  We propose a secure and lightweight key based challenge obfuscation for
strong PUFs. Our architecture is designed to be resilient against learning
attacks. Our obfuscation mechanism uses non-linear feedback shift registers
(NLFSRs). Responses are directly provided to the user, without error correction
or extra post-processing steps. We also discuss the cost of protecting our
architecture against power analysis attacks with clock randomization, and
Boolean masking. Security against learning attacks is assessed using avalanche
criterion, and deep-neural network attacks. We designed a testchip in 65 nm
CMOS. When compared to the baseline arbiter PUF implementation, the cost
increase of our proposed architecture is 1.27x, and 2.2x when using clock
randomization, and Boolean masking, respectively.
