Format-preserving encryption (FPE) enables encryption while maintaining syntactic properties such as character sets. The current NIST standard FF1 uses multi-round Feistel networks that sacrifice performance for flexibility, while FF3-1 was withdrawn in 2025 following successful cryptanalytic attacks. FAST, proposed as a faster alternative, has not been widely implemented due to its complexity, leaving limited practical alternatives. We present HCTR2-FP and HCTR3-FP, format-preserving adaptations of the HCTR2 and HCTR3 wide-block tweakable ciphers. These variants preserve the single-pass Hash-Encrypt-Hash structure while operating on arbitrary radix domains through base-radix encoding and modular arithmetic. The constructions are simple to implement and analyze, and benchmarks demonstrate significant speedup over FF1.
Note: Added references to the Vistrutah and the Samvadini-AEAD papers.
BibTeX
@misc{cryptoeprint:2025/1888,
author = {Frank Denis},
title = {{HCTR2}-{FP} and {HCTR3}-{FP}: Format-Preserving Encryption from Wide-Block Ciphers},
howpublished = {Cryptology {ePrint} Archive, Paper 2025/1888},
year = {2025},
url = {https://eprint.iacr.org/2025/1888}
}
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