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Wireless Communication Overview
• GSM
• GSM Properties
– cellular radio network
– digital transmission up to 9600 bit/s
– roaming (mobilität among different network providers, international)
– Good transmission quality (error recognition and correction)
– scalable (große Teilnehmerzahlen möglich)
– worldwide 900 million subscribers
– Europe : over 300 million subscribers
– security mechanisms provided (authentication, authorisation, encryption)
– good usage of resources (frequency- and time-multiplex)
– integration with ISDN and analogue telephone network
– standard (ETSI, European Telecommunications Standards Institute)
• GSM
GSM Security Requirements
Network provider‘s view
• correct Billing: authenticity of the user
• no misuse of the service, correct billing of content-usage
• efficiency: no more bandwidth needed for security, no long delays (user acceptance), cost-efficient
User‘s view
• confidentiality of communication (voice and data)
• privacy, no profiles of the movements of the users
• connection with authentic base station
• correct billing
Content provider‘s view
• correct billing
• GSM
Overview of GSM Security Services
Smartcard-based authentication of the user
• Identification of the through worldwide unique name IMSI
• Algorithm A3 for authentication is not public,
Confidentiality on the radio link:
• Algorithms: up to 7 A5 variants
• unique, permanent subscriber key Ki and
dynamicly generated communication keys Kc
Anonymity:
• use of temporary identities
• GSM-Architecture
• GSM-Architecture
• GSM Security
• GPRS: General Packet Radio Service
• Properties
– Packet mode service (end-to-end)
– Data rates up to 171,2 kbit/s (theoretical), effectively up to 115 Kbit/s
– Effektive und flexible Verwaltung der Luftschnittstelle
– Adaptive channel coding
– Standardised interworking with IP- and X.25 networks
– dynamic resource sharin with the „classic“ GSM voice services
– advantage: billing per volume, not per connection time
– GPRS Security Mechanisms
• Security in GPRS eng very similar to GSM
– Authentification through SGSN with Challenge-Response
– Use of temporary identities (managed through SGSN)
– Encryption algorithm A5/3 (GEA3)
– But: no end-to-end encryption
– Key generation and managment as in GSM
– No authentication and confidentiality of signalling messages within the signalling network
• UMTS
• UMTS properties
– packet oriented, all-IP, 2-10 Mb/s throughput,
– Rich Telephony (voice with video, sound),
– audio-, video-streaming (movies etc.),
– better QoS, more user control,
– video-conferencing as killer application??
– worldwide roaming
– It is basically a merge of mobile telephony, wireless and paging technologies into a common system
– Support of different carrier systems
• Real time / not real time
• Line switching / packet switching
– roaming between UMTS and GSM as well as satellite networks
– asymmetric data rates for up-link/down-link
• UMTS Cell Structure
• UMTS Service Concept
• UMTS Service Concept
– Virtual Home Environment (VHE): services freely configurable through user
– service quality and according cost can be chosen
– dynamic Anpassung an die Verbindung
• UPT: Universal Personal Telecommunication Service
– One subscriber number for multiple devices (call management)
– virtual mobility of the terrestric network
• UMTS Security
Adaptation of GSM security
• Confidentiality of the user identity
• Authentication of the user towards the network
• Encrypted communication over the radio link,
• SIM card as personal security module with authentication of the user towards the SIM card USIM (UMTS Subscriber Identity Module)
• UMTS Security
• UMTS Extensions
– extended UMTS Authentification and key agreement
home network authenticated towards the user,
sequence numbers: prevents replay of authentication data,
keyed MAC
– Integrity of control data:
control data during connection establishment are secured with MAC
– USIM controlled use of keys
the USIM provides new authentication if the encrypted data exceed a certain volume
– Periodic key renewal
– Integrity and confidentiality of communication data:
128-bit communication key, MACs for integrity
• UMTS Problems
Problems
– Interoperability between 2G, 2.5G und 3G mobile networks
– different security features: what does it mean in case of roaming between old and new networks?
• Wireless Network Infrastructures
• Wireless local area networks (WLAN) and wireless personal area networks (PAN)
• advantages
– flexibility
– Ad-hoc networks easy to establish
– No cables
– robustness
• disadvantages
– Comparatively low data rates (11 Mbit/s or 54 Mbit/s)
– Higher vulnerability on the transmission page link in comparison to cabled local area networks
– no international standards for frequency bands
– security