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

Agenda Challenges in Hardware Security What is PUF ? Applications of PUFs Classification of PUFs PUF Circuits Summery References Hardware Security and Trust, CE, SUT

Challenges=>Conventional Authentication Conventional Authentication Schemes Need to store keys Power and area consuming Hardware Security and Trust, CE, SUT

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 Hardware Security and Trust, CE, SUT

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 Hardware Security and Trust, CE, SUT

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

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 Hardware Security and Trust, CE, SUT

Types of PUFs Optical PUFs Coating and Acoustic PUFs Silicon PUFs(SPUF) timing and delay information easy integrate into ICs

Applications of PUF 1) Low cost authentication[1] Hardware Security and Trust, CE, SUT

Applications of PUF 2) Cryptographic Key Generator[1] *ECC=Error Correction Code Hardware Security and Trust, CE, SUT

Applications of PUF 3) Software Licensing and Anonymous Computation[3] *CPUF=Controlled PUF Hardware Security and Trust, CE, SUT

Applications of PUF 3) Software Licensing and Anonymous Computation Hardware Security and Trust, CE, SUT

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

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 Hardware Security and Trust, CE, SUT

PUF Circuits Arbiter PUF[4] Hardware Security and Trust, CE, SUT

PUF Circuits Arbiter PUF delay paths with the same layout length Simple->attackers can construct a timing model Hardware Security and Trust, CE, SUT

PUF Circuits construct a k-bit response one circuit can be used k times with different inputs duplicate the single-output PUF circuit Hardware Security and Trust, CE, SUT

PUF Circuits Feed Forward Arbiter PUF Hardware Security and Trust, CE, SUT

PUF Circuits Lightweight Secure PUF[7] Hardware Security and Trust, CE, SUT

PUF Circuits Ring Oscillator PUF [1] Hardware Security and Trust, CE, SUT

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 Hardware Security and Trust, CE, SUT

PUF Circuits Ring Oscillator PUF environmental conditions Choose ring oscillator pairs, whose frequencies are far apart=>remove key generation error Hardware Security and Trust, CE, SUT

PUF Circuits SRAM SRAM PUF[5] Hardware Security and Trust, CE, SUT

PUF Circuits Butterfly PUF[6] Hardware Security and Trust, CE, SUT

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

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):1198-1210, 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

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