Wireless Security Background

Wireless Security Background

Wireless Networks The need for mobile computing Laptops, PDAs, Bluetooth devices Smart phones Enabling technology Wireless communication Two important characteristics Wireless links unreliable, vulnerable Mobility introduces new networking challenges 2

Wireless Networks Three elements End-point devices Laptop, PDA, smartphones, RFID tags Maybe stationary or mobile Usually power constrained Wireless infrastructure Base stations, e.g., wireless routers, access point Usually connected to wired network, e.g., Internet Relay packets between wireless devices and wired networks Wireless links Communication channel data rate varies transmission distance varies 3

Selected Wireless Standards 200 802.11n Data rate (Mbps) 54 5-11 4 1.384 802.15 802.11a,g 802.11b 802.11a,g point-to-point 802.16 (WiMAX) UMTS/WCDMA-HSPDA, CDMA2000-1xEVDO UMTS/WCDMA, CDMA2000 3G data 3G cellular enhanced.056 IS-95, CDMA, GSM 2G Indoor 10-30m Outdoor 50-200m Mid-range outdoor 200m 4 Km Long-range outdoor 5Km 20 Km 4

Organization Infrastructure mode Base stations bridge user devices and wired networks User devices moves around and access wired network through different base stations Infrastructure-less, ad-hoc mode No base stations Can only communicate with devices within the covered area Devices are self-organized into a network E.g., routing packets between user devices single-hop v.s. multi-hop 5

Characteristics of Wireless Link Limited signal strength Also decrease with distance Interference from other sources Noise, collision with other signals Multipath propagation signal reflects off objects As a result, in wireless networks, links are Often short range, unreliable, highly lossy Energy v.s. link quality 6

Signal Collision A X C A B C B Hidden terminal problem A, B can hear each other B, C can hear each other but A, C cannot hear each other, and thus are unaware of each other Signal Interfering A, B can hear each other B, C can hear each other but A, C cannot hear each other and thus interfere at B 7

IEEE 802.11 Wireless LAN 802.11b, 802.11a,802.11g,802.11n operate at different data rates all use CSMA/CA for multiple access Sense before transmitting / collision avoidance no collision detection all have base-station and ad-hoc modes Basic architecture Base stations + wireless hosts wireless hosts only (ad-hoc mode) 8

802.15 Personal Area Network Cover small area - 10m diameter Wireless keyboard, mouse, headphone Master/slaves architecture slaves send requests to master master grant access Evolved from Bluetooth specification 9

802.16: WiMAX Like 802.11 but longer range (~6 miles) city rather than a single room date rate: ~ 14Mbps Basic architecture Base stations + wireless hosts 10

Cellular Network Architecture Consists of base station mobile users wireless link Mobile switching center connect cell to telephone network / internet manage call setup handle mobility Public telephone network / Internet 11

Cellular Communication Mobile-to-BS radio spectrum is shared Two techniques to mediate the access Combined FDMA/TDMA FDMA: frequency division multiple access TDMA: time division multiple access CDMA: code division multiple access Standards 2G (voice channels): GSM 2.5G (voice/data channels): GPRS, CDMA-2000 (phase 1) 3G (voice/data channels): CDMA-2000 12

Wireless Mesh Networks Provide high-coverage, in expensive Internet service Architecture One wireless hot spot (WHS): connect WMN to Internet Mobile stations Several transit access points: connect mobile stations to WHS Single connection point to Internet Lower cost than WiFi networks 13

Mobile Ad-hoc Networks Formed in an ad-hoc manner Users are often mobile No infrastructure support Communicate through wireless link Limited energy at user device User devices also act as routers Often created for a specific purpose Military applications, battlefield network 14

Vehicular Ad-hoc Network Created for assisting drivers Offer real-time nearby traffic information e.g., alerting drivers about accidents Based on the computing and communication platforms installed on each vehicle Information are exchanged through individual vehicles, and road-side units 15

