Secure Supply Chain with Sigstore, Cosign & SLSA Framework

1. Introduction: The Supply Chain Problem

Modern software delivery pipelines rely on a complex web of open-source dependencies, CI/CD automation, container registries, and orchestration platforms.
This interconnected ecosystem introduces risks such as:

• Compromised build environments
• Tampered container images
• Malicious third-party dependencies
• Lack of verifiable provenance

Example:
The SolarWinds and Codecov supply chain attacks showed that even signed software can’t be trusted if the build process itself is compromised.

Hence, security is shifting “left” — directly into the build and packaging stages, where trust must begin.

2. Understanding Sigstore and Cosign

 Sigstore Overview

Sigstore is an open-source project (backed by Google, Red Hat, and the Linux Foundation) designed to make digital signing and verification of software artifacts easier and more transparent.

It eliminates the traditional complexity of PKI (Private Key Infrastructure) by providing:

• Keyless signing using OIDC identities (e.g., GitHub Actions, Google, etc.)
• Public transparency logs via Rekor (immutable log for signed metadata)
• Fulcio CA for ephemeral certificate issuance

 Cosign: Simplifying Container Signing

Cosign (by Sigstore) allows you to sign, verify, and store container image signatures directly inside container registries — right next to the images they secure.

Example workflow:

# Sign a container image

cosign sign --keyless ghcr.io/org/app:latest

# Verify its authenticity

cosign verify ghcr.io/org/app:latest

When integrated into CI/CD (e.g., GitHub Actions, Jenkins, or ArgoCD), Cosign ensures only trusted, verified artifacts are deployed into production.

3. The Role of the SLSA Framework

 What is SLSA?

SLSA (Supply-chain Levels for Software Artifacts), pronounced “salsa,” is a security framework by Google that defines graduated levels of supply chain integrity — from source to production.

It provides a structured approach with four levels of assurance:

Goal: Make it extremely hard for attackers to inject malicious code or modify build outputs without detection.

 4. Integrating Sigstore, Cosign & SLSA in DevOps Pipelines

Example Flow:

1. Developer commits code → GitHub Action triggers build
2. Build produces image + provenance metadata (SLSA)
3. Cosign keylessly signs the image → stores signature in registry
4. Rekor logs the signature and metadata publicly
5. Deployment stage uses Cosign verify before applying manifests
6. ArgoCD or Flux enforces admission control (deny unsigned images)

 CI/CD Integration Example (GitHub Actions)

name: Secure Build Pipeline 

on: [push]

jobs:

  build-sign:

    runs-on: ubuntu-latest

    steps:

      - uses: actions/checkout@v4

      - name: Build Docker image

        run: docker build -t ghcr.io/org/app:${{ github.sha }} .

      - name: Sign with Cosign

        run: cosign sign --keyless ghcr.io/org/app:${{ github.sha }}

      - name: Upload Provenance (SLSA)

        uses: slsa-framework/slsa-github-generator@v1

This ensures end-to-end traceability and trust, linking every artifact to a specific commit and verified signer identity.

 5. Verification and Policy Enforcement

You can enforce security policies using Kubernetes Admission Controllers, OPA/Gatekeeper, or Kyverno to ensure:

• Only signed images are deployed.
• Signatures must be verifiable via Sigstore.
• Provenance metadata must match build source.

Example Kyverno Policy:

apiVersion: kyverno.io/v1

kind: ClusterPolicy

metadata:

  name: verify-image-signature

spec:

  validationFailureAction: enforce

  rules:

  - name: check-cosign-signature

    match:

      resources:

        kinds: ["Pod"]

    verifyImages:

    - image: "ghcr.io/org/*"

      keyless: true

      issuer: "https://token.actions.githubusercontent.com"

 6. The Business Impact

Implementing Sigstore + SLSA strengthens:

• Regulatory compliance (e.g., NIST SSDF, ISO 27001)
• Incident response readiness through transparent logs
• Developer trust in CI/CD pipelines
• Operational resilience across environments

It turns “trust by assumption” into trust by verification.

7. Conclusion

Container signing and provenance verification are no longer optional — they’re fundamental to modern DevSecOps.
By combining Sigstore’s simplicity, Cosign’s flexibility, and SLSA’s structured assurance model, organizations can build a verifiable chain of trust across every stage of their software supply chain.

Your CI/CD pipeline becomes not just fast — but provably secure.