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Sensitive data can be extracted by mounting physical attacks, e.g., photon emission analysis, micro-probing, etc., on integrated circuits (ICs). In this paper, our ultimate goal is to examine provable security approaches that increase the number of simultaneous probes needed to perform probing in order to see how they can complement physical anti-probing countermeasures. Commonly applied mathematical models for probing attacks have employed randomized bits to mask the input, and modified computations. As the number of masks increases, the number of probes needed to extract the secret data increases linearly, assuming noise-free conditions. In another attempt, noisy leakage models have been developed to better mimic real-world scenarios, but their complexity is a major drawback. Hence, extensive research has been performed to show connections between noisy leakage models and probing models. The goal of this survey is to relate the notion of masking with physical backside attack countermeasures, which are limited in practice. To this end, our first milestone is to unify provable probing and side-channel models in order to develop and realize more practical countermeasures. 

Sensitive data contained and processed in integrated circuits (ICs), such as secret keys and encrypted firmware, can be extracted with focused ion beam (FIB) based probing attacks. Due to the unprotected structure on the back-side of the die, the threat of back-side probing attacks is particularly grim. In this study, we develop a quantitative model for back-side probing attacks and apply it to three latest technology nodes 7, 10 and 14 nm with 3, 5, 8 and 10 FIB aspect ratios. The probed opening is modeled to have shape of conical frustum, which allows FIB beam diameter, in range of 10nm to 33.3nm, to produce the opening with diameter in range of 22nm to 57.3nm. We also propose a novel back-side shield design structure with an estimated 16% area overhead that terminates the die operations as a result of probing to prevent malicious data extraction. Proposed back-side countermeasure increases the complexity of the attack performed on protected die.