Sensor Networks To interacts with physical environments e.g., monitor volcano activity, battle field surveillance Operation in harsh environments Consists of A large number of small, low-cost sensor nodes Sense the environment, collect and report findings Also forward data packets for others Form a network of small sensors A few base stations Store data, connect to wired networks 16

RFID Identifying and tracking items An RFID system has RFID tags RFID readers Back-end database RFID tag microchip + antenna very limited memory and computing power can active (battery powered) or passive (harness energy from reader s signal) 17

Common challenges Wireless link lossy, unreliable, open Mobility Limited energy Limited computing capability 18

Mobility No mobility Users access network via the same AP Stationary wireless sensor networks Some mobility Mobile users moves around and access the network via different APs Mobile sensor networks Sensors are mobile -> routing re-construction High mobility Mobile users maintain uninterrupted network access passing many APs (cell phone) 19

Terms Home network Home agent Perform mobility support Permanent address Visited network Foreign agent Perform mobility support Could be done by the mobile itself Care-of-address 20

How to Find a Mobile Friend? Search all phone books? Call her/his parents? Check her/his website or facebook profile Expect her/him to let you know where she/he is? 21

Approaches to Handle Mobility Let routers handle it Routers propagate the permanent address Routing table includes where each mobile user is located No change on the end-systems Problem: not scalable Let end-systems handle it Direct routing get the address of FA and send messages to directly Indirect routing communication via home agent and foreign agent Registration needed (home agent need to know where is the mobile) 22

Indirect Routing Triangle routing Correspondent send messages to home address Home agent receives packets, find the visited network, and forward them to the foreign agent Foreign agent receives packets and forward them to mobile Mobile replies to correspondent directly Could be very inefficient due to the triangle 23

Moving between Networks Suppose user changes network again registers with the new foreign agent new foreign agent registers with home agent home agent update the care-of-address This is done transparently Correspondent does t need to know the change Maintain uninterrupted communication 24

Direct Routing Correspondent gets the address of FA And then forwards packets to FA FA forward packets to mobile Mobile replies directly to correspondent Benefit: overcome triangle routing problem Not transparent to the correspondent since she has to know the care-of-address What if mobile changes network again? Let the first FA (anchor FA) handle the change i.e., you always contact the anchor FA to send messages 25

Mobile IP (RFC 3344) Very similar to what we have discussed Three major components indirect routing agent discovery home/foreign agent broadcast ICMP messages registration with home agent 26

Handle Mobility in Cellular Networks Home network (e.g., T-mobile, AT&T) Home location register (HLR): database containing permanent user profile and current user location Visited network Visitor location register (VLR): database containing users currently in the network Could be home network 27

Indirect Routing in GSM home MSC consults HLR, gets roaming number of mobile in visited network mobile user HLR 4 2 home network home Mobile Switching Center VLR Mobile Switching Center visited network 3 correspondent 1 call routed to home network Public switched telephone network home MSC sets up 2 nd leg of call to MSC in visited network MSC in visited network completes call through base station to mobile 28

Handoff with Common MSC! Handoff goal: route call via new base station (without interruption) old BSS VLR old routing Mobile Switching Center new routing new BSS! reasons for handoff: " stronger signal to/from new BSS (continuing connectivity, less battery drain) " load balance: free up channel in current BSS " GSM doesn t mandate why to perform handoff (policy), only how (mechanism)! handoff initiated by old BSS 29

Handoff with Common MSC 1. old BSS informs MSC of impending handoff, provides list of 1+ new BSSs 2. MSC sets up path (allocates resources) to new BSS old BSS 1 VLR 8 Mobile Switching Center 4 2 7 5 6 3 new BSS 3. new BSS allocates radio channel for use by mobile 4. new BSS signals MSC, old BSS: ready 5. old BSS tells mobile: perform handoff to new BSS 6. mobile, new BSS signal to activate new channel 7. mobile signals via new BSS to MSC: handoff complete. MSC reroutes call 8 MSC-old-BSS resources released 30