Paper 2019/060

CycSAT-Unresolvable Cyclic Logic Encryption Using Unreachable States

Amin Rezaei, You Li, Yuanqi Shen, Shuyu Kong, and Hai Zhou


Logic encryption has attracted much attention due to increasing IC design costs and growing number of untrusted foundries. Unreachable states in a design provide a space of flexibility for logic encryption to explore. However, due to the available access of scan chain, traditional combinational encryption cannot leverage the benefit of such flexibility. Cyclic logic encryption inserts key-controlled feedbacks into the original circuit to prevent piracy and overproduction. Based on our discovery, cyclic logic encryption can utilize unreachable states to improve security. Even though cyclic encryption is vulnerable to a powerful attack called CycSAT, we develop a new way of cyclic encryption by utilizing unreachable states to defeat CycSAT. The attack complexity of the proposed scheme is discussed and its robustness is demonstrated.

Available format(s)
Publication info
Published elsewhere. Minor revision. Asia South Pacific Design Automation Conference
logic encryptionSAT-based attackcyclic circuitstate machine
Contact author(s)
haizhou @ northwestern edu
2019-01-25: received
Short URL
Creative Commons Attribution


      author = {Amin Rezaei and You Li and Yuanqi Shen and Shuyu Kong and Hai Zhou},
      title = {CycSAT-Unresolvable Cyclic Logic Encryption Using Unreachable States},
      howpublished = {Cryptology ePrint Archive, Paper 2019/060},
      year = {2019},
      note = {\url{}},
      url = {}
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