Iron Bank Container Signatures

The Iron Bank signs containers with the following certificate, signed by the Platform One CA.

cosign-certificate.pem:

cosign-publickey.pem

-----BEGIN PUBLIC KEY-----
MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAE7CjMGH005DFFz6mffqTIGurBt6fL
UfTZxuEDFRBS8mFJx1xw8DEVvjMibLTtqmAoJxUmzmGFgzz+LV875syVEg==
-----END PUBLIC KEY-----

Verifying a Signature

To verify a signature, make sure you have cosign installed. The path to the certificate file can be a URL or a file path.

If using Cosign 1.x

cosign verify --certificate-chain cosign-ca-bundle.pem --cert cosign-certificate.pem registry1.dso.mil/ironbank/redhat/ubi/ubi9:9.3

cosign verify \
--certificate-chain cosign-ca-bundle.pem \
--cert cosign-certificate.pem \
registry1.dso.mil/ironbank/redhat/ubi/ubi9:9.3

If using Cosign 2.x

  cosign verify \
  --key cosign-publickey.pem registry1.dso.mil/ironbank/suse/bci/bci-base:15.4 \
  --insecure-ignore-tlog=true

    cosign verify \
    --certificate-identity 'ironbank@dsop.io' --certificate-oidc-issuer-regexp '.*' \
    --certificate 'cosign-certificate.pem' \
    --certificate-chain 'cosign-ca-bundle.pem' \
    --signature-digest-algorithm=sha256 --insecure-ignore-tlog --insecure-ignore-sct=true registry1.dso.mil/ironbank/redhat/ubi/ubi9:9.3

A successful verify command will display the following

Verification for registry1.dso.mil/ironbank/redhat/ubi/ubi9:9.3 --
The following checks were performed on each of these signatures:
  - The cosign claims were validated
  - The signatures were verified against the specified public key

{"critical":{"identity":{"docker-reference":"registry1.dso.mil/ironbank/redhat/ubi/ubi9"},"image":{"docker-manifest-digest":"sha256:ec1cac395b78158812d0e670e1843b90faf4e933925b7e1c41f1c2f3ff06ff56"},"type":"cosign container image signature"},"optional":{"Subject":"ironbank@dsop.io"}}

Pulling Cosign Artifacts

Beyond creating image signatures, Cosign is used to generate additional artifacts in support of software supply chain security, such as image SBOMs and Attestations.

These artifacts, as well as their own signature artifacts, can be downloaded and verified using tools such as cosign and oras, as described in the following sections.

If using cosign download [command], the output will be sent to stdout. It is recommended to use either --output-file or pipe this output to another command.

Signature

The easiest way to access a signature is to use cosign download signature

cosign download signature <image uri>

Attestations

Attestation artifacts have tags ending in .att. Cosign attestations provide a means of associating arbitrary artifacts, such as SBOMs, to OCI images in registries. IronBank attaches SBOMs generated by syft as attestations using the follwoing predicateTypes:

cyclonedx
spdx
spdxjson

The payloads (i.e. the actual attestation content) for these predicateTypes are the SBOMs for the image, formatted in accordance with the predicateType. You can read more about these predicateTypes here.

Additonally, IronBank creates two custom predicates and attaches these as attestations to all images in registry1. The predicateType for these attestations are:

https://vat.dso.mil/api/p1/predicate/beta1
https://repo1.dso.mil/dsop/dccscr/-/raw/master/hardening%20manifest/README.md

These custom predicates have payloads that contain the VAT API response returned by VAT as part of the image pipeline and the hardening_manifest.json as payloads respectively. These predicates are discussed in further detail in the following sections.

VAT Response Predicate

The VAT response predicate contains the response receieved from the VAT API as part of the IronBank pipeline. The response is received when POSTing scan results, the hardening_manifest.yaml, and other compliance data to VAT.

This response and the predicate payload is forms acts as a signed, offline record attesting that the image has been run through the IronBank pipeline and submitted to VAT, and contains the VAT's compliance check results for wider distribution.

hardening_manifest.json Predicate

The hardening_manifest.json predicate contains a json-encoded copy of the hardening_manifest.yaml, along with the LICENSE, README.md, and access_logs as a payload. This predicate provides useful metadata about a given image that may not be relevent to VAT, and is therefore not contained in the VAT response predicate.

Verifying Attestations

Attestations, like the images themselves, are signed by Cosign. These signatures, which are attached to each attestation's DSSE envelope, can be validated using the following command:

cosign verify-attestation \
--type (slsaprovenance|link|spdx|spdxjson|cyclonedx|vuln|https://vat.dso.mil/api/p1/predicate/beta1|https://repo1.dso.mil/dsop/dccscr/-/raw/master/hardening%20manifest/README.md)
--output-file cosign-attestation.json \
--certificate-chain cosign-ca-bundle.pem \
--cert cosign-certificate.pem \
registry1.dso.mil/ironbank/docker/scratch:ironbank

Note: Because each attestation is individually added to the .att OCI artifact as DSSE envelopes, each envelope has its own signature. Therefore each attestation's signature must be validated individually.

Downloading and Parsing Attestations

The attestations for any given image in Registry1 contain a body of evidence including access logs, SBOMs, LICENSE files, and hardening_manifest.yaml content. In order to download and parse these, use the following script.

#!/bin/bash
image=registry1.dso.mil/ironbank/redhat/ubi/ubi9:9.3

declare -a predicate_types=("https://vat.dso.mil/api/p1/predicate/beta1" "https://repo1.dso.mil/dsop/dccscr/-/raw/master/hardening%20manifest/README.md" "https://spdx.dev/Document" "https://cyclonedx.org/bom" "https://cyclonedx.org/schema")

for predicate_type in "${predicate_types[@]}"; do
  case $predicate_type in
    'https://vat.dso.mil/api/p1/predicate/beta1')
      filename=vat_response.json
      ;;
    'https://repo1.dso.mil/dsop/dccscr/-/raw/master/hardening%20manifest/README.md')
      filename=hardening_manifest.json
      ;;
    'https://spdx.dev/Document')
      filename=spdx.json
      ;;
    'https://cyclonedx.org/bom')
      filename=cyclonedx-bom.json
      ;;
    'https://cyclonedx.org/schema')
      filename=cyclonedx-schema.json
      ;;
  esac

  cos=$(cosign download attestation $image | jq -r '(.payload | @base64d)' | jq -c 'select( .predicateType == "'$predicate_type'")')
  if [[ $(echo $cos | wc -c | awk '{print $1}') -gt 2 ]]; then
    echo $predicate_type
    echo $cos | jq > $filename
  fi
done

This script will cycle through the attestations, decode them, and stores them as separate files on disk named according to the predicateType.

Public Key Infrastructure

The following CA bundle cert may be used to validate Iron Bank certificate authenticity.