TheArchive/restic
1
0
Fork 0
mirror of https://github.com/restic/restic.git synced 2025-08-23 17:55:17 +00:00
Code Issues Packages Projects Releases Wiki Activity

add changelog and update threat model

Browse Source
This commit is contained in:
Michael Eischer
2025-03-22 22:20:36 +01:00
parent 8d2d50d095
commit 37aa4f824f
2 changed files with 33 additions and 0 deletions
Download Patch File Download Diff File Expand all files Collapse all files

23
changelog/unreleased/issue-5291 Normal file
View File

@@ -0,0 +1,23 @@
Security: Mitigate attack on content-defined chunking algorithm
Restic uses [Rabin Fingerprints](https://restic.net/blog/2015-09-12/restic-foundation1-cdc/)
for its content-defined chunker. The algorithm relies on a secret polynomial
to split files into chunks.
As shown in the paper "[Chunking Attacks on File Backup Services using Content-Defined Chunking](https://eprint.iacr.org/2025/532.pdf)"
by Boris Alexeev, Colin Percival and Yan X Zhang, an
attacker that can observe chunk sizes for a known file can derive the secret
polynomial. Knowledge of the polynomial might in some cases allow an attacker
to check whether certain large files are stored in a repository.
A practical attack is nevertheless hard as restic merges multiple chunks into
opaque pack files and by default processes multiple files in parallel. This
likely prevents an attacker from matching pack files to the attacker-known file
and thereby prevents the attack.
We have added a mitigation to restic, which randomizes how chunks are assembled
into pack files. This prevents an attacker from guessing which chunks are part
of a pack file and thereby prevents learning the chunk sizes.
https://github.com/restic/restic/issues/5291
https://github.com/restic/restic/pull/5295