1. Physically Restricted Authentication with Trusted Hardware Michael Kirkpatrick, Elisa Bertino Department of Computer Science 4 th Annual Workshop on Scalable Trusted Computing (STC)

2. Agenda Introduction Physically Unclonable Functions (PUFs) Design Requirements Protocols Future Work Conclusions

3. Agenda Introduction Physically Unclonable Functions (PUFs) Design Requirements Protocols Future Work Conclusions

4. Chicago Los Angeles Miami New York Introduction

5. Full access provided to trusted devices ▫Fine-grained access control at application layer Permit mobility of the device Mitigate insider threats Minimize computation overhead ▫Applicable for low-power embedded devices

6. Agenda Introduction Physically Unclonable Functions (PUFs) Design Requirements Protocols Future Work Conclusions

7. PUFs Functions ▫Given challenge C, provides response R ▫Output is consistent for same input Unclonable ▫Cannot be predicted, controlled, or duplicated Physical ▫HW instance resolves non-determinism

8. PUFs Counter Compare 1/0 C R C

9. Agenda Introduction Physically Unclonable Functions (PUFs) Design Requirements Protocols Future Work Conclusions

10. Design Requirements Avoid chain-of-trust assumptions ▫No PKI Zero-knowledge proof is critical ▫PUF behavior must be protected ▫Adaptation of Feige-Fiat-Shamir Intractability of modular square roots

11. Agenda Introduction Physically Unclonable Functions (PUFs) Design Requirements Protocols Future Work Conclusions

12. Protocols Installation & Commitment ▫Secret sharing for symmetric key K ▫Each administrator gets one C i ▫X i = R i  b i  GCD(X i,N) = 1

13. Protocols Authentication ▫C picks a random r ▫I* indicates a random set of C i ▫Accept if y 2 = +/- r 2 X 1 2... X k 2

14. Agenda Introduction Physically Unclonable Functions (PUFs) Design Requirements Protocols Future Work Conclusions

15. Future Work Implementing PUFs ▫Trade-offs of size, performance, randomness ▫What vulnerabilities exist? Designing new protocols ▫PUF-based signatures ▫Zero-knowledge proofs without intractability assumptions Additional applications

16. Agenda Introduction Physically Unclonable Functions (PUFs) Design Requirements Protocols Future Work Conclusions

17. PUFs can enforce physical access control restrictions ▫Can be used where TPMs cannot Protection of PUF behavior is vital PUF-specific protocols and applications can help the technology grow