### Tweakable HCTR: A BBB Secure Tweakable Enciphering Scheme

Avijit Dutta and Mridul Nandi

##### Abstract

\textsf{HCTR}, proposed by Wang et al., is one of the most efficient candidates of tweakable enciphering schemes that turns an $n$-bit block cipher into a variable input length tweakable block cipher. Wang et al. have shown that \textsf{HCTR} offers a cubic security bound against all adaptive chosen plaintext and chosen ciphertext adversaries. Later in FSE 2008, Chakraborty and Nandi have improved its bound to $O(\sigma^2 / 2^n)$, where $\sigma$ is the total number of blocks queried and $n$ is the block size of the block cipher. In this paper, we propose \textbf{tweakable \textsf{HCTR}} that turns an $n$-bit tweakable block cipher to a variable input length tweakable block cipher by replacing all the block cipher calls of \textsf{HCTR} with tweakable block cipher. We show that when there is no repetition of the tweak, tweakable \textsf{HCTR} enjoys the optimal security against all adaptive chosen plaintext and chosen ciphertext adversaries. However, if the repetition of the tweak is limited, then the security of the construction remains close to the security bound in no repetition of the tweak case. Hence, it gives a graceful security degradation with the maximum number of repetition of tweaks.

Available format(s)
Category
Secret-key cryptography
Publication info
Published elsewhere. Indorcypt, 2018
DOI
10.1007/978-3-030-05378-9
Keywords
Tweakable Enciphering SchemeHCTRTSPRPH-Coefficient.
Contact author(s)
avirocks dutta13 @ gmail com
History
Short URL
https://ia.cr/2019/1324

CC BY

BibTeX

@misc{cryptoeprint:2019/1324,
author = {Avijit Dutta and Mridul Nandi},
title = {Tweakable HCTR: A BBB Secure Tweakable Enciphering Scheme},
howpublished = {Cryptology ePrint Archive, Paper 2019/1324},
year = {2019},
doi = {10.1007/978-3-030-05378-9},
note = {\url{https://eprint.iacr.org/2019/1324}},
url = {https://eprint.iacr.org/2019/1324}
}

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