Physically Restricted
Authentication with
Trusted Hardware
Michael Kirkpatrick, Elisa Bertino
Department of Computer Science
4th Annual Workshop on Scalable
Trusted Computing (STC)
Agenda
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Introduction
Physically Unclonable Functions (PUFs)
Design Requirements
Protocols
Future Work
Conclusions
Agenda
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Introduction
Physically Unclonable Functions (PUFs)
Design Requirements
Protocols
Future Work
Conclusions
Introduction
New York
Miami
Chicago
Los Angeles
Introduction
• 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
Agenda
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Introduction
Physically Unclonable Functions (PUFs)
Design Requirements
Protocols
Future Work
Conclusions
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
PUFs
Counter
C
Compare
Counter
C
1/0
R
Agenda
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Introduction
Physically Unclonable Functions (PUFs)
Design Requirements
Protocols
Future Work
Conclusions
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
Agenda
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Introduction
Physically Unclonable Functions (PUFs)
Design Requirements
Protocols
Future Work
Conclusions
Protocols
• Installation & Commitment
▫ Secret sharing for symmetric key K
▫ Each administrator gets one Ci
▫ Xi = Ri  bi  GCD(Xi,N) = 1
Protocols
• Authentication
▫ C picks a random r
▫ I* indicates a random set of Ci
▫ Accept if y2 = +/- r2 X12 ... Xk2
Agenda
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Introduction
Physically Unclonable Functions (PUFs)
Design Requirements
Protocols
Future Work
Conclusions
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
Agenda
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Introduction
Physically Unclonable Functions (PUFs)
Design Requirements
Protocols
Future Work
Conclusions
Conclusions
• 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