Paper 2024/745

FRAST: TFHE-friendly Cipher Based on Random S-boxes

Mingyu Cho, Mobilint, Inc.
Woohyuk Chung, Korea Advanced Institute of Science and Technology
Jincheol Ha, Korea Advanced Institute of Science and Technology
Jooyoung Lee, Korea Advanced Institute of Science and Technology
Eun-Gyeol Oh, Korea Advanced Institute of Science and Technology
Mincheol Son, Korea Advanced Institute of Science and Technology
Abstract

A transciphering framework, also known as hybrid homomorphic encryption, is a practical method of combining a homomorphic encryption~(HE) scheme with a symmetric cipher in the client-server model to reduce computational and communication overload on the client side. As a server homomorphically evaluates a symmetric cipher in this framework, new design rationales are required for ``HE-friendly'' ciphers that take into account the specific properties of the HE schemes. In this paper, we propose a new TFHE-friendly cipher, dubbed $\mathsf{FRAST}$, with a TFHE-friendly round function based on a random S-box to minimize the number of rounds. The round function of $\mathsf{FRAST}$ can be efficiently evaluated in TFHE by a new optimization technique, dubbed double blind rotation. Combined with our new WoP-PBS method, the double blind rotation allows computing multiple S-box calls in the round function of $\mathsf{FRAST}$ at the cost of a single S-box call. In this way, $\mathsf{FRAST}$ enjoys $2.768$ (resp. $10.57$) times higher throughput compared to $\mathsf{Kreyvium}$ (resp. $\mathsf{Elisabeth}$) for TFHE keystream evaluation in the offline phase of the transciphering framework at the cost of slightly larger communication overload.

Metadata
Available format(s)
PDF
Category
Secret-key cryptography
Publication info
Published by the IACR in TOSC 2024
Keywords
homomorphic encryptionprogrammable bootstrappingtransciphering frameworkstream cipherHE-friendly cipher
Contact author(s)
mingyu @ mobilint com
hephaistus @ kaist ac kr
smilecjf @ kaist ac kr
hicalf @ kaist ac kr
eun-gyeol oh @ kaist ac kr
encrypted def @ kaist ac kr
History
2024-09-19: revised
2024-05-16: received
See all versions
Short URL
https://ia.cr/2024/745
License
Creative Commons Attribution
CC BY

BibTeX

@misc{cryptoeprint:2024/745,
      author = {Mingyu Cho and Woohyuk Chung and Jincheol Ha and Jooyoung Lee and Eun-Gyeol Oh and Mincheol Son},
      title = {{FRAST}: {TFHE}-friendly Cipher Based on Random S-boxes},
      howpublished = {Cryptology {ePrint} Archive, Paper 2024/745},
      year = {2024},
      url = {https://eprint.iacr.org/2024/745}
}
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