Wireless technology Principles of Security

Transcription

1 Wireless technology Principles of Security 1

2 Wireless technologies 2

3 Overview This module provides an introduction to the rapidly evolving technology of wireless LANs (WLANs). WLANs redefine the way the industry views LANs Wireless networking provides all the features and benefits of traditional LAN technologies without the limitations of wires or cables The freedom to roam while still maintaining connectivity has helped launch wireless networking to new heights 3

4 Wireless Technologies

5 Comparing a WLAN to a LAN

6 Benefits of wireless technology 6

7 Limitations of wireless technology 7

8 Introduction to wireless LANs A WLAN, just like a LAN, requires a physical medium through which transmission signals pass. Instead of using twisted-pair or fiber-optic cable, WLANs use infrared light (IR) or radio frequencies (RFs) The use of RF is far more popular for its longer range, higher bandwidth, and wider coverage. WLANs use the 2.4-gigahertz (GHz) and 5-GHz frequency bands Wireless networking provides the freedom and flexibility to operate within buildings and between buildings. 8

9 Wireless LAN Standards A number of standards have been developed to ensure that wireless devices can communicate They specify the RF spectrum used, data rates, how the information is transmitted The IEEE standard governs the WLAN environment a, b, g and n (802.11n is not ratified at the time of this writing). Collectively these technologies are referred to as Wi-Fi, Wireless Fidelity. 9

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12 Evolution of Wireless LANs Just as the Ethernet standard allows for data transmission over twisted-pair and coaxial cable, the WLAN standard allows for transmission over different media: Infrared light Three types of radio transmission within the unlicensed 2.4- GHz frequency bands: Frequency Hopping Spread Spectrum (FHSS) 1 Mbps Direct Sequence Spread Spectrum (DSSS) 11 Mbps Orthogonal Frequency-Division Multiplexing (OFDM) One type of radio transmission within the unlicensed 5-GHz frequency bands: 54 Mbps Orthogonal Frequency-Division Multiplexing (OFDM) 12

13 Wireless LAN standards 13

14 Wireless Standards

15 802.11a: Uses 5 GHz RF spectrum Not compatible with 2.4 GHz spectrum, i.e b/g/n devices Range is approximately 33% that of the b/g Relatively expensive to implement compared to other technologies Increasingly difficult to find a compliant equipment 15

16 802.11b: First of the 2.4 GHz technologies Maximum data-rate of 11 Mbps Range of approximately 46 m (150 ft) indoors/96 m (300 ft) outdoors 16

17 802.11g: 2.4 GHz technologies Maximum data-rate increase to 54 Mbps Same range as the b Backwards compatible with b 17

18 802.11n: Newest standard in development 2.4 GHz technologies (draft standard specifies support for 5 GHz-) Extends the range and data throughput. Backwards compatible with existing g and b equipment (draft standard specifies a support) 18

19 Wireless Technologies and devices 19

20 Wireless LAN components 20

21 Wireless LAN components An access point (AP) contains a radio transceiver. It can act as the center point of a stand-alone wireless network or as the connection point between wireless and wired networks. The roaming functionality provided by multiple APs allows wireless users to move freely throughout the facility, while maintaining seamless, uninterrupted access to the network. Any AP can be used as a repeater, or extension point, for the wireless network 21

22 Hidden Nodes A CSMA/CA feature called request to Request/Clear to send (RTS/CTS), access points allocate the medium to the requesting station for as long as is required to complete the transmission. When the transmission is complete, other stations can request the channel in a similar fashion.

23 Wireless LAN components Wireless router Wireless routers perform the role of access point, Ethernet switch, and router 23

24 WLANs and SSID When building a wireless network, it is important that the wireless components connect to the appropriate WLAN. This is done using a Service Set Identifier (SSID). The SSID is a case-sensitive, alpha-numeric string that is up to 32-characters. It is sent in the header of all frames transmitted over the WLAN Regardless of the type of WLAN installation, all wireless devices in a WLAN must be configured with the same SSID in order to communicate. 24

25 WLANs and SSID There are two basic forms of WLAN installations: Ad-hoc Infrastructure Mode 25

26 Ad-hoc The simplest form of a wireless network is created by connecting two or more wireless clients together in a peer-to-peer network. Does not include an AP All clients within an ad-hoc network are equal. The area covered by this network is known as an Independent Basic Service Set (IBSS). Used to exchange files and information between devices without the expense and complexity of purchasing and configuring an AP. 26

27 Infrastructure Mode Larger networks require a single device that controls communications in the wireless cell. AP will take over this role and control who can talk and when. Wireless communication most often used in the home and business environment. To communicate, each device must obtain permission from the AP. The AP controls all communications and ensures that all STAs have equal access to the medium. The area covered by a single AP is known as a Basic Service Set (BSS) or cell. 27

28 WLANs and SSID The area of coverage of a single AP is limited. To expand the coverage area, it is possible to connect multiple Basic Service Set (BSS) through a Distribution System (DS). This forms an Extended Service Set (ESS). An ESS uses multiple APs. Each AP is in a separate BSS. In order to allow movement between the cells without the loss of signal, BSSs must overlap by approximately 10% 28

29 Wireless channel Wireless technology uses an access method called Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA). CSMA/CA creates a reservation on the channel for use by a specific conversation. While a reservation is in place, no other device may transmit on the channel thus possible collisions are avoided. 29

30 Wireless channel The conversation between sender and receiver must be controlled. One way this is accomplished is through the use of Channels. Channels are created by dividing up the available RF spectrum Normally each wireless conversation makes use of a separate channel. 30

31 If there are three adjacent access points, use channels 1, 6, and 11. If there are just two, select any two that are five channels apart, such as channels 5 and b DSSS 31

32 Client and Access Point Association Beacons - Frames used by the WLAN network to advertise its presence. Probes - Frames used by WLAN clients to find their networks. Authentication - A process which is an artifact from the original standard, but still required by the standard. Association - The process for establishing the data link between an access point and a WLAN client.

