Paper 2023/085 Original: eprint.iacr.org/2023/085 ↗
The Security of ChaCha20-Poly1305 in the Multi-user Setting
Abstract
The ChaCha20-Poly1305 AEAD scheme is being increasingly widely deployed in practice. Practitioners need proven security bounds in order to set data limits and rekeying intervals for the scheme. But the formal security analysis of ChaCha20-Poly1305 currently lags behind that of AES-GCM. The only extant analysis (Procter, 2014) contains a flaw and is only for the single-user setting. We rectify this situation. We prove a multi-user security bound on the AEAD security of ChaCha20-Poly1305 and establish the tightness of each term in our bound through matching attacks. We show how our bound differs both qualitatively and quantitatively from the known bounds for AES-GCM, highlighting how subtle design choices lead to distinctive security properties. We translate our bound to the nonce-randomized setting employed in TLS 1.3 and elsewhere, and we additionally improve the corresponding security bounds for GCM. Finally, we provide a simple yet stronger variant of ChaCha20-Poly1305 that addresses the deficiencies highlighted by our analysis.
Metadata
- Available format(s)
PDF- Category
- Secret-key cryptography
- Publication info
- Preprint.
- History
- 2023-01-24: last updated
- 2023-01-24: published
- Short URL
- https://ia.cr/2023/085
- License
- https://creativecommons.org/licenses/by/4.0/
BibTeX
@misc{cryptoeprint:2023/085,
author = {Jean Paul Degabriele and Jérôme Govinden and Felix Günther and Kenneth G. Paterson},
title = {The Security of ChaCha20-Poly1305 in the Multi-user Setting},
howpublished = {Cryptology {ePrint} Archive, Paper 2023/085},
year = {2023},
url = {https://eprint.iacr.org/2023/085}
}