1. Design of Physically Unclonable Functions Using FPGAs
CPRE 583
Michael Patterson, Aaron Mills 1

2. What is a PUF? Hardware hash function Uniquely identify a device
“Impossible” to reverse engineer
Modeling attacks, power spectrum analysis...
Applications: RFID, Chip Authentication, Etc. 2

3. Delay-Based PUF Types Butterfly PUF
Requires feedback loops to be identical 3

4. Delay-Based PUF Types Arbiter PUF
Again, issue: each “race track” must be identical
Tunable delay, constrain the synthesis placement, etc... 4

5. Our Design
16 bit challenge, 8 bit response 5

6. Our Design Rationale Challenge partitioning Number of ROs
Counter value
Other comments 6

7. RO in vhdl signal ros : std_logic_vector(4 downto 0);
attribute keep: boolean;
attribute keep of ros: signal is true; 7

8. Properties of a good PUF
Consistency
Uniqueness
One-to-One

9. “Consistency” Testing
One PUF, One Challenge:
PUF is given the same 16-bit challenge 32 times
repeated for 128 randomly generated challenges.
the percentage of responses that differ will be calculated
the ideal value is a 0 percent change.

10. “Consistency” Results
The 8-bit response was correct percent of
the time.

11. “Uniqueness” Testing One PUF, different challenges
A single PUF is given 1024 different challenges consisting of a Gray Code pattern (a series of numbers that tours unique data values bychanging only one bit at a time).
The average hamming distance between adjacent responses will be calculated.
ideal average hamming distance is 50 percent.

12. “Uniqueness” Results
On average, 2.88 bits change in the response for a one
bit change in input.

13. “One-to-One” Testing Different PUFs, one challenge
Different PUFs given the same series of challenges.
The average hamming distance between responses is calculated.
ideal average hamming distance is 50 percent.

14. “One-to-One” Results
On average, percent of the bits are different between responses of two different PUFs to the same challenge.

15. Temperature Stability
Why is considering temperature important?
Linear approximation:
ρ(T) = ρ0[1 + α(T − T0)]

16. Temperature Stability
Testing
Same format as Consistency test
Every 5C from 10C to 65C

17. Temperature Stability
Results
But...most errors caused by a few inputs
Response Bit 1 2 3 4 5 6 7
Ham. Distance (%)
0.3
0.1
0.6
0.2

18. Hard Macros
Why are hard macros useful?
Issues...

19. Future Work Hard Macro Usage Post processing to improve results
Repeat same challenge several times
Large input size for testing to increase statistical significance of results
Research properties of different input patterns
Optimize design to consume less space on the fpga
Multi-phase calculation

20. References
1. An Analysis of Delay Based PUF Implementations on FPGA, Sergey Morozov, Abhranil Maiti, and Patrick Schaumont
2. Physical Unclonable Functions for Device Authentication and Secret Key Generation, G. E. Suh and S. Devadas.
3. B. Gassend, D. Clarke, M. van Dijk, and S. Devadas. Delay-based circuit authentication and applications. 20

21. References
4. J. Guajardo, S. Kumar, G.-J. Schrijen, and P. Tuyls. Physical unclonable functions and public-key crypto for fpga ip protection.
5. S. Kumar, J. Guajardo, R. Maes, G.-J. Schrijen, and P. Tuyls. Extended abstract: The butterfly puf protecting ip on every fpga.
6. M. Majzoobi and F. Koushanfar. Time- bounded authentication of fpgas.
7. G. E. Suh and S. Devadas. Physical unclonable functions for device authentication and secret key generation.