Physical Contact in AdHoc Wireless Network

1
Physical Contact in Ad-Hoc Wireless Network

• Nie Pin
• 27.10.2006

2
Agenda

• Introduction
• Assumptions on Ad-Hoc Wireless Network during the
  First Connect
• Constraints on mobile devices
• Attack Models
• Principles of Physical Contact
• Out-Of-Band (OOB) solutions
• Evaluation
• Conclusion

3
Introduction

• First Connect
• Initial setup of a security association among two
  or more devices for subsequent secure
  communication. Typical case pairing of two
  devices, agreement signing between two parties.
• Physical Contact
• Negotiating and exchanging process within a
  limited scope, between two parties. (OOB)
• Basic perceivability of the surroundings (users
  role)
• Out of Band (OOB)
• A separate communicating band (auxiliary channel)
  other than the one used for the subsequent
  communications, for exchanging security
  parameters (e.g. transmitting authentication
  data) or control information

4
Assumptions

• Direct talk
• One-to-One communication style
• Demonstrative Identification (DI)
• Authentication and confirmation
• Limit the control range, reduce interferences
• No trusted third party
• No valid assertion, token, rumor and
  recommendation
• No previous context
• No history and experience
• Security Transient Association
• Not necessary, but likely in practice, better to
  include

5
Constraints

• User Interface
• Input
• Keypad, handwriting, microphone, camera,
  biometric detectors
• Output
• Sticker (i.e. label), LED, beeper, LCD display
• Computing Power and Memory
• Weak CPU (Intel PXA255 400MHz, bus 200MHz)
• Little memory (HP iPAQ Pocket PC 2215 96MB,
  Nokia 6822 3.5MB internal memory)
• Battery Consumption
• Limited on electrical power (Nokia N95 Talk
  time2.5-3.5 hours, PDA Talk time4-6 hours)

6
Attack Models

• Active Attacks
• Denial-of-Service (DoS) attack
• Block the target by flooding it with numerous
  requests
• Considering the battery limit, it turns to be
  sleep deprivation torture.
• Interference attack
• Create too much strong noises to disable the
  detection at the receivers side
• Man-in-the-middle (MITM) attack
• Modifying data streams, inserting and deleting
  (break the integration)
• Playback of data, e.g. reflection attack and
  replay attack.
• Passive Attacks
• Eavesdropping, a step for further attacking

7
Principles of Physical Contact

• Bootstrap
• Imprinting, what should be bound or exchanged for
  subsequent secure communication?
• Proximity Detection
• Fulfill the DI requirement
• Presence Confirmation
• Derive from DI
• Capture intention and set location restriction
• Pre-authentication
• Control Information or security factors exchange
  by using OOB
• Flexibility
• The solution can be carried out in many forms or
  OOBs to fit the constraints of different devices

8
Out-Of-Band (OOB) solutions

• Authenticated Strings
• Use commitment schemes to exchange the
  commitment, containing the keys and a hidden
  value
• Strings/numeric Comparison or Passkey-based
• User acknowledges the check values on both
  devices or input the value (a shared secret) to
  the other devices
• Human knowledge based
• Radio, Infrared and ultrasound
• Special transmitter and receiver for the channel
• Location limited channel (LLC) distance binding
• Closest proximity assumption is the necessary
  condition
• Visual Channel
• Camera needed, display (e.g. LCD or LED) needed
• Computing intensive analyzing algorithms
• Two examples SiB and VIC (DH-IC)
• Audio Channel
• LC with the same basic idea as SiB
• Biometrics Channel
• E.g. Grip pattern, fingerprint, voice spectrum

9
Evaluation

• Advantages
• Benefits
• Pre-authentication, DI, MitM attack prevention
• Flexibility
• Unidirectional authentication and mutual
  authentication
• Disadvantages
• Algorithms complexity
• E.g. image processing, light signals processing,
  distance measurement, Integrity verification
• Extra assumptions or overhead on devices and
  environment
• Channel carrier (e.g. transmitter, receiver,
  detector or camera, LED)

10
Evaluation (2)

• Human knowledge / biometric based
• Simple, but needs user operation (e.g. compare or
  input) as the auxiliary authentication channel
• Radio, infrared and ultrasound
• Fool prove
• High requirement on distance measuring
• Special modules needed on the devices
• Visual channel
• Easy to use
• Algorithm complex and computing intensive

11
Conclusion

• Balancing game
• Tradeoff between usability (human involved
  degree) and complexity (algorithms simulate human
  perceivability, e.g. seeing, touching, feeling)
• Tradeoff between security and efficiency,
  execution time (e.g. integrity verification)
• Fitting specific situations (applications scope)
• One way authentication for ad-hoc services in
  public places
• Lower the requirements on SPs equipments (e.g.
  SCgtPasskey, SiBgtVIC)
• Mutual authentication for peer-to-peer
  communications
• Make full use of popular equipments or functions
  on mobile devices (e.g. SC, SiB)

12
Acknowledgement

• Thanks for the comments and suggestions from
  Prof. K. Nyberg , Prof. N. Asokan, Jukka Valkonen
  and Vesa Vaskelainen ?