Image Signing and Verification

Image Signing and Verification

Image signing ensures image integrity and authenticity throughout the distribution pipeline. Docker Content Trust (DCT) implements The Update Framework (TUF) for image signing. Signatures prevent tampering and verify publisher identity. However, signature verification requires explicit enablement and key management infrastructure.

Implementing image signing requires key management processes. Root keys provide ultimate signing authority and require offline storage. Repository keys sign specific images and tags. Delegation enables distributed signing authority. Key rotation procedures handle compromised or expired keys. Organizations need documented processes for key lifecycle management.

#!/bin/bash
# Example: Docker Content Trust implementation

# Enable Docker Content Trust
export DOCKER_CONTENT_TRUST=1
export DOCKER_CONTENT_TRUST_SERVER=https://notary.example.com

# Initialize repository with root key
docker trust key generate root-key
docker trust signer add --key cert.pem admin registry.example.com/myapp

# Sign and push image
docker tag myapp:latest registry.example.com/myapp:v1.0.0
docker push registry.example.com/myapp:v1.0.0

# Verify image signature
docker trust inspect --pretty registry.example.com/myapp:v1.0.0

# Rotate keys periodically
docker trust key rotate registry.example.com/myapp --key new-key.pem

Supply chain security extends beyond image signing to include build provenance. Software Bill of Materials (SBOM) documents image contents and origins. In-toto provides attestations about build steps and artifact flows. These mechanisms enable verification of entire build pipelines, not just final artifacts. Organizations should implement comprehensive supply chain security matching their risk profiles.