SCRAMBLE-CFI: Mitigating Fault-Induced Control-Flow Attacks on OpenTitan

Pascal Nasahl, Stefan Mangard

Research output: Chapter in Book/Report/Conference proceedingConference paperpeer-review


Secure elements physically exposed to adversaries are frequently targeted by fault attacks. These attacks can be utilized to hijack the control-flow of software allowing the attacker to bypass security measures, extract sensitive data, or gain full code execution.
In this paper, we systematically analyze the threat vector of fault-induced control-flow manipulations on the open-source OpenTitan secure element. Our thorough analysis reveals that current countermeasures of this chip either induce large area overheads or still cannot prevent the attacker from exploiting the identified threats.
In this context, we introduce SCRAMBLE-CFI, an encryption-based control-flow integrity scheme utilizing existing hardware features of OpenTitan. SCRAMBLE-CFI confines, with minimal hardware overhead, the impact of fault-induced control-flow attacks by encrypting each function with a different encryption tweak at load-time. At runtime, code only can be successfully decrypted when the correct decryption tweak is active. We open-source our hardware changes and release our LLVM toolchain automatically protecting programs. Our analysis shows that SCRAMBLE-CFI complementarily enhances security guarantees of OpenTitan with a negligible hardware overhead of less than 3.97 % and a runtime overhead of 7.02 % for the Embench-IoT benchmarks.
Original languageEnglish
Title of host publicationGLSVLSI 2023 - Proceedings of the Great Lakes Symposium on VLSI 2023
Pages45 - 50
Number of pages6
ISBN (Electronic)9798400701252
Publication statusPublished - 5 Jun 2023
Event2023 ACM Great Lakes Symposium on VLSI: GLSVLSI 2023 - Knoxville, United States
Duration: 5 Jun 20237 Jun 2023

Publication series

NameProceedings of the ACM Great Lakes Symposium on VLSI, GLSVLSI


Conference2023 ACM Great Lakes Symposium on VLSI
Abbreviated titleGLSVLSI 2023
Country/TerritoryUnited States


  • cryptographic control-flow integrity
  • fault attacks
  • secure element

ASJC Scopus subject areas

  • General Engineering


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