### Towards Tight Security of Cascaded LRW2

Bart Mennink

##### Abstract

The Cascaded LRW2 tweakable block cipher was introduced by Landecker et al. at CRYPTO 2012, and proven secure up to $2^{2n/3}$ queries. There has not been any attack on the construction faster than the generic attack in $2^n$ queries. In this work we initiate the quest towards a tight bound. We first present a distinguishing attack in $2n^{1/2}2^{3n/4}$ queries against a generalized version of the scheme. The attack is supported with an experimental verification and a formal success probability analysis. We subsequently discuss non-trivial bottlenecks in proving tight security, most importantly the distinguisher's freedom in choosing the tweak values. Finally, we prove that if every tweak value occurs at most $2^{n/4}$ times, Cascaded LRW2 is secure up to $2^{3n/4}$ queries.

Available format(s)
Category
Secret-key cryptography
Publication info
A minor revision of an IACR publication in TCC 2018
Keywords
Contact author(s)
b mennink @ cs ru nl
History
2018-09-12: revised
See all versions
Short URL
https://ia.cr/2018/434

CC BY

BibTeX

@misc{cryptoeprint:2018/434,
author = {Bart Mennink},
title = {Towards Tight Security of Cascaded LRW2},
howpublished = {Cryptology ePrint Archive, Paper 2018/434},
year = {2018},
note = {\url{https://eprint.iacr.org/2018/434}},
url = {https://eprint.iacr.org/2018/434}
}

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