Signed Commits and Git Security¶
Overview¶
Configure commit signing (SSH preferred for simplicity), verify signatures, and apply Git/GitHub security baselines: branch protection, secret hygiene, and least-privilege access.
Author email in Git is forgeable. Signed commits prove the committer held a key tied to a verified identity. Pair signing with branch protection, secret scanning, and never committing credentials.
This is a core tutorial in Module 15 · Security of the REBASH Academy Git for Cloud & DevOps Engineers series — written for Cloud, DevOps, Platform, and SRE engineers.
Prerequisites¶
Learning Objectives¶
By the end of this tutorial, you will be able to:
- Configure SSH commit signing
- Verify with
git log --show-signature - Explain required signed commits on protected branches
- List secrets that must never enter history
- Outline response if a secret is committed
Architecture¶
This topic’s control points and relationships are shown below.
Theory¶
What¶
Git security combines cryptography and platform controls. Signed commits and tags (GPG, SSH, or X.509 signing) prove authorship integrity. Branch protection, CODEOWNERS, secret scanning, push protection, and least-privilege tokens reduce the chance that bad or spoofed changes reach main.
Why¶
Unsigned history can be rewritten or attributed falsely in social-engineering scenarios. Secrets in Git are a leading cloud breach pattern — assume anything committed is eventually exfiltrated. DevOps repos that deploy production need stronger defaults than hobby projects.
How it works¶
You configure a signing key, enable commit.gpgsign or SSH signing, and let the host verify badges on commits. Branch protection blocks direct pushes and requires reviews plus CI. Secret scanning alerts (and push protection blocks) known credential patterns. CI should prefer OIDC federation to cloud roles over long-lived static keys. If a secret is committed: rotate first, then scrub history with purpose-built tools (git filter-repo / BFG) under an incident process — never “delete the file in a new commit” as the only step.
| Control | Purpose |
|---|---|
| Signed commits/tags | Authorship integrity |
| Branch protection | No direct push to main |
| CODEOWNERS | Path-based review |
| Secret scanning / push protection | Stop credential leaks |
| Fine-grained PATs / OIDC | Safer CI auth |
Key concepts¶
- Verify signatures in clone policies for sensitive repos
- History rewrite after leaks is an org-wide coordination event
- Deploy keys vs GitHub Apps — scope automation narrowly
- Dependency and Action pinning — adjacent supply-chain controls
Common pitfalls¶
- Rotating a leaked key but leaving the old commit publicly readable without rewrite/incident notes
- Signing commits while still allowing unprotected force-pushes
- Broad classic PATs in shared CI secrets
- Committing
.env“temporarily” on a feature branch
Hands-on Lab¶
Create a workspace for this tutorial.
Focus: document SSH signing setup and inspect commit metadata
Step 1 – Signing checklist + baseline commit¶
git init
git config user.name "REBASH Learner"
git config user.email "learner@rebash.local"
cat > signing-notes.md << 'EOF'
# Signed commits
- git config gpg.format ssh
- git config user.signingkey ~/.ssh/id_ed25519.pub
- git config commit.gpgsign true
- Verify with: git log --show-signature
EOF
echo "signed-lab" > README.md
git add README.md signing-notes.md
git commit -m "docs: signing notes (enable SSH signing when keys exist)"
git log -1 --format='%H %G? %s'
Step 2 – Inspect commit headers¶
Final step – Cleanup note¶
Validation¶
- Lab commands run under
~/rebash-git/module-15/ - You can explain each Theory section in your own words
- You used modern tooling where it applies to this topic
- You can describe one production failure mode for this topic
Code Walkthrough¶
Production practice for Signed Commits and Git Security always combines:
- Inspect before you change (status, plan, logs, dry-run)
- Prefer reversible, documented changes (Git, IaC, drop-ins, version pins)
- Capture evidence (command output, pipeline logs) for handovers
- Prefer current tools and APIs over legacy shortcuts
- Least privilege — escalate credentials only when required
Keep runbooks short enough to follow under pressure. Automate checks; keep humans for judgement.
Security Considerations¶
- Treat credentials and tokens for git as privileged — never commit them
- Prefer short-lived auth (OIDC, roles, SSO) over long-lived keys
- Validate blast radius before apply/deploy/delete operations
- Restrict who can approve production changes
- Collect audit logs; limit who can read sensitive traces
Common Mistakes¶
Rotating a leaked key but leaving the old commit publicly readable without rewrite/inciden
Validate assumptions against the Theory section and official docs before changing production.
Signing commits while still allowing unprotected force-pushes
Lab shortcuts (open security groups, admin roles, skip approvals) must not ship unchanged.
Changing production without a rollback path
Always know how to revert (previous artefact, prior release, state rollback, DNS failback).
Best Practices¶
- Encode Signed Commits and Git Security changes as code and review them in pull requests
- Pin versions (images, modules, actions, provider plugins)
- Separate environments with clear promotion gates
- Alert on symptoms with runbooks attached
- Destroy lab resources; tag everything with owner and expiry where possible
Troubleshooting¶
| Symptom | Likely cause | Fix |
|---|---|---|
| Auth / permission denied | Wrong identity, policy, or scope | Check caller identity, roles, and least-privilege policies |
| Timeout / no route | Network, DNS, security group, or endpoint | Trace path, DNS, and allow-lists before retrying |
| Drift / unexpected plan | Manual change or wrong state/workspace | Reconcile desired vs actual; avoid click-ops on managed resources |
| Pipeline/job red | Flaky step, cache, or missing secret | Read failing step logs; bisect recent workflow/config changes |
| Cost spike | Idle load balancer, NAT, oversized compute | Inventory billable resources; stop/delete labs promptly |
Summary¶
Signed Commits and Git Security is essential for Cloud and DevOps engineers working with git. Practise the lab until the inspection and change path is muscle memory, then continue the track.
Interview Questions¶
- Why sign commits/tags in an enterprise?
- SSH signing versus GPG — trade-offs?
- How do you verify signatures in git log?
- What does commit signing not prove?
- How do web-of-trust / key directories fit?
Sample answer — question 2
Check user.signingkey, gpg.format, and whether the public key is registered on the host.
Sample answer — question 4
Signing keys are high value — protect them and revoke promptly on loss. Signing does not replace code review.