implementing-immutable-backup-with-restic

name	implementing-immutable-backup-with-restic
description	Implements immutable backup strategy using restic with S3-compatible storage and object lock for ransomware-resistant data protection. Automates backup creation, integrity verification via restic check --read-data, snapshot retention policy enforcement, and restore testing. Integrates with AWS S3 Object Lock, MinIO, and Backblaze B2 for WORM (Write Once Read Many) storage that prevents backup deletion or encryption by ransomware actors.
domain	cybersecurity
subdomain	ransomware-defense
tags	["restic","backup","immutable","ransomware","s3","object-lock","worm","recovery"]
version	1.0.0
author	mahipal
license	Apache-2.0
nist_ai_rmf	["MEASURE-2.7","MAP-5.1","MANAGE-2.4"]
atlas_techniques	["AML.T0070","AML.T0066","AML.T0082"]
nist_csf	["PR.DS-11","RS.MA-01","RC.RP-01","PR.IR-01"]

Implementing Immutable Backup with Restic

When to Use

• Establishing ransomware-resistant backup infrastructure with cryptographic integrity verification
• Implementing 3-2-1-1-0 backup strategy where the extra 1 is an immutable copy
• Automating backup verification workflows that test restore capability on a schedule
• Protecting backup repositories from deletion or modification by compromised admin accounts
• Meeting compliance requirements for data retention with tamper-proof storage

Do not use as the sole backup solution without also maintaining offline/air-gapped copies. Object lock protects against logical deletion but not physical storage failure.

Common Misconfigurations & Verification

• Repo not actually immutable — Governance instead of Compliance: S3 Object Lock in GOVERNANCE mode lets any principal with s3:BypassGovernanceRetention delete objects, so a compromised admin key wipes backups. Use COMPLIANCE mode where even root cannot delete before retention expires. Verify with aws s3api get-object-lock-configuration.
• restic forget --prune defeats immutability: prune rewrites/deletes pack files; if Object Lock retention is shorter than your --keep window, prune fails or, worse, the lock window expires and an attacker prunes everything. Keep retention ≥ longest snapshot policy AND longer than typical ransomware dwell time (~21 days, prefer 30-90).
• Repo password / credentials stored on the backed-up host: if RESTIC_PASSWORD and the S3 keys live on the same server ransomware encrypts, the attacker gets repo write access. Store the password in a separate secrets manager and use append-only/write-only IAM keys for the backup client so it can add but not delete snapshots.
• check without --read-data: plain restic check only validates structure, not blob contents. Schedule restic check --read-data (or --read-data-subset) so bit-rot and tampering are actually caught — that's the "0 errors" in 3-2-1-1-0.
• Verification: run a real restore of random files to a temp path and diff checksums against source; attempt a delete of a locked object and confirm it's denied; confirm a snapshot taken today cannot be removed before the retention date.

Prerequisites

• restic binary installed (https://restic.readthedocs.io/)