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Pre-silicon tools for hardening hardware against side-channel and fault injection attacks have become popular recently. However, the security of the system is still threatened by sophisticated physical attacks, which exploit the physical layer characteristics of the computing system beyond the integrated circuits (ICs) and, therefore, bypass the conventional countermeasures. Further, environmental conditions for the hardware can also impact side-channel leakage and fault vulnerability in unexpected ways that are challenging to model in pre-silicon. Thus, attacks cannot be addressed solely by conventional countermeasures at higher layers of the compute stack due to the lack of awareness about the events occurring at the physical layer during runtime. In this paper, we first discuss why the current pre-silicon security and verification tools might fail to achieve security against physical threats in the post-silicon phase. Afterward, we provide insights from the fields of power/signal integrity (PI/SI), and failure analysis (FA) to understand the fundamental issue with the failed current practices. We argue that hardware-based moving target defenses (MTDs) to randomize the physical fabric’s characteristics of the system can mitigate such unaccounted post-silicon threats. We show the effectiveness of such an approach by presenting the results of two case studies in which we perform powerful attacks, such as impedance analysis and laser voltage probing. Finally, we review the overhead of our proposed approach and show that the imposed overhead by MTD solutions can be addressed by making them active only when a threat is detected. 

The threats of physical side-channel attacks and their countermeasures have been widely researched. Most physical side-channel attacks rely on the unavoidable influence of computation or storage on current consumption or voltage drop on a chip. Such data-dependent influence can be exploited by, for instance, power or electromagnetic analysis. In this work, we introduce a novel non-invasive physical side-channel attack, which exploits the data-dependent changes in the impedance of the chip. Our attack relies on the fact that the temporarily stored contents in registers alter the physical characteristics of the circuit, which results in changes in the die's impedance. To sense such impedance variations, we deploy a well-known RF/microwave method called scattering parameter analysis, in which we inject sine wave signals with high frequencies into the system's power distribution network (PDN) and measure the echo of the signals. We demonstrate that according to the content bits and physical location of a register, the reflected signal is modulated differently at various frequency points enabling the simultaneous and independent probing of individual registers. Such side-channel leakage challenges the t-probing security model assumption used in masking, which is a prominent side-channel countermeasure. To validate our claims, we mount non-profiled and profiled impedance analysis attacks on hardware implementations of unprotected and high-order masked AES. We show that in the case of the profiled attack, only a single trace is required to recover the secret key. Finally, we discuss how a specific class of hiding countermeasures might be effective against impedance leakage. 

Contactless probing methods through the chip backside have been demonstrated to be powerful attack techniques in the field of electronic security. However, these attacks typically require the adversary to run the circuit under specific conditions, such as enforcing the switching of gates or registers with certain frequencies or repeating measurements over multiple executions to achieve an acceptable signal-to-noise ratio (SNR). Fulfilling such requirements may not always be feasible due to challenges such as low-frequency switching or inaccessibility of the control signals. In this work, we assess these requirements for contactless electron- and photon-based probing attacks by performing extensive experiments. Our findings demonstrate that E-beam probing, in particular, has the potential to outperform optical methods in scenarios involving static or low-frequency circuit activities.