Paper 2020/1049
Rotational analysis of ChaCha permutation
Stefano Barbero, Emanuele Bellini, and Rusydi Makarim
Abstract
We show that the underlying permutation of ChaCha20 stream cipher does not behave as a random permutation for up to 17 rounds with respect to rotational cryptanalysis. In particular, we derive a lower and an upper bound for the rotational probability through ChaCha quarter round, we show how to extend the bound to a full round and then to the full permutation. The obtained bounds show that the probability to find what we call a parallel rotational collision is, for example, less than $2^{-488}$ for 17 rounds of ChaCha permutation, while for a random permutation of the same input size, this probability is $2^{-511}$. We remark that our distinguisher is not an attack to ChaCha20 stream cipher, but rather a theoretical analysis of its internal permutation from the point of view of rotational cryptanalysis.
Metadata
- Available format(s)
-
PDF
- Category
- Secret-key cryptography
- Publication info
- Preprint. MINOR revision.
- Keywords
- ChaCha20Stream CipherRotational cryptanalysisPermutationDistinguisher
- Contact author(s)
- eemanuele bellini @ gmail com
- History
- 2020-09-01: received
- Short URL
- https://ia.cr/2020/1049
- License
-
CC BY
BibTeX
@misc{cryptoeprint:2020/1049,
author = {Stefano Barbero and Emanuele Bellini and Rusydi Makarim},
title = {Rotational analysis of {ChaCha} permutation},
howpublished = {Cryptology {ePrint} Archive, Paper 2020/1049},
year = {2020},
url = {https://eprint.iacr.org/2020/1049}
}
