Manageable Identities MID: Using Trusted SIMBased WLAN Authentication

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Manageable Identities (MID) Using Trusted
SIM-Based WLAN Authentication

• Selim Aissi, Ph.D.
• Intel Research Development
• Intel Corporation
• October 16, 2003

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Intel RD Wireless Vision
Identities
All Devices Can Present Multiple Identities
Identities Consistent Manageable Across Devices
Easy, Trusted, Consistent Access with Any
Appropriate Identity
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Agenda

• Problem Statement
• SIM Based Authentication
• GSM/GPRS Network
• Applied to WLAN
• SIM Attachment to Open Platforms
• Attachment Options
• Security Issues
• Solutions
• Trusted SIM Access

This presentation contains information on
products in the design phase of development. The
information here is subject to change without
notice. Do not finalize a design with this
information.
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WWAN - WLAN Convergence
Problem Statement
Signal
Data
SGSN
BSC/RNC
GGSN
2.5/3G CORE
2.5/3G RAN
AuC
H/VLR
BTS/Node B
Open platforms do not have a consistent, easy,
and trusted method to access WWAN and WLAN
networks
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What is SIM?
SIM based Authentication

• Subscriber Identity Module (SIM)
• Uniquely represents the identity of the
  subscriber
• Required in GSM/GPRS and optional in CDMA
  networks
• Provides
• Tamper Resistant Environment
• Protected Execution
• Protected Storage
• Form and Function Defined by
• 3GPP/ ETSI GSM 11.11, 11.12, 11.18
• WAP Forum WAP-260-WIM-20010712-a
• ISO 7816- 1,2,3,4,

ID-000 Style
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Role of SIM in GSM/GPRS
SIM based Authentication

• Hardware-based storage of secrets
• Operator provisioned user identity and keys
• User data
• Hardware protected execution environment
• GSM authentication algorithms
• User subscription identity and data migration
• Enables User to switch client devices while
  retaining their services

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Authentication in GSM/GPRS
SIM based Authentication
IMSI/TMSI International/Temporary Mobile
Subscriber Identity
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Applied to WLAN
SIM based Authentication
EAP-SIM
GSM MAP/SS7
PEAP (TLS)
EAP
802.1X
RADIUS
Optional
802.3 / TCP/IP
802.11 (TKIP,.11i)
Note EAP - Extensible Authentication Protocol,
RFC 2284, 2284bis
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SIM Usage for WLAN
SIM based Authentication

• EAP-SIM
• EAP Protocol method that allows SIM credentials
  to be used over EAP
• Useful for WLAN or any EAP based access control
  network
• Modifies GSM Authentication protocol over EAP
  channel
• EAP-SIM features
• Mutual Authentication
• Message Authentication and Integrity Protection
  (MACs)
• Re-authentication
• Partial Identity Privacy
• Key Derivation and data privacy
• EAP-AKA
• EAP method defined for USIM authentication also
  called AKA (Authentication and Key Agreement)
• Note CDMA networks have a similar R-UIM
  definition (Removable User Identity Module)
• No EAP method defined yet

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WPA (Wi-Fi Protected Access) and EAP-SIM
SIM based Authentication

• WPA
• Adds strong authentication using 802.1X and EAP
  methods
• Enhances encryption WEP (Wireless Equivalence
  Privacy) to TKIP (Temporal Key Integrity
  Protocol)
• EAP-SIM is an EAP method
• Applies GSM SIM authentication process to WLAN
• Intel Centrino mobile technology supports WPA

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Value of SIM Authentication in WLAN
SIM based Authentication

• Service limited to authorized Subscribers
• SIM benefits to the user
• Facilitates transparent Login
• Common subscriptions and billing
• SIM is trusted by operator
• Customer ownership, proven security
• Reuse of existing authentication billing
  infrastructure
• Preserves SIM investments

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SIM Re-Use in Open Platforms
SIM re-use in WLAN provides Single Bill Roaming
and Cell Phone like user experience
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SIM Security in Open Platforms
SIM re-use in open platforms
SGSN
Base Station
HLR / AuC
Over Air
Authentication
RAND Kc
RAND
RAND
RAND Kc SRES
Closed System
SRES Kc
SRES
SRES
HLR / AuC
Access Point
AAA
Over Air
Authentication
RAND Kc
RAND
RAND
RAND Kc SRES
SRES Kc
SRES
Open System
SRES

• Threats
• Open data path issues SRES, Kc are are visible
• Notebook is open to Viruses, Trojan Horses, and
  MiM attacks

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Weakness of SIM
SIM re-use in open platforms

• Attack on secret key Ki (SIM cloning)
• COMP 128-1 algorithm can be cracked by collecting
  triplets (RAND, SRES, and Kc) to deduce Ki
• Relatively easy in WLAN environment with open
  platforms
• Denial of service
• Repeated attempts to collect triplets may lock
  out SIM
• Attack on integrity of SIM data
• SIM data is protected by PIN code
• A Trojan Horse or Virus can eavesdrop on internal
  communications to discover PIN

Risks of such attacks are low in cellular systems
because of the closed nature of the cellular
system
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Solving Open Data Path Issues
SIM re-use in open platforms

WWAN and
WiFi
WWAN and
WLAN
networks

• Solutions for solving open data paths
• Trusted hardware execution environment
• Encrypted tunnel for Path A
• End-to-end encrypted tunnel over Paths A and B

Network Application
Network Application

• Addressed by standards bodies
• EAP-SIM
• PEAP

Network Client
Network Client
Network
Network
Interface
Interface
Interface to Device
Interface to Device
with Credential
with Credential
(BUS, Drivers, etc.)
(BUS, Drivers, etc.)
Open Platform
Open Platform
Path A
Path B
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Encrypted Tunnel for SIM Access
SIM re-use in open platforms
WLAN-SIM
EAP-SIM
PEAP
Encrypted Tunnel
EAP
ISO 7816-4 APDUs
802.1X
802.11

• Note
• APDU Application
• Protocol Data Unit
• (ISO 7816 Part 4)

Not all protocol termination points shown
Work In Progress for improved security
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Summary

• SIM Re-Use for WLAN authentication is
  advantageous to operators
• Preserves existing infrastructure investment
• SIM authentication is trusted
• Single bill for WWAN and WLAN services
• Requires addressing possible open platform
  threats
• Mitigation through trusted platform elements and
  encrypted data tunnels

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Thank you!
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The Alphabet Soup

• AAA Authentication Authorization Accounting
• AKA Authentication and Key Agreement
• AP Access Point
• APDU Application Protocol Data Unit (ISO 7816
  Part 4)
• APDU-TLS TLS Protocol adaptation for protecting
  APDUs on SIM-ME interface
• AuC Authentication Center
• BSC / RNC Base Station Controller / Radio
  Network Controller (under the UMTS system)
• BT SAP Bluetooth SIM Access Profile
• BTS Base Transceiver Station
• EAP Extensible Authentication Protocol, RFC
  2284, 2284bis
• EAP-SIM - SIM based EAP method for authentication
• EAPOL EAP Over LAN. EAP Message encapsulation
  and extensions for 802.1X operation
• GGSN / SGSN Gateway GPRS Support Node / GPRS
  Support Node
• GPRS General Packet Radio Service
• GSM Global System for Mobile Communication
• HLR / VLR Home Location Register / Visitor
  Location Register
• IMSI / TMSI International Mobile Station
  Identity / Temporary Mobile Subscriber
  Identification
• Kc / Ki Cipher Key / Subscriber Authentication
  Key
• MAP GSM Mobile Application Part