borgbackup/borg

unusual blake2b usage, adopt blake3?

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#8867 opened on May 21, 2025

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 (10 comments) (0 reactions) (1 assignee)Python (10,086 stars) (732 forks)batch import
breakingcmd: transferhelp wantedsecurity

Description

This is from master branch (same in 1.4-maint):

def blake2b_256(key, data):
    return hashlib.blake2b(key+data, digest_size=32).digest()

It is one of the chunkid hashes borg uses.

The usage there is unusual, the python docs rather suggest:

def blake2b_256(key, data):
    return hashlib.blake2b(data, key=key, digest_size=32).digest()

Contributor guide

Tech stack
python
Domain
backend
Issue type
feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
2
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
blocked
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
Python hashlibcryptographic hashing
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
60
Research direction
The issue discusses an unusual usage of hashlib.blake2b in the borg codebase, specifically in the blake2b 256 function that generates chunk IDs. There are two possible paths: correcting the call to use the key parameter properly, or adopting blake3 for potentially better performance. The issue has an assignee, so any contribution should first coordinate with them. The relevant code is likely in borg's hash or crypto module.