Physical Contact in Ad-Hoc Wireless Network

Nie Pin

27.10.2006

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

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

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

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

time:2.5-3.5 hours, PDA – Talk time:4-6 hours)

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

receiver’s 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

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

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– L&C with the same basic idea as SiB

• Biometrics Channel– E.g. Grip pattern, fingerprint, voice spectrum…

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)

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

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 SP’s equipments (e.g.

SC=>Passkey, SiB=>VIC)– Mutual authentication for peer-to-peer

communications• Make full use of popular equipments or functions on mobile

devices (e.g. SC, SiB)

Acknowledgement• Thanks for the comments and suggestions from

Prof. K. Nyberg , Prof. N. Asokan, Jukka Valkonen and Vesa Vaskelainen