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Strong Physical Unclonable Functions (PUFs), as a promising security primitive, are supposed to be a lightweight alternative to classical cryptography for purposes such as device authentication. Most of the proposed candidates, however, have been plagued by modeling attacks breaking their security claims. The Interpose PUF (iPUF), which has been introduced at CHES 2019, was explicitly designed with state-of-the-art modeling attacks in mind and is supposed to be impossible to break by classical and reliability attacks. In this paper, we analyze its vulnerability to reliability attacks. Despite the increased difficulty, these attacks are still feasible, against the original authors’ claim. We explain how adding constraints to the modeling objective streamlines reliability attacks and allows us to model all individual components of an iPUF successfully. In order to build a practical attack, we give several novel contributions. First, we demonstrate that reliability attacks can be performed not only with covariance matrix adaptation evolution strategy (CMA-ES) but also with gradient-based optimization. Second, we show that the switch to gradient-based reliability attacks makes it possible to combine reliability attacks, weight constraints, and Logistic Regression (LR) into a single optimization objective. This framework makes modeling attacks more efficient, as it exploits knowledge of responses and reliability information at the same time. Third, we show that a differentiable model of the iPUF exists and how it can be utilized in a combined reliability attack. We confirm that iPUFs are harder to break than regular XOR Arbiter PUFs. However, we are still able to break (1,10)-iPUF instances, which were originally assumed to be secure, with less than 107 PUF response queries.

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Symmetric-key cryptography can resist the potential post-quantum attacks expected with the not-so-faraway advent of quantum computing power. Hash-based, code-based, lattice-based, and multivariate-quadratic equations are all other potential candidates, the merit of which is that they are believed to resist both classical and quantum computers, and applying “Shor’s algorithm”—the quantum-computer discrete-logarithm algorithm that breaks classical schemes—to them is infeasible. In this article, we propose, assess, and benchmark reliable constructions for stateless hash-based signatures. Such architectures are believed to be one of the prominent post-quantum schemes, offering security proofs relative to plausible properties of the hash function; however, it is well known that their confidentiality does not guarantee reliable architectures in the presence natural and malicious faults. We propose and benchmark fault diagnosis methods for this post-quantum cryptography variant through case studies for hash functions and present the simulations and implementations results (through application-specific integrated circuit evaluations) to show the applicability of the presented schemes. The proposed approaches make such hash-based constructions more reliable against natural faults and help protecting them against malicious faults and can be tailored based on the resources available and for different reliability objectives.