33 Client and Access Point Association

34 Client and Access Point Association

35 Client and Access Point Association

36 Client and Access Point Association

37 Planning the Wireless LAN Network requirements specify that there must be a minimum of 6 Mb/s b

38 Planning the Wireless LAN Network requirements specify that there must be a minimum of 6 Mb/s b

39 Planning the Wireless LAN Network requirements specify that there must be a minimum of 6 Mb/s b

40 Security considerations on WLANs The ease of connectivity and the fact that the information is transmitted through the air also makes your network vulnerable to interception and attacks. Once an attacker have access to your network, they can use your Internet services for free, as well as access computers on the network to damage files, or steal personal and private information. These vulnerabilities in wireless networking require special security features and implementation methods to help protect your WLAN from attacks. 40

41 Treats to wireless security Unauthorized Access War drivers Hackers (Crackers) Employees Rogue Access Points A rogue access point is an access point placed on a WLAN that is used to interfere with normal network operation Man-in-the-Middle Attacks Denial of Service 41

42 Security considerations on WLANs The SSID broadcast feature can be turned off. Change the default setting such as SSIDs, passwords, and IP addresses in place. Even with SSID broadcast turned off and default values changed, attackers can learn the name of a wireless network through the use of these devices that intercept wireless signals 42

43 Limiting access to a WLAN MAC Address Filtering Requires the MAC addresses of all devices 43

44 Wired Equivalent Privacy (WEP) The IEEE standard includes WEP to protect authorized users of a WLAN WEP standard specified a 40-bit key Most vendors have extended WEP to 128 bits or more. Both the wireless client and the access point must have a matching WEP key. WEP is based upon an existing and familiar encryption type, Rivest Cipher 4 (RC4). 44

45 WPA- Wi-Fi Protected Access WPA also uses encryption keys from 64 bits up to 256 bits. WPA, unlike WEP, generates new, dynamic keys each time a client establishes a connection with the AP. WPA is considered more secure than WEP because it is significantly more difficult to crack. WPA allows user authentication through the IEEE 802.1x protocol x provides mutual authentication. Network and the user prove their identity to each other. An access point that supports 802.1x and its protocol, Extensible Authentication Protocol (EAP), acts as the interface between a wireless client and an authentication server such as a Remote Access Dial-In User Service (RADIUS) server. 45

46 Authentication on WLAN Authentication is the process of permitting entry to a network based on a set of credentials. The use of a username and password is a most common form of authentication. Two types of authentication were introduced with the original standard: Open authentication Pre Shared WEP Key authentication 46

47 Open Authentication By default, wireless devices do not require authentication. Clients are able to associate regardless of who they are. Open authentication should only be used on public wireless networks such as those found in many schools and restaurants. 47

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49 Pre-shared keys (PSK) With PSK both the AP and client must be configured with the same key or secret word. AP sends a random string of bytes to the client. The client accepts the string, encrypts it (or scrambles it) based on the key, and sends it back to the AP. PSK performs one-way authentication, that is, the host authenticates to the AP. PSK does not authenticate the AP to the host, nor does it authenticate the actual user of the host. 49

50 Pre-shared WEP keys (PSK) 50

51 Today, the standard that should be followed in most enterprise networks is the i standard. This is similar to the Wi-Fi Alliance WPA2 standard. For enterprises, WPA2 includes a connection to a Remote Authentication Dial In User Service (RADIUS) database. 51

52 Extensible Authentication Protocol (EAP) EAP provides mutual, or two-way, authentication as well as user authentication. When EAP software is installed on the client, the client communicates with a backend authentication server such as Remote Authentication Dial-in User Service (RADIUS). 52

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54 The access point blocks all data frames, except for 802.1x-based traffic. The 802.1x frames carry the EAP authentication packets via the access point to a server that maintains authentication credentials. This server is an Authentication, Authorization, and Accounting (AAA) server running a RADIUS protocol. If the EAP authentication is successful, the AAA server sends an EAP success message to the access point. 54

55 Encrytpion Two enterprise-level encryption mechanisms specified by i are certified as WPA and WPA2 by the Wi-Fi Alliance: Temporal Key Integrity Protocol (TKIP) TKIP is the encryption method certified as WPA. Advanced Encryption Standard (AES) 55

56 AES AES offers stronger encryption Cryptographic algorithm for use by United States government organizations to protect sensitive, unclassified information AES requires a coprocessor or additional hardware to operate. This means that companies need to replace existing access points and client NICs to implement AES AES specifies three key sizes, which are 128, 192, and 256 bits 56

57 Configuring Basic Wireless Settings

58 Configuring Security When you see "Personal" in a security mode, no AAA (Authentication, Authorization, Accounting)ser ver is used. "Enterprise" in the security mode name means a AAA server and EAP authentication is used.