14 6.3 Threats Most threats against wireless networks involve an attacker with access to the radio link between wireless devices. Several of the threats listed below rely on an attacker's ability to intercept and inject network communications. This highlights the most significant difference between protecting wireless and wired networks: the relative ease of intercepting wireless network transmissions and inserting new or altered transmissions from what is presumed as the authentic source. For a wired network, an attacker would have to gain physical access to the network or remotely compromise systems on the network: for a wireless network, an attacker simply needs to be within range of the wireless transmissions, making eavesdropping a particularly prevalent threat. Another common threat against wireless networks is the deployment of rogue wireless devices. For example, an attacker could deploy a device, most likely a rogue AP that has been configured to appear as part of an organisation's wireless network infrastructure. This provides a back door into the wired network, bypassing perimeter security mechanisms, such as firewalls. Additionally, if clients inadvertently connect to the rogue device, the attacker can view and manipulate the clients' communications. Attacks on wireless networks, either passive or active, are essentially on confidentiality, integrity and network availability. Attacks Passive Active Eavesdropping Traffic Masquerade Replay Analysis Message Modification Denial of Service Department of Finance 14

15 Passive Attack - An attack in which an unauthorised party gains access to an asset and does not modify its content. Eavesdropping - The attacker monitors transmissions for message content. An example of this attack is a person listening into the transmissions on a LAN between two workstations or tuning into transmissions between a wireless handset and a base station. Traffic Analysis. - The attacker, in a more subtle way, gains intelligence by monitoring the transmissions for patterns of communication. A considerable amount of information is contained in the flow of messages between communicating parties. Active Attack - An attack whereby an unauthorised party makes modifications to a message, data stream, or file. It is possible for these attacks to be detected but they may not always be preventable. Active attacks may take the form of one of four types (or combination thereof) listed below. Masquerading - The attacker impersonates an authorised user and thereby gains certain unauthorised privileges. Replay - The attacker monitors transmissions (passive attack) and retransmits messages as the legitimate user. Message Modification - The attacker alters a legitimate message by deleting, adding to, changing, or reordering it. Denial of Service - The attacker prevents or prohibits the normal use or management of communication facilities. 6.4 Countermeasures Organisations can mitigate risks to WLANs by applying countermeasures to address specific threats and vulnerabilities. Countermeasures at the management, operational and technical levels can be effective in reducing the risks commonly associated with WLANs Management Countermeasures In light of the security issues, any deployment of wireless technology on an agency's computing network must be subject to usual risk management processes and underpinned by a sound business case as to why this technology should be used. The cornerstone of an effective WLAN security strategy involves documenting, deploying and enforcing WLAN security policies and practices. Department of Finance 15

16 A security policy, and compliance therewith, is the foundation on which other operational and technical countermeasures are rationalised and implemented. A WLAN security policy should include the following: Centralise the management of Access Points so that each Access Point must authenticate to the controller before it is allowed onto the network Identify who may use WLAN technology in an agency Identify whether Internet access is required Describe who can install and configure access points and other wireless equipment Provide limitations on the location and physical security for access points Describe the type (and classification)of information that may be sent over the wireless links Describe conditions under which wireless devices are allowed to be used and operated Define standard security settings for access points Describe limitations on how the wireless device may be used, such as location Prohibit laptops connecting into the wired network if their wireless card is enabled Describe the hardware and software configuration of all wireless devices Provide guidelines on reporting losses of wireless devices and security incidents Provide guidelines for the protection of wireless clients to minimize/reduce theft Provide guidelines on the use of encryption and key management Define the frequency and scope of security assessments to include rogue wireless equipment discovery, and Use channel hopping Access Points to detect and triangulate rogue Access Points. Department of Finance 16

