MIXED SIGNAL LETTER Integrated circuit design for physical unclonable function using differential amplifiers Byong-Deok Choi • Tae-Wook Kim • Mun-Kyu Lee • Ki-Seok Chung • Dong Kyue Kim Received: 15 March 2009 / Revised: 2 November 2010 / Accepted: 12 November 2010 / Published online: 28 November 2010 Ó Springer Science+Business Media, LLC 2010 Abstract A physical unclonable function (PUF) based on process variations on silicon wafers is a very promising technology which finds various applications in identifica- tion and authentication, but only a few integrated circuits have been reported so far. As those circuits are vulnerable to power supply noises, switching noises and environ- mental variations, they lead to a reliability issue such as time-varying or metastable responses. To resolve this issue, this letter proposes a new integrated circuit design for PUFs using differential amplifiers. The feasibility of the proposed circuit has been theoretically analyzed and vali- dated through HSPICE simulations for the previous and proposed circuits. Keywords Physical unclonable function  Process variation  Differential amplifier  Identification  Authentication 1 Introduction It is well known that even identical circuits manufactured in the same process have slightly different physical prop- erties due to variations in the process. Thus circuits with the same layout may generate outputs with unpredictable deviations. If the outputs of the circuits provide a sufficient level of randomness and they are unique to each of the circuits, then these circuits may be viewed as hardware fingerprints for each chip and they are called physical unclonable functions (PUFs) [1, 2]. Because PUFs can play a role of a unique identifier for each chip without any expensive external programming or special manufacturing step [3], they can be used for low-cost identification applications including radio frequency identification (RFID). Another attractive feature of PUFs is that they are naturally resistant to cloning attacks, that is, the ID of a chip cannot be cloned even if an adversary builds an illegal copy of the chip. More important applications of PUFs can be found in secret key management [4]. Whereas conventional tech- niques of storing keys in a nonvolatile memory are vul- nerable to physical tampering attacks such as micro- probing, laser cutting, and so on, a key originated from a PUF prevents these attacks because it is intrinsically invisible to the outside of the chip. This advantage of PUFs can be applied to secure data storage and content protec- tion, e.g., in pay TV where the data is encrypted and should be decrypted by only an owner of a proper hardware key. PUF-based cryptographic keys can also be applied to access control and device authentication [5]. Encryption and authentication using PUFs can be combined to provide more sophisticated applications such as secure financial transaction, secure wireless communication, and IP distri- bution management [6, 7]. In order to use the PUF in the above applications, we should guarantee that the PUF provides sufficient ran- domness in the bits they generate and diversity among chips. Also, these bits should be unique to each chip and resistant to variations in operating conditions. It should be noted that the PUF is different from the true or pseudo random number generator (TRNG or PRNG), in that it B.-D. Choi  T.-W. Kim  K.-S. Chung  D. K. Kim (&) Department of Electronic Engineering, Hanyang University, 17 Haengdang-Dong, Seong dong-Gu, Seoul 133-791, Korea e-mail: dqkim@hanyang.ac.kr M.-K. Lee School of Computer and Information Engineering, Inha University, Incheon 402-751, Korea 123 Analog Integr Circ Sig Process (2011) 66:467–474 DOI 10.1007/s10470-010-9563-8