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Evaluating the Indistinguishability of Logic Locking using K-Cut Enumeration and Boolean Matching

Jonathan Cruz, Jason Hamlet

TL;DR

This work highlights recent efforts that can be used to analyze the indistinguishability of logic locking techniques, and proposes a new method of evaluation based on comparing distributions of $k$-cuts, which is akin to comparing against a library of sub-functions.

Abstract

Logic locking as a solution for semiconductor intellectual property (IP) confidentiality has received considerable attention in academia, but has yet to produce a viable solution to protect against known threats. In part due to a lack of rigor, logic locking defenses have been historically short-lived, which is an unacceptable risk for hardware-based security solutions for critical systems that may be fielded for decades. Researchers have worked to map the concept of cryptographic indistinguishability to logic locking, as indistinguishability provides strong security guarantees. In an effort to bridge theory and practice, we highlight recent efforts that can be used to analyze the indistinguishability of logic locking techniques, and propose a new method of evaluation based on comparing distributions of $k$-cuts, which is akin to comparing against a library of sub-functions. We evaluate our approach on several different classes of logic locking and show up to 92% average accuracy in correctly identifying which design was locked, even in the presence of resynthesis, suggesting that the evaluated locks do not provide indistinguishability.

Evaluating the Indistinguishability of Logic Locking using K-Cut Enumeration and Boolean Matching

TL;DR

This work highlights recent efforts that can be used to analyze the indistinguishability of logic locking techniques, and proposes a new method of evaluation based on comparing distributions of -cuts, which is akin to comparing against a library of sub-functions.

Abstract

Logic locking as a solution for semiconductor intellectual property (IP) confidentiality has received considerable attention in academia, but has yet to produce a viable solution to protect against known threats. In part due to a lack of rigor, logic locking defenses have been historically short-lived, which is an unacceptable risk for hardware-based security solutions for critical systems that may be fielded for decades. Researchers have worked to map the concept of cryptographic indistinguishability to logic locking, as indistinguishability provides strong security guarantees. In an effort to bridge theory and practice, we highlight recent efforts that can be used to analyze the indistinguishability of logic locking techniques, and propose a new method of evaluation based on comparing distributions of -cuts, which is akin to comparing against a library of sub-functions. We evaluate our approach on several different classes of logic locking and show up to 92% average accuracy in correctly identifying which design was locked, even in the presence of resynthesis, suggesting that the evaluated locks do not provide indistinguishability.
Paper Structure (15 sections, 6 figures, 3 tables)

This paper contains 15 sections, 6 figures, 3 tables.

Table of Contents

  1. Introduction
  2. Background
  3. Logic Locking
  4. Indistinguishability
  5. Related Works
  6. Threat Model
  7. Indistinguishability under Chosen Design Plaintext Attack
  8. Preliminaries
  9. Design Pre-processing and Data Labeling
  10. Cut Enumeration
  11. Evaluation
  12. Experimental Setup
  13. Results
  14. Discussion & Limitations
  15. Conclusion

Figures (6)

  • Figure 1: Example highlighting key gate (red) placement and potential structural and functional transformations from locking. (a) The original c17 benchmark with 3-cut distribution ((G5,G3), (G5,G2), (G5,G3,G2), (G3,G1), (G2,G1), (G4,G2), (G4,G0)). (b) c17 locked with TRLL which transforms the original design by replacing inverters with XOR key gates with key value 1. The 3-cut distribution excluding key gates is ((G5,G3), (G5,G2), (G5,G3,G2), (G4,G2)).
  • Figure 2: Overall flow for $K$-Cut Enumeration Chosen Design Plaintext Analysis.
  • Figure 3: NPN similarity of 4-cut distributions between locked and reference designs. The top 20 cuts were taken for each gate. Top row: 64-bit keys, bottom row 128-bit keys.
  • Figure 4: NPN similarity of 6-cut distributions between locked and reference designs. The top 20 cuts were taken for each gate. Top row: 64-bit keys, bottom row 128-bit keys.
  • Figure 5: NPN similarity of 8-cut distributions between locked and reference designs. The top 20 cuts were taken for each gate. Top row: 64-bit keys, bottom row 128-bit keys.
  • ...and 1 more figures