17 Organisations should ensure that all critical personnel are properly trained on the use of wireless technology. Network administrators need to be fully aware of the security risks that WLANs and wireless devices pose. They must work to ensure security policy compliance and to know what steps to take in the event of an attack. Finally, the most important countermeasure is trained and aware users Operational Countermeasures Physical security is a fundamental step for ensuring that only authorised users have access to wireless equipment. Physical security combines such measures as access controls, personnel identification, and external boundary protection. As with facilities housing wired networks, facilities providing wireless network connectivity need physical access controls. For example, photo identification, card badge readers, or biometric devices can be used to minimise the risk of improper physical penetration of facilities. External boundary protection can include locking doors and installing surveillance cameras around the perimeter of a site to discourage unauthorised access to wireless networking components such as wireless APs. Additionally, security mechanisms should be put in place to prevent the theft, alteration or misuse of wireless infrastructure placed throughout an agency. Wired network infrastructure is generally placed within a wiring or network closet, but because APs are dispersed throughout a physical location, each device needs to be locked and secured in an appropriate fashion. It is important to consider the range of each AP that will be deployed as part of a WLAN environment. Design for security: when placing wireless APs for strategic coverage, consider signal bleed into uncontrolled areas where transmissions may be intercepted. If the range extends beyond the physical boundaries of the building's walls, the extension creates a security vulnerability. Agencies should use site survey tools to measure the range of AP devices, both inside and outside of the building where the wireless network is located. Every precaution should be taken to control WLAN signals, including the use of directional antennas to control Radio Frequency (RF) emanations. Directional antennas do not protect network links, they merely help control coverage range by limiting signal dispersion. Site survey tools should also be used determine the best channel to use. Over time other wireless networks may be implemented in the vicinity and if they use the same channel the performance of the wireless signal may be diminished due to co-channel interference. In addition, agencies should use wireless security assessment tools (e.g. vulnerability assessment) and regularly conduct scheduled audits. Department of Finance 17

18 6.4.3 Technical Countermeasures Technical countermeasures involve the use of hardware and software solutions to help secure the wireless environment. Software countermeasures include proper Access Point configurations (i.e. the operational and security settings on an AP), software patches and upgrades, authentication, intrusion detection systems, personal firewalls for wireless devices, and encryption. Hardware solutions include smart cards, virtual private networks (VPNs), public key infrastructure (PKI), a separate switching infrastructure for the wireless network (separating it from a wired network), and biometrics. It should be noted that hardware solutions, which generally have software components, are listed simply as hardware solutions. Additionally, due to the mobile nature of wireless networks, hard disk encryption is also highly recommended. Department of Finance 18

19 WLAN Checklist Here are some suggestions that might prevent hackers compromising your WLAN. This is a suggested checklist only, and mainly covers design, usage and configuration for WLAN devices. It does not cover other more technically detailed areas such as cryptographic protection or user authorisation features of IEEE Agencies should have their own checklist tailored to their business needs. Design for security: when placing wireless APs for strategic coverage, consider signal bleed into uncontrolled areas where transmissions may be intercepted. Survey your site for other wireless networks in the vicinity using the same channel that may cause co-channel interference. Segment the AP wired portion of your network on to a separate VLAN this allows you to separate this traffic and may lessen the access that a hacker gets to your LAN. Routing protocols should be filtered to the APs this can eliminate network injection attacks. Secure all user accounts with complex hard to guess passwords. Monitor your network traffic. Deny by default, and only allow specific IP ranges. Audit your authorised wireless networks, and proactively look for rogue wireless networks. Audit your wired networks for connected devices with wireless enabled. Use WPA2 in WPA2 Only Mode. Change the default SSID name to something that can't be easily guessed and that does not identify your network. Default SSIDs alert hackers to vulnerable WLANs. Disable the SSID broadcast option where the AP constantly broadcasts its SSID as a beacon in search of stations with which to connect. By turning this default feature off, stations must know the SSID in order to connect to the AP. Change any default passwords on wireless devices. Default passwords are set by the manufacturer and are known by hackers. By changing your passwords you can prevent hackers from going in and changing your network settings. Enable MAC address filtering. Disable laptop file and print sharing disabling this can further limit a hacker's ability to steal data or commandeer resources. Department of Finance 19

