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Wireless Security. 2005. 04. 19 교육대학원 분산시스템특론 인천대학교 민병준 032-770-8497, 011-9913-8497, [email protected] Contents. Introduction to Wireless Wireless World Wireless Threats Wireless Security Protocols and Cryptography Security Considerations for Wireless Devices

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wireless security

Wireless Security

2005. 04. 19

교육대학원 분산시스템특론

인천대학교 민병준

032-770-8497, 011-9913-8497, [email protected]

contents
Contents
  • Introduction to Wireless
    • Wireless World
    • Wireless Threats
    • Wireless Security Protocols and Cryptography
    • Security Considerations for Wireless Devices
  • Wireless Technologies and Applications
    • Cellular Networks
    • Wireless Data Networks
    • Wireless Standards and Technologies
  • Wireless Deployment Strategies
    • Implementing Wireless LANs : Security Considerations
    • Enabling Secure Wireless Access to Data
    • Real Examples from the Wireless World
    • The Wireless Future
    • Accessing Wireless LANs
cellular networks 1 4
Cellular Networks (1/4)
  • 3 Methods for Spectrum Allocation : provides access to a given frequency for multiple users
    • Frequency Division Multiple Access (FDMA)
    • Time Division Multiple Access (TDMA)
    • Code Division Multiple Access (CDMA)
  • FDMA
    • used on the initial analog Advanced Mobile Phone System (AMPS)
    • available spectrum divided into channels; each channel used for a single conversation
    • FDMA assigns channels even if no conversations are taking place - less efficient
    • only for voice transmission
    • 2G wireless technologies
      • GSM : 80%, CDMA : 11%, PDC : 5%, traditional TDMA : 2%, iDEN : 1%
  • TDMA
    • digitizes the voice signal and turns the signal into a series of short packets
    • uses a single-frequency channel for a very short time and migrates to another channel
    • voice packets can occupy different time slots in different frequency ranges at the same time
    • digital signal, better frequency allocation, support for multiple data types
    • Global System for Mobile Communications (GSM) basis
cellular networks 2 4
Cellular Networks (2/4)
  • CDMA
    • frequency hopping spread spectrum in 1940s - utilizing a wider frequency range
      • increases signal quality and connections
      • more secure, decrease the risk of the signal being detected by unauthorized parties
    • rather than dividing spectrum by time or frequency, adds a unique code onto each packet before transmission
    • the same code is used at the receiving end to enable the conversation to be reconstructed
    • stronger security, better (8-10 time than FDMA, 5 time than TDMA) frequency allocation, improved call quality, simplified system planning (by using the same frequency in every sector of every cell)
  • TDMA versus CDMA
    • TDMA advantages
      • longer battery life (less transmitter power), less expensive infrastructure, widest deployment (GSM), international roaming (GSM), data security (GSM's Subscriber Identity Module cart)
    • TDMA disadvantages
      • hard roaming handoffs, distortion (lower signal-to-noise ratio)
    • CDMA advantages
      • bandwidth efficiency, soft roaming handoffs (polls various cells and switches to the cell that offers the best signal and coverage), less distortion, strong voice security
    • CDMA disadvantage
      • more expensive, no international roaming, no SIM card
  • PDC (Personal Digital Cellular)
    • based on TDMA in 800MHz and 1500MHz
    • bandwidth efficiency, packet data, only in Japan
  • iDEN (integrated Dispatch Enhanced Network) by Nextel
    • wireless market called specialized mobile radio (SMR), walkie-talkie with a cellular phone,
cellular networks 3 4
Cellular Networks (3/4)
  • Security Threats
    • Network Operator's Security Goals
      • Authentication, Privacy, Data and voice integrity, Performance
    • Security Risks and Threats
      • Network and systems availability (DoS), Physical protection, Fraud (cloned or pirated handsets)
    • Types of Cellular Fraud
      • theft of handsets, sign up for services using false id, handset cloning,
    • Combating Fraud
      • encryption (Electronic Serial Number), blacklist (track the ESNs of stolen phones), traffic analysis, legislation
  • General Security Principles
    • Encryption - size of key : 56-bit in DES
  • GSM
    • handsets with SIM card (smart card with 32K/64K EEPROM)
    • base transceiver station
    • base station controller
