2023 journal article
SeqL plus : Secure Scan-Obfuscation With Theoretical and Empirical Validation
IEEE TRANSACTIONS ON COMPUTER-AIDED DESIGN OF INTEGRATED CIRCUITS AND SYSTEMS, 42(5), 1406–1410.
author keywords: Flip-flops; Logic gates; Security; Complexity theory; Resists; Resilience; Iterative algorithms; IP piracy; scan-chains; scan-scrambling
TL;DR:
This study reveals the first formulation and complexity analysis of Boolean satisfiability (SAT)-based attack on scan-scrambling and proposes an iterative swapping-based scan-cell scrambling algorithm to defeat SAT-based attack.
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Source: Web Of Science
Added: June 5, 2023
Scan-obfuscation is a powerful methodology to protect Silicon-based intellectual property from theft. Prior work on scan-obfuscation in the context of logic-locking have unique limitations, which are addressed by our previous work, SeqL, which looks at functional output corruption to obfuscate scan-chains, but is unable to resist removal attacks on circuits with inadequate number of flip-flops without feedback. To address this issue, we propose to scramble flip-flops with feedback to increase key length without introducing further vulnerabilities. This study reveals the first formulation and complexity analysis of Boolean satisfiability (SAT)-based attack on scan-scrambling. We formulate the attack as a conjunctive normal form (CNF) using a worst-case <inline-formula> <tex-math notation="LaTeX">$\mathcal {O}(n^{3})$ </tex-math></inline-formula> reduction in terms of scramble-graph size <inline-formula> <tex-math notation="LaTeX">$n$ </tex-math></inline-formula>. In order to defeat SAT-based attack, we propose an iterative swapping-based scan-cell scrambling algorithm that has <inline-formula> <tex-math notation="LaTeX">$\mathcal {O}(n)$ </tex-math></inline-formula> implementation time-complexity and <inline-formula> <tex-math notation="LaTeX">$\mathcal {O}(2^{\lfloor ({\alpha.n+1}/{3}) \rfloor })$ </tex-math></inline-formula> SAT-decryption time-complexity in terms of a user-configurable cost constraint <inline-formula> <tex-math notation="LaTeX">$\alpha ~(0 < \alpha \le 1)$ </tex-math></inline-formula>.