20 Protect wireless device personal firewalls can protect individual devices from attacks launched via the wireless connection or from the Internet. Control the reset function. A specific type of reset such as a power surge or power failure may restart the AP in the default factory settings that do not include encryption, authentication, or other security measures with which they were configured. Disable wireless by default on all client devices. Patch and upgrade regularly to ensure new vulnerabilities are corrected quickly. Ensure that your wireless users are fully trained in computer security awareness and the risks associated with wireless technology Make sure that APs are turned off when they are not used (e.g. after hours) Disable all non-essential protocols on the APs. Be aware that PDAs and laptops hidden in bags and briefcases can be recording all your WLAN traffic. WPAN Checklist Here are some suggestions that might prevent hackers compromising your WPAN. Beware of the infrared port. Disable it when not in use. Ensure the power up state has infrared disabled by default. When using infrared, disable any automatic acceptance of transfers. Infrared is a line-of-sight technology. Be aware of who and what is around you including unattended devices on desks and tables within the reflective area or outside glass doors and windows. Disable Bluetooth where possible Unplug Bluetooth expansion cards when not in use. Keep Bluetooth devices in the 'nondiscoverable' state, so that only the devices authorised to connect will attempt to. Only pair Bluetooth devices in a safe place clear of potential eavesdroppers (of either the pairing exchange or watching for the PIN). Use random Bluetooth PINs. Never use '0000'. On Bluetooth devices keep sensitive data in an encrypted form where possible. Department of Finance 20

21 7. Recommendations Implementing the recommendations presented in this paper for a new or existing WLAN will ensure that accepted wireless networking best practice is met, and will provide reasonable assurance that an agency is protected against most currently known WLAN security threats. To be effective, WLAN security should be incorporated throughout the life cycle of all WLAN solutions, involving everything from strategy and policy, through to procurement, operations and disposal. Recommendation 1 Develop a Strategy Agencies wishing to deploy wireless devices must be able to provide an overall documented vision for how the WLAN would support their business mission, creating a high-level strategy for the WLAN s implementation. Recommendation 2 Develop a Business Case In light of the security issues, any deployment of wireless technology on an agency's computing network must be subject to usual risk management processes and underpinned by a sound business case as to why this technology should be used. Recognising and documenting the benefits, costs and risks in a business case is something that can be done relatively easily and does not require voluminous documentation. A business case should specify business and functional requirements for a WLAN solution. A business case for a WLAN is strengthened if it can link to an overall WLAN strategy. Recommendation 3 Develop Policies and Ensure Compliance The cornerstone of an effective WLAN security strategy involves documenting, deploying and enforcing WLAN security policies and practices. A security policy, and compliance therewith, is the foundation on which other operational and technical countermeasures are rationalised and implemented. A WLAN security policy should cover the areas detailed in section of this paper. Recommendation 4 Monitor for Wireless Devices All agencies should develop, and exercise, the capability to monitor for rogue wireless networks. Even agencies that do not believe they have any wireless devices on their network should have the capability to detect any rogue wireless devices that may have been installed without the knowledge or authority of the persons responsible for such matters. Creating a wireless access point or intercepting wireless signals can be done simply and cheaply and must therefore be monitored. As well, laptops connected to the wired network with the wireless card enable pose an ongoing risk to Department of Finance 21

22 agencies networks and should be monitored for by wireless and wired network detection capabilities. Agencies with WLANs installed should also periodically review security arrangements such as the strength of transmission signals and co-channel interference from other wireless networks in the vicinity. Recommendation 5 Use only Best Practice WLAN Mode An IEEE802.11i RSN using AES-CCMP with IEEE 802.1X and EAP-TLS authentication should be the only mode used for any government WLANs. At the time of writing, this is consistent with the mode required for the transmission of classified information (below Top Secret) in Commonwealth Government agencies that are bound by the security specifications set out in the Defence Signals Directorate Australian Government Information Security Manual (ISM). Whilst State Government agencies are not bound by the ISM it is regarded as best practice to follow the security instructions from this manual. Department of Finance 22

23 8. Conclusion The deployment of insecure wireless networks poses new security threats to agencies existing connected wired network environments by providing network access points that bypass existing security controls and mechanisms in place. Pre-IEEE i WLANs that rely on WEP have several well-documented security problems that can be exploited to circumvent or adversely impact network access control and authentication, confidentiality, integrity and availability. To address these, agencies using or considering WLANs should deploy IEEE802.11i RSN WLANs. It is also recommended that agencies deploying such wireless networks use a secure Extensible Authentication Protocol for key management rather than pre-shared keys. Agencies should consider and implement the recommendations above. A Wireless Network Security Position Paper Overview for CEOs that is a high-level distillation of issues and information in this paper is available. Any queries on the issues discussed in this paper or general requests for further information can be directed to: Gail Holt, Principal Policy Officer, Department of Finance on Department of Finance 23

