Physical Unclonable Functions (PUFs) provide means to generate chip individual keys, especially for low-cost applications such as the Internet of Things (IoT). They are intrinsically robust against reverse engineering, and more cost-effective than non-volatile memory (NVM). For several PUF primitives, countermeasures have been proposed to mitigate side-channel weaknesses. However, most mitigation techniques require substantial design effort and/or complexity overhead, which cannot be tolerated in low-cost IoT scenarios. In this paper, we first analyze side-channel vulnerabilities of the Loop PUF, an area efficient PUF implementation with a configurable delay path based on a single ring oscillator (RO). We provide side-channel analysis (SCA) results from power and electromagnetic measurements. We confirm that oscillation frequencies are easily observable and distinguishable, breaking the security of unprotected Loop PUF implementations. Second, we present a low-cost countermeasure based on temporal masking to thwart SCA that requires only one bit of randomness per PUF response bit. The randomness is extracted from the PUF itself creating a self-secured PUF. The concept is highly effective regarding security, low complexity, and low design constraints making it ideal for applications like IoT. Finally, we discuss trade-offs of side-channel resistance, reliability, and latency as well as the transfer of the countermeasure to other RO-based PUFs.
Physical Unclonable Functions (PUFs) derive unique secrets from internal manufacturing variations in integrated circuits. This work shows that key generation with PUFs is a practical application of the generic information theoretic problem of secret key agreement with a compound source.We present an improved secure sketch construction with our new optimal syndrome coding scheme for PUFs, Systematic Low Leakage Coding (SLLC). Our scheme provides inherent information theoretic security without the need of a hash function or strong extractor, and optimal asymptotic performance concerning maximum key size and minimum helper data size. The secrecy leakage is bounded by a small epsilon that goes to zero for sufficiently good PUFs.The reference implementation for an ASIC application scenario shows that our scheme does not require the 47% hardware overhead for the hash function that is mandatory for the state-of-the-art approaches.
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