International Association for Cryptologic Research

International Association
for Cryptologic Research


Efficient Length Doubling From Tweakable Block Ciphers

Yu Long Chen , imec-COSIC, KU Leuven
Atul Luykx , imec-COSIC, KU Leuven, Belgium; Department of Computer Science, University of California, Davis One Shields Ave, Davis, California 95616
Bart Mennink , Digital Security Group, Radboud University, Nijmegen; CWI, Amsterdam
Bart Preneel , imec-COSIC, KU Leuven
DOI: 10.13154/tosc.v2017.i3.253-270
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Abstract: We present a length doubler, LDT, that turns an n-bit tweakable block cipher into an efficient and secure cipher that can encrypt any bit string of length [n..2n − 1]. The LDT mode is simple, uses only two cryptographic primitive calls (while prior work needs at least four), and is a strong length-preserving pseudorandom permutation if the underlying tweakable block ciphers are strong tweakable pseudorandom permutations. We demonstrate that LDT can be used to neatly turn an authenticated encryption scheme for integral data into a mode for arbitrary-length data.
  title={Efficient Length Doubling From Tweakable Block Ciphers},
  journal={IACR Trans. Symmetric Cryptol.},
  publisher={Ruhr-Universität Bochum},
  volume={2017, Issue 3},
  author={Yu Long Chen and Atul Luykx and Bart Mennink and Bart Preneel},