24 9. Appendix A IEEE802.11i Security Technical Discussion The past four years have seen some dramatic leaps in WLAN security. With the original insecurities of WLANs being well known and easily exploited both industry and standards have moved to respond to the issues. Broadly speaking, wireless security can be divided into two eras pre- IEEE802.11i amendment and IEEE802.11i. 9.1 Pre-IEEE i Security To counter security issues, the original IEEE specification defined two means to validate the identities of wireless devices attempting to gain access to a WLAN open system authentication (Service Set Identifiers and Media Access Control address filtering) and shared key authentication (Wired Equivalent Protocol); neither of these is secure Service Set Identifier (SSID) The SSID acts as a WLAN identifier; it allows STAs to distinguish one WLAN from another. All devices trying to connect to a WLAN must use the same SSID. A client device cannot communicate with an established wireless network unless it is configured with the correct SSID. Because the SSID is broadcast in plaintext by the AP by default, an attacking node can read the SSID from beacon frames and use it to join the network as a legitimate node. Even if the APs beacon frames are disabled, since the SSID is transmitted in cleartext in the message headers, any node listening to the traffic can sniff it Media Access Control (MAC) Address Filters A MAC address is a unique 48-bit value that is assigned to a particular wireless network interface by the network card's vendor. Many WLAN implementations allow administrators to specify a list of authorised MAC addresses; the AP will permit devices with those MAC addresses only to use the WLAN. This is known as MAC address filtering. However, since the MAC address is not encrypted, it is simple to intercept traffic and identify MAC addresses that are allowed past the MAC filter. Unfortunately, almost all WLAN adapters allow applications to set the MAC address, so it is relatively trivial to spoof a MAC address, meaning attackers can gain unauthorised access easily Wired Equivalent Privacy (WEP) According to the IEEE standard, WEP was supposed "to provide data confidentiality that is subjectively equivalent to the confidentiality of a wired local area network". WEP relies on the RC4 cipher and a static secret key that is manually shared between all of the nodes in a wireless LAN. WEP was plagued with security issues in relation to the actual Department of Finance 24

25 implementation of the encryption algorithm, the key lengths, poor key management, authentication and message integrity. WEP has now been proven to be easily breached and cannot be relied upon to secure WLANs. 9.2 IEEE i Security In 2001 the IEEE set up a dedicated task group to amend the IEEE standard to create a replacement security solution, i. With the seriously broken WEP in the marketplace, the industry group Wireless Fidelity Alliance (Wi-Fi Alliance) could not wait for IEE802.11i to be ratified. Based on a snapshot of the then current draft IEEE802.11i/D3, it released an interim specification called Wi-Fi Protected Access (WPA), which addressed the WEP vulnerabilities in the original IEEE implementations and provided an immediate solution for WLANs operating in infrastructure mode. WPA is not available in ad hoc mode. Products implementing the WPA specification started to appear in mid The most significant difference between WPA and the IEEE802.11i drafts is that WPA does not require support for Advanced Encryption Standard (AES) because many existing IEE hardware components cannot support the computationally intensive AES encryption without additional hardware components. The IEEE802.11i amendment, the sixth amendment to the baseline standard IEEE802.11, introduced a range of new security features designed to overcome the shortcomings of WEP. It includes many security enhancements that leverage mature and proven technologies. For example, IEEE802.11i references the Extensible Authentication Protocol (EAP) standard, which is a means for providing mutual authentication between STAs and the WLAN infrastructure, as well as performing automatic cryptographic key distribution. The IEEE802.11i specification introduces the concept of a Robust Security Network (RSN), which is defined as a wireless security network that allows the creation of Robust Security Network Associations (RSNA) only. A RSNA is a logical connection between communicating IEEE entities established through the IEEE802.11i key management scheme, called the 4-Way Handshake, which is a protocol that validates that both entities share a pairwise master key (PMK), synchronises the installation of temporal keys, and confirms the selection and configuration of data confidentiality and integrity protocols. The entities obtain the PMK in one of two ways either the PMK is already configured on each device, in which case it is called a pre-shared key (PSK), or it is distributed as part of a successful EAP authentication Department of Finance 25

