1. Physical Unclonable Functions
Farzane Salehi Minapour
Aida Miralaei
MohammadKazem Taram
Department of Computer Eng.
Sharif University of Technology
Spring 2014

2. Agenda Challenges in Hardware Security What is PUF ?
Applications of PUFs
Classification of PUFs
PUF Circuits
Summery
References
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3. Challenges=>Conventional Authentication
Conventional Authentication Schemes
Need to store keys
Power and area consuming
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4. Challenges => Store Secrets.
Challenges => Store Secrets
Conventional approach to embed secure secrets in IC
Non-volatile memory(ROM, Fuse, Flash or EEPROM)
Battery-backed RAM
Non-volatile memory technologies are often vulnerable to invasive and non-invasive attack
Adversaries can physically extract secret keys from EEPROM while processor is off
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5. Challenges=>expensive tamper proof packs
Storing digital information in a device in a way that is resistant to physical attacks is difficult and expensive.
IBM 4758
Tamper-proof package containing a secure processor which has a secret key and memory
Tens of sensors, resistance, temperature, voltage, etc.
Continually battery-powered
~ $3500 for a 99 MHz processor and 128MB of memory
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6. Challenges=>Power and Area
Power and Area are critical
RFID tag can afford a maximum of 2000 gates for security features
Passive RFIDs
A good cryptographic primitive should be
lightweight, occupy little area on silicon and
should have very low power consumption.
Hardware Security and Trust, CE, SUT

7. What is PUF? Physical Unclonable Function (PUF)
Process variations can be turned into a feature rather than a problem
Variation is inherent in fabrication process
Unique for each physical instance
Hard to remove or predict
Relative variation increases as the fab process advances
Non-silicon PUFs
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8. Types of PUFs Optical PUFs Coating and Acoustic PUFs
Silicon PUFs(SPUF)
timing and delay information
easy integrate into ICs

9. Applications of PUF 1) Low cost authentication[1]
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10. Applications of PUF 2) Cryptographic Key Generator[1]
*ECC=Error Correction Code
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11. Applications of PUF 3) Software Licensing and Anonymous Computation[3]
*CPUF=Controlled PUF
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12. Applications of PUF 3) Software Licensing and Anonymous Computation
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13. Applications of PUF 4) Random Number Generation [2]
0.1% of all challenges do not return a consistent response
These meta-stable challenges generate responses which can vary unpredictably

14. Classification of PUFs
Strong PUFs
Large number of challenge response pairs
IC identification and secret key generation
E.g arbiter PUF and feed forward arbiter
Weak PUFs
Limited number of challenge response pairs (sometime just single)
Secret key generation
E.g SRAM PUF and butterfly PUF
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15. PUF Circuits
Arbiter PUF[4]
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16. PUF Circuits Arbiter PUF delay paths with the same layout length
Simple->attackers can construct a timing model
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17. PUF Circuits construct a k-bit response
one circuit can be used k times with different inputs
duplicate the single-output PUF circuit
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18. PUF Circuits Feed Forward Arbiter PUF
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19. PUF Circuits Lightweight Secure PUF[7]
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20. PUF Circuits Ring Oscillator PUF [1]
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21. PUF Circuits Ring Oscillator PUF Easier Implementation
No need for careful layout and routing
Slower, Larger, more power to generate bits
Better for FPGAs and secure processors
Hard to generate many challenge response pairs
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22. PUF Circuits Ring Oscillator PUF environmental conditions
Choose ring oscillator pairs, whose frequencies are far apart=>remove key generation error
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23. PUF Circuits SRAM
SRAM PUF[5]
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24. PUF Circuits
Butterfly PUF[6]
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25. Summery
PUFs are innovative circuit primitives that extract secrets from physical characteristics of integrated circuits (ICs)
PUFs can enable low-cost authentication of individual ICs
Generate volatile secret keys for cryptographic operations both symmetric and asymmetric cryptographic operations
PUF applications and circuits
Hardware Security and Trust, CE, SUT

26. References
[1] Suh, G.E., Devadas, S.: Physical unclonable functions for device authentication and secret key generation. In: Design Automation Conference, pp. 9{14. ACM Press, New York, NY, USA (2007)
[2] C. W. O’Donnell, G. E. Suh, and S. Devadas . PUF-based random number generation. In MITCSAIL CSG Technical Memo 481, November 2004
[3] Gassend, Blaise, et al. "Controlled physical random functions and applications." ACM Transactions on Information and System Security (TISSEC) 10.4 (2008): 3.
[4]   J.W. Lee, D. Lim, B. Gassend, G. E. Suh, M. van Dijk and S. Devadas, “ A technique  to build a secret key in integrated circuits with identification and authentication applications”, in Proceedings of the VLSI Circuits Symposium, June 2004. 
[5]    D. E. Holcomb, W. P. Burleson, and K. Fu, “  Power-up SRAM State as an Identifying Fingerprint and Source of True Random Numbers”,  in  IEEE Transactions on Computers, 58(9): , 2009.
[6] S. S. Kumar, J. Guajardo, R. Maes, Geert-Jan Schrijen  and P. Tuyls,  “Extended Abstract: The Butterfly PUF Protecting IP on every FPGA”, in  IEEE International Workshop on Hardware-Oriented Security and Trust, HOST 2008.
[7] M. Majzoobi, F. Koushanfar and M. Potkonjak, “Lightweight Secure PUFs”, in IEEE International Conference on Computer-Aided Design, 2008
Hardware Security and Trust, CE, SUT

27. Thanks