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

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 –L&C 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 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)

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