26 instance, which is a component of IEEE802.1X port-based access control. The PMK serves as the basis for the IEEE802.11i data confidentiality and integrity protocols that provide enhanced security over WEP. Most large enterprise deployments of RSN technology will use IEEE802.1X and EAP rather than the Pre-Shared Keys because of the difficulty of managing PSKs on numerous devices. IEEE802.1X is a standard that defines port-based access control that leverages EAP to provide centralised, mutual authentication. IEEE.802.1X was originally developed for wired LANs to prevent unauthorised use in open environments such as university campuses, but it has been used by IEEE802.11i for WLANs as well. The IEEE802.1X framework provides the means to block user access until authentication is successful, thereby controlling access to WLAN resources. A brief note on the Extensible Authentication Protocol (EAP) this protocol provides the authentication framework for IEEE802.11i RSNs that use IEEE802.1X port-based access control. EAP includes different methods to perform authentication and cryptographic key generation. Only some EAP methods, such as certain Transport Layer Security (TLS)-based methods can satisfy the security requirements for WLANs. Examples of these are EAP-TLS, EAP-Tunneled TLS [EAP-TTLS], and Protected EAP [PEAP]). The IEEE802.11i amendment defines two additional protocols for RSNAs: Temporal Key Integrity Protocol (TKIP) and Counter Mode with Cipher Block Chaining Message Authentication Code Protocol (CCMP). TKIP (and for that matter WEP) uses RC4 which is not an Australian Defence Signals Directorate approved cryptographic algorithm. Only CCMP uses the strong AES cryptographic algorithm that is required to be used to secure US Federal Government agencies IEEE based WLANs. AES is also the only Australian Defence Signals Directorate approved cryptographic algorithm. In conjunction with the ratification of the IEEE802.11i amendment in June 2004 the Wi-Fi Alliance announced its Wi-Fi Protected Access 2 (WPA2) certification for the interoperability of vendor equipment implementing the mandatory requirements of IEEE802.11i. However, WPA2 allows for interoperability with WPA. WPA implements a Transition Security Network (TSN) and is compatible with WPA2, but incompatible with WEP. Devices cannot service a mixture of WEP and WPA. The only WPA2 mode that supports a RSN is the WPA2-Only Mode. Any other mode will only form a TSN, and this is an important distinction in terms of the security of the WLAN. Department of Finance 26

27 10. Appendix B Acronyms and Abbreviations AES AP CCMP DS EAP EAP-TLS EAP-TTLS IEEE IrDA LAN MAC PDA PEAP PIN PKI PMK PSK RC4 RF RSN RSNA SSID STA TKIP TLS TSN TTLS VLAN Advanced Encryption Standard Access Point Counter Mode with Cipher Block Chaining Message Authentication Code Protocol Distribution System Extensible Authentication Protocol Extensible Authentication Protocol Transport Layer Security Extensible Authentication Protocol Tunneled Transport Layer Security Institute of Electrical and Electronic Engineers Infrared Data Association Local Area Network Media Access Control Personal Digital Assistant Protected Extensible Authentication Protocol Personal Identification Number Public Key Infrastructure Pairwise Master Key Pre-Shared Key Rivest Cipher 4 encryption algorithm Radio Frequency Robust Security Network Robust Network Association Service Set Identifier Station Temporal Key Integrity Protocol Transport Layer Security Transition Security Network Tunneled Transport Layer Security Virtual Local Area Network Department of Finance 27

28 VPN WEP Wi-Fi WLAN WMAN WPA WPAN WWAN Virtual Private Network Wired Equivalent Privacy Wireless Fidelity Wireless Local Area Network Wireless Metropolitan Area Network Wi-Fi Protected Access Wireless Personal Area Network Wireless Wide Area Network Department of Finance 28

