Physical Unclonable Functions (PUFs) are circuits designed to extract physical randomness from the underlying circuit. This randomness depends on the manufacturing process. It differs for each device enabling chip-level authentication and key generation [1] applications. We present a protocol utilizing a PUF for secure data transmission. Parties each have a PUF used for encryption and decryption; this is facilitated by constraining the PUF to be commutative. This framework is evaluated with a primitive permutation network -a barrel shifter [2]. Physical randomness is derived from the delay of different shift paths. Barrel shifter (BS) PUF captures the delay of different shift paths. This delay is entangled with message bits before they are sent across an insecure channel. BS-PUF is implemented using transmission gates; their characteristics ensure same-chip reproducibility, a necessary property of PUFs. Post-layout simulations of a common centroid layout [3] 8-level barrel shifter in 0.13 µm technology assess uniqueness, stability and randomness properties. BS-PUFs pass all selected NIST statistical randomness tests [4]. Stability similar to Ring Oscillator (RO) PUFs under environment variation is shown. Logistic regression of 100, 000 plaintext-ciphertext pairs (PCPs) failed to successfully model BS-PUF behavior.The key contributions of this paper are: (1) We explore several PUFs based information exchange protocols which serves to encrypt/decrypt information, find the best protocol through analysis; (2) this protocol requires PUFs to be physically commutative. We develop a framework for physically commutative PUFs based on permutation networks; (3) We evaluate permutation networks based physically commutative PUF framework with a primitive permutation network using barrel shifters. Barrel shifters have symmetric input to output path delays. Hence if two different paths within the same barrel shifter generate randomly uncorrelated delays, it is a strong lower bound for randomness in general permutation networks with more skewed path delays; (4) The results show good same chip, same path delay reproducibility; good differentiation between different chip, same path delay and same chip, different path delay; delays within 1-bit accuracy for the logic high and logic low propagation through the same path demonstrates physical commutativity; and good pseudorandom number generator properties for delay. This paper is organized as follows. Section II introduces communication protocol. Section III illustrates commutative PUF encryption protocol. Section IV shows the schematic of barrel shifter PUF. Section V presents the detailed circuit implementation of barrel shifter PUF. Variability/reproducibility and commutativity test results based on post-layout simulations are presented in Section VI. Performance of BS-PUFs based encryption protocol is evaluated in Section VII. Sections VIII and IX discuss future work and conclusions. II. COMMUNICATION PROTOCOL

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In this paper, a novel voice-based User-Device (UD-) physical unclonable function (PUF) is demonstrated. In traditional PUFs, variability of challenge-response pairs (CRPs) only comes from physical randomness of silicon. Recently, a new type of PUF, touch screen-based UD-PUF was proposed, which entangles human user biometric variability with the silicon variability. Any silicon-based mobile device sensor which is a UI element can potentially seed such a UD-PUF. Having multiple orthogonal sensor space UD-PUFs helps robustness. If one UD-PUF behaves poorly in certain environmental conditions, another one might behave well. In voice UD-PUF, challenges are single words chosen by the user. The user speaks the challenge word into the microphone of the mobile device. The speech has natural human biometric variability. Raw microphone output data of analog to digital converter (ADC) also reflects the silicon variability. This voice microphone data sequence can be quantized into a binary sequence leading to a PUFa physical randomness derived, unclonable function. To ensure reproducibility, a background noise reduction algorithm, a statistical error correction, and a frequency domain canonical representation are utilized. Both variability and reproducibility of this voice UD-PUF are evaluated. Several authentication algorithms are proposed in this paper. Pixel-matching authentication algorithm provides an average 15.33% false positive rate and an average 12.30% false negative rate while frame-count authentication algorithm provides an average 6.27% false positive rate and an average 13.23% false negative rate. For variability, we show 250+ bits Hamming distance, on average, between 512 bits binary responses of different (user, device, challenge) combinations. We also assess the pseudorandom number generation properties of voice UD-PUF by putting its binary responses through UMontreal TESTU01 suite of tests. The best voice UD-PUF algorithm passed all 26 randomness tests.

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