    • mobile switching center
    • authentication center
    • home location register / visitor location register
    • operating and maintenance center
  • GSM security
    • authentication algorithm for handset (A3)
    • block cipher algorithm to encrypt voice and data (A5/1 or A5/2)
    • key generation algorithm (A8)
cellular networks 4 4
Cellular Networks (4/4)
  • CDMA
    • a 64-bit symmetric key (called A-Key) for authentication, no SIM card
    • why not public keys - hardware limitation, infrastructure requirements
    • Authentication
      • encryption algorithm CAVE (cellular authentication and voice encryption)
      • to minimize the risk of intercepting the A-Key in the air, dynamic value called shared secret data
      • steps
        • commence a call; MSC retrieve subscriber info from HLR, MSC generates 24-bit random number for unique challenge (RANDU); RANDU is transmitted to the phone, phone generate 18-bit AUTHU, MSC calculates AUTU which should match
    • Confidentiality
      • 64-bit Signaling Message Encryption Key (SMEKEY)
  • Shortcomings
    • no mutual authentication
    • poor security algorithms (replacing CAVE with SHA-1)
    • no consistent SIM card mechanism on handset for key storage
    • voice encryption not always
wireless data networks 1 3
Wireless Data Networks (1/3)
  • General Demands
    • faster throughput
    • more global roaming capabilities
    • interoperability with internet
  • Wireless Data Networks
    • Cellular Digital Packet Data (CDPD)
    • Mobitex
    • General packet Radio Service (GPRS)
  • Cellular Digital Packet Data (CDPD)
    • standard developed in US in 1990s
      • offering wireless data services using AMPS (Advanced Mobile Phone Service) infrastructure
    • advantages
      • speed (19.2 Kbps), TCP/IP based (compatible with Internet), quick call setup
    • architecture
      • similar to wireless voice networks
      • mobile end system ... mobile database stations - mobile data intermediate system - Internet (firewall)
    • security
      • similar to wireless voice network (CDMA) : unique id called NEI (Network Entity Identifier)
      • no tamper-resistant hardware such as SIM
      • Diffie-Hellman key exchange
      • vulnerabilities
        • no mutual authentication, local key storage (no SIM to store NEI)
wireless data networks 2 3
Wireless Data Networks (2/3)
  • Mobitex
    • wireless data technology developed by Ericsson in 1980s
      • operate in one of 4 frequency families (80MHz, 400MHz, 800MHz, 900MHz)
      • 8Kbps rate, 512-bytpe block transmission
      • royalty-free license
    • architecture
      • peer-to-peer ... base station - local switch - regional switch - national switch / Internet
    • application of the network : Blackberry wireless e-mail pager offered by Canadian-based Research in Motion (RIM)
      • RIM device (32-bit Intel 386 processor, 2MB flash mem, 304Kb static RAM) security model focused on MS outlook & Lotus cc:Mail
    • RIM security architecture
      • desktop - mail server - firewall - Internet - mobile network ... RIM handheld
    • Mobitex vs. CDPD (Mobitex will outlast CDPD)
      • network infrastructure (eliminating AMPS hardware), strong industry association (Mobitex Operators Association led by Ericsson), greater coverage
wireless data networks 3 3
Wireless Data Networks (3/3)
  • General Packet Radio Service (GPRS)
    • GSM developed in 1990s
      • packet-based
        • compatibility with the Internet
        • always-on connection
        • efficient networks
    • higher throughput
      • use many time slots in parallel
      • data split into chunks and sent simultaneously on multiple channels to a handset
    • handsets
      • Class A terminal (support GPRS and GSM and the simultaneous operation of both, e.g., email + voice)
      • Class B terminal (support GPRS and GSM but not simultaneously)
      • Class C terminal (only GPRS)
    • architecture
      • base station - base station controller - SGSN - HLR / GGSN - Internet
        • SGSN : data router (service GPRS service node)
        • GGSN : gateway GPRS Support Node
        • other network components : charging gateway, border gateway, DNS, lawful interception gateway, firewall and network management stations
    • security issues
      • DoS against GGSN
      • IP address spoofing
      • GGSN - Internet - VPN server - corporate LAN
        • not end-to-end security(SGSN-GGSN), added cost(VPN), trust issue (enterprise - mobile operator)
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