Chunking Attacks on File Backup Services using Content-Deﬁned Chunking

Boris Alexeev; Colin Percival; Yan X Zhang

Paper 2025/532

Chunking Attacks on File Backup Services using Content-Deﬁned Chunking

Boris Alexeev

Colin Percival, Tarsnap Backup Inc.

Yan X Zhang, San Jose State University

Abstract

Systems such as file backup services often use content-defined chunking (CDC) algorithms, especially those based on rolling hash techniques, to split files into chunks in a way that allows for data deduplication. These chunking algorithms often depend on per-user parameters in an attempt to avoid leaking information about the data being stored. We present attacks to extract these chunking parameters and discuss protocol-agnostic attacks and loss of security once the parameters are breached (including when these parameters are not setup at all, which is often available as an option). Our parameter-extraction attacks themselves are protocol-specific but their ideas are generalizable to many potential CDC schemes.

Note: Typo fixes.

Metadata

Available format(s): PDF
Category: Attacks and cryptanalysis
Publication info: Preprint.
Keywords: Content-defined chunking CDC Rolling hash Backup
Contact author(s): cperciva @ tarsnap com
History: 2025-03-24: revised; 2025-03-21: received; See all versions
Short URL: https://ia.cr/2025/532
License: CC BY

BibTeX

@misc{cryptoeprint:2025/532,
      author = {Boris Alexeev and Colin Percival and Yan X Zhang},
      title = {Chunking Attacks on File Backup Services using Content-Deﬁned Chunking},
      howpublished = {Cryptology {ePrint} Archive, Paper 2025/532},
      year = {2025},
      url = {https://eprint.iacr.org/2025/532}
}