imag-prvn-vrfc-cosi

name	imag-prvn-vrfc-cosi
description	Sign and verify container image provenance using Sigstore Cosign with keyless OIDC-based signing, attestations, and Kubernetes admission enforcement.
domain	cybersecurity
subdomain	container-security
tags	["cosign","sigstore","image-signing","supply-chain","provenance","keyless","slsa"]
version	1.0
author	mahipal
license	Apache-2.0
nist_csf	["PR.PS-01","PR.IR-01","ID.AM-08","DE.CM-01"]

Implementing Image Provenance Verification with Cosign

Overview

Cosign is a Sigstore tool for signing, verifying, and attaching metadata to container images and OCI artifacts. It supports both key-based and keyless (OIDC) signing, integrates with Fulcio (certificate authority) and Rekor (transparency log), and enables supply chain security for container images.

When to Use

• When deploying or configuring implementing image provenance verification with cosign capabilities in your environment
• When establishing security controls aligned to compliance requirements
• When building or improving security architecture for this domain
• When conducting security assessments that require this implementation

Prerequisites

• Cosign CLI installed
• Docker or Podman for building images
• OCI-compliant container registry (Docker Hub, GHCR, GCR, ECR)
• OIDC provider account (GitHub, Google, Microsoft) for keyless signing

Installing Cosign

# Install via Go
go install github.com/sigstore/cosign/v2/cmd/cosign@latest

# Install via Homebrew
brew install cosign

# Install via script
curl -O -L "https://github.com/sigstore/cosign/releases/latest/download/cosign-linux-amd64"
sudo mv cosign-linux-amd64 /usr/local/bin/cosign
sudo chmod +x /usr/local/bin/cosign

# Verify installation
cosign version

Key-Based Signing

Generate Key Pair

# Generate cosign key pair (creates cosign.key and cosign.pub)
cosign generate-key-pair

# Generate key pair stored in KMS
cosign generate-key-pair --kms awskms:///alias/cosign-key
cosign generate-key-pair --kms gcpkms://projects/PROJECT/locations/LOCATION/keyRings/KEYRING/cryptoKeys/KEY
cosign generate-key-pair --kms hashivault://transit/keys/cosign

Sign Image with Key

# Sign an image
cosign sign --key cosign.key ghcr.io/myorg/myapp:v1.0.0

# Sign with annotations
cosign sign --key cosign.key \
  -a "build-id=12345" \
  -a "git-sha=$(git rev-parse HEAD)" \
  ghcr.io/myorg/myapp:v1.0.0