29 11. Appendix C Glossary of Terms Access Point (AP): A device that logically connects wireless client devices operating in infrastructure to one another and provides access to a distribution system, if connected, which is typically an organisation s enterprise wired network. Ad Hoc Network: A wireless network that dynamically connects wireless client devices to each other without the use of an infrastructure device, such as an access point or base station. Base Station: A two-way radio installed at a fixed location to provide wireless access for WMAN clients. Flooding: An attacker sending large numbers of messages at a high rate to prevent the network from processing legitimate traffic. Infrared (IR): An invisible band of radiation at the lower end of the electromagnetic spectrum. It starts at the middle of the microwave spectrum and extends to the beginning of visible light. Infrared transmission requires an unobstructed line of sight between transmitter and receiver. It is used for wireless transmission between computer devices, as well as for most handheld remotes for TVs, video, and stereo equipment. Infrastructure Network: A wireless network that requires the use of an infrastructure device, such as an access point or a base station, to facilitate communication between client devices. Jamming: A device emitting electromagnetic energy on a wireless network s frequency to make it unusable. Media Access Control (MAC): A unique 48-bit value that is assigned to a particular wireless network interface by the manufacturer. Piconet: A small Bluetooth network created on an ad hoc basis that includes two or more devices. Range: The maximum possible distance for communicating with a wireless network infrastructure or wireless client. Robust Security Network (RSN): A wireless security network that only allows the creation of Robust Security Network Associations (RSNA). Robust Security Network Association (RSNA): A logical connection between communicating IEEE entities established through the IEEE i key management scheme, also known as the four-way handshake. Department of Finance 29

30 Service Set Identifier (SSID): A name assigned to a WLAN that allows stations to distinguish one WLAN from another. Station (STA): A client device in a wireless network. Wi-Fi: A term that specifically refers to technology certified to be interoperable between vendors by the industry-based 'Wireless Fidelity Alliance'. Its use has been generalized in common use to refer to any of the IEEE series of protocols and their implementations. Wired Equivalent Privacy (WEP): A security protocol, specified in the IEEE standard, that is designed to provide a WLAN with a level of security and privacy comparable to what is usually expected of a wired LAN. However, WEP is no longer considered a viable encryption mechanism due to known weaknesses. A WEP network should be considered equivalent to an unprotected network. Wireless Bridge: A device that links two wired networks, generally operating at two different physical locations, through wireless communications. Wireless Local Area Network (WLAN): A group of wireless APs and associated infrastructure within a limited geographic area, such as an office building or campus, that are capable of radio communications. WLANs are usually implemented as extensions to existing wired local area networks to provide enhanced user mobility. Wireless Metropolitan Area Network (WMAN): A wireless network that provides connectivity to users located in multiple facilities generally within a few miles of each other. Many WMAN implementations provide wireless broadband access to customers in metropolitan areas. Wireless Personal Area Network (WPAN): A small-scale wireless network that requires little or no infrastructure and operates within a short range. A WPAN is typically used by a few devices in a single room instead of connecting the devices with cables. Wireless Technology: A technology that enables one or more devices to transmit and receive data by means of a signal that uses some part of the electromagnetic spectrum. Department of Finance 30

31 12. Appendix D - References 1. Defence Signals Directorate (Australian Department of Defence). Australian Government Information and Communications Technology Security Manual (ACSI 33). September Department of Education and Training (Government of Western Australia). ICT Specialist Standard Wireless LANs in Schools. 19 June Frankel, S et al. Establishing Wireless Robust Security Networks: A Guide to IEEE i. NIST Special Publication Office of the Auditor General (Government of Western Australia). Second Public Sector Performance Report 2007 Report 3. April Ossman, M. WEP: Dead again. SecurityFocus Infocus, 14 December Part 1. [Online] Available: 6. Ross, D. The Security of Wireless Computing Technolgies. AusCERT Conference Ross, D et al. Securely Deploying IEEE WLANs. AusCERT Conference Scarfone,K. and Dicoi, D. Wireless Network Security for IEEE802.11a/b/g and Bluetooth. NIST Special Publication Revision 1 (Draft) 9. Trusted Information Sharing Network for Critical Infrastructure Protection (Australian Government). Wireless Security Overview for CEOs. February Trusted Information Sharing Network for Critical Infrastructure Protection (Australian Government). Wireless Security Information for CIOs. February IEEE Standard , 1999 Edition. Also available at IEEE Standard i, 2004 Edition. Also available at IEEE Standard 802.1X, 2004 Edition. Also available at Various other papers and material available publicly on the Internet. Department of Finance 31

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