Senior LevelWeb Security & Cyber Defense
How do you enforce Container Image Signing using Cosign and Sigstore in Kubernetes?
❓ Interview Prompt: Explain Container Image Signing, Sigstore / Cosign, Keyless signing with Fulcio OIDC, Rekor transparency log, and Kyverno policy enforcement.
Protecting container registries against supply chain tampering using Sigstore / Cosign:
Keyless Image Signing Architecture:
1
Developer/CI authenticates via OIDC. Fulcio issues a short-lived signing certificate.
2
Cosign signs the OCI container image digest and uploads the signature to the registry.
3
Signature transparency log is recorded in Rekor.
4
Kyverno Policy (Kubernetes): Admission controller blocks container pods from launching unless signed by an authorized Sigstore identity!
Code Implementation Example
yaml
# Kyverno Policy Enforcing Cosign Container Image Signature Verification
apiVersion: kyverno.io/v1
kind: ClusterPolicy
metadata:
name: verify-image-signatures
spec:
validationFailureAction: Enforce
rules:
- name: verify-signature
match:
resources:
kinds: [Pod]
verifyImages:
- imageReferences: ["ghcr.io/mycompany/*"]
attestors:
- count: 1
entries:
- keys:
publicKeys: |-----BEGIN PUBLIC KEY-----...💡Kyverno cluster policy enforcing Cosign container image signature verification.
🎯 Interview Key Takeaway
Sign container images with Sigstore/Cosign and enforce signature verification policies in Kubernetes admission controllers.
#Cosign#Sigstore#Kyverno#Container Security#Senior
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