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ChiLow and ChiChi: New Constructions for Code Encryption

Authors:
Yanis Belkheyar , Radboud University
Patrick Derbez , Univ Rennes, Inria, CNRS, IRISA
Shibam Ghosh , University Of Haifa
Gregor Leander , Ruhr University Bochum
Silvia Mella , Radboud University
Léo Perrin , Inria
Shahram Rasoolzadeh , Ruhr University Bochum
Lukas Stennes , Ruhr University Bochum
Siwei Sun , School of Cryptology, University of Chinese Academy of Sciences
Gilles Van Assche , STMicroelectronics
Damian Vizár , CSEM
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Conference: EUROCRYPT 2025
Abstract: We study the problem of embedded code encryption, i.e., encryption for binary software code for a secure microcontroller that is stored in an insecure external memory. As every single instruction must be decrypted before it can be executed, this scenario requires an extremely low latency decryption. We present a formal treatment of embedded code encryption security definitions, propose three constructions, namely ACE1, ACE2 and ACE3, and analyze their security. Further, we present ChiLow, a family of tweakable block ciphers and a related PRF specifically designed for embedded code encryption. At the core of ChiLow, there is ChiChi, a new family of non-linear layers of even dimension based on the well-known χ function. Our fully unrolled hardware implementation of ChiLow, using the Nangate 15nm Open Cell Library, achieves a decryption latency of less than 280 picoseconds.
BibTeX
@inproceedings{eurocrypt-2025-35010,
  title={ChiLow and ChiChi: New Constructions for Code Encryption},
  publisher={Springer-Verlag},
  author={Yanis Belkheyar and Patrick Derbez and Shibam Ghosh and Gregor Leander and Silvia Mella and Léo Perrin and Shahram Rasoolzadeh and Lukas Stennes and Siwei Sun and Gilles Van Assche and Damian Vizár},
  year=2025
}