Paper 2021/425

Related-Key Analysis of Generalized Feistel Networks with Expanding Round Functions

Yuqing Zhao, Wenqi Yu, and Chun Guo

Abstract

We extend the prior provable related-key security analysis of (generalized) Feistel networks (Barbosa and Farshim, FSE 2014; Yu et al., Inscrypt 2020) to the setting of expanding round functions, i.e., n-bit to m-bit round functions with n < m. This includes Expanding Feistel Networks (EFNs) that purely rely on such expanding round functions, and Alternating Feistel Networks (AFNs) that alternate expanding and contracting round functions. We show that, when two independent keys $K_1,K_2$ are alternatively used in each round, (a) $2\lceil\frac{m}{n}\rceil+2$ rounds are sufficient for related-key security of EFNs, and (b) a constant number of 4 rounds are sufficient for related-key security of AFNs. Our results complete the picture of provable related-key security of GFNs, and provide additional theoretical support for the AFN-based NIST format preserving encryption standards FF1 and FF3.

Metadata
Available format(s)
PDF
Category
Secret-key cryptography
Publication info
Preprint. MINOR revision.
Contact author(s)
yqZhao1997 @ 163 com
History
2021-04-06: received
Short URL
https://ia.cr/2021/425
License
Creative Commons Attribution
CC BY

BibTeX

@misc{cryptoeprint:2021/425,
      author = {Yuqing Zhao and Wenqi Yu and Chun Guo},
      title = {Related-Key Analysis of Generalized Feistel Networks with Expanding Round Functions},
      howpublished = {Cryptology ePrint Archive, Paper 2021/425},
      year = {2021},
      note = {\url{https://eprint.iacr.org/2021/425}},
      url = {https://eprint.iacr.org/2021/425}
}
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