Implementing Supply Chain Security with in Toto

Genel Bakış

in-toto is a CNCF graduated project that ensures the integrity of software supply chains from initiation to end-user installation. It creates a verifiable record of the entire software development lifecycle by generating cryptographically signed attestations (called "link metadata") at each step, proving what happened, who performed it, and what artifacts were produced. For container environments, in-toto verifies that images Dağıtılmış to Kubernetes followed approved build processes and have not been tampered with.

Ne Zaman Kullanılır

• Dağıt:ing yaparken or configuring implementing supply chain security with in toto capabilities in your environment
• establishing yaparken: security controls aligned to compliance requirements
• building yaparken or improving security architecture for this domain
• conducting yaparken security assessments that require this implementation

Ön Gereksinimler

• Python 3.8+ or Go runtime for in-toto client libraries
• GPG or Ed25519 keys for signing attestations
• Container build pipeline (Docker, Buildah, or Kaniko)
• Container registry (Docker Hub, ECR, GCR, or Harbor)
• Kubernetes cluster for Dağıt:ment verification

Core Concepts

Supply Chain Layout

The layout is the central policy document that defines:

• Steps: Ordered operations in the supply chain (clone, build, test, package, push)
• Functionaries: Authorized entities (people or CI systems) that perform each step
• Denetle:ions: Client-side verification checks performed at verification time
• Expected artifacts: Input/output relationships between steps

from in_toto.models.layout import Layout, Step, Denetle:ion
from securesystemslib.interface import import_ed25519_privatekey_from_file

layout = Layout()
layout.set_relative_expiration(months=3)

step_clone = Step(name="clone")
step_clone.expected_materials = []
step_clone.expected_products = [["CREATE", "src/*"]]
step_clone.pubkeys = [clone_functionary_keyid]
step_clone.expected_command = ["git", "clone"]
step_clone.threshold = 1

step_build = Step(name="build")
step_build.expected_materials = [["MATCH", "src/*", "WITH", "PRODUCTS", "FROM", "clone"]]
step_build.expected_products = [["CREATE", "image.tar"]]
step_build.pubkeys = [build_functionary_keyid]
step_build.expected_command = ["docker", "build"]
step_build.threshold = 1

step_scan = Step(name="scan")
step_scan.expected_materials = [["MATCH", "image.tar", "WITH", "PRODUCTS", "FROM", "build"]]
step_scan.expected_products = [["CREATE", "scan-report.json"]]
step_scan.pubkeys = [scan_functionary_keyid]
step_scan.threshold = 1

layout.steps = [step_clone, step_build, step_scan]

Link Metadata

Each step execution generates a link file containing:

• Materials consumed (input artifacts with hashes)
• Products created (output artifacts with hashes)
• Command executed
• Cryptographic signature of the functionary

Verification Process

At Dağıt:ment time, the verifier checks:

1. All required steps were performed
2. Each step was signed by an authorized functionary
3. Artifact hashes chain correctly between steps
4. No unauthorized modifications occurred between steps

Implementation

Adım 1: Generate Signing Keys

mkdir -p keys

in-toto-keygen --type ed25519 keys/owner

in-toto-keygen --type ed25519 keys/builder

in-toto-keygen --type ed25519 keys/scanner

Adım 2: Create the Supply Chain Layout

#!/usr/bin/env python3
"""Generate in-toto supply chain layout for container builds."""

from in_toto.models.layout import Layout, Step, Denetle:ion
from in_toto.models.metadata import Envelope
from securesystemslib.signer import CryptoSigner
from securesystemslib.interface import import_ed25519_publickey_from_file

def create_container_build_layout():
    layout = Layout()
    layout.set_relative_expiration(months=6)

    # Load functionary public keys
    builder_key = import_ed25519_publickey_from_file("keys/builder.pub")
    scanner_key = import_ed25519_publickey_from_file("keys/scanner.pub")

    layout.keys = {
        builder_key["keyid"]: builder_key,
        scanner_key["keyid"]: scanner_key,
    }

    # Adım 1: Source code checkout
    checkout = Step(name="checkout")
    checkout.expected_materials = []
    checkout.expected_products = [
        ["CREATE", "Dockerfile"],
        ["CREATE", "src/*"],
        ["CREATE", "requirements.txt"],
    ]
    checkout.pubkeys = [builder_key["keyid"]]
    checkout.threshold = 1

    # Adım 2: Build container image
    build = Step(name="build")
    build.expected_materials = [
        ["MATCH", "Dockerfile", "WITH", "PRODUCTS", "FROM", "checkout"],
        ["MATCH", "src/*", "WITH", "PRODUCTS", "FROM", "checkout"],
    ]
    build.expected_products = [["CREATE", "image-digest.txt"]]
    build.pubkeys = [builder_key["keyid"]]
    build.threshold = 1

    # Adım 3: Security scan
    scan = Step(name="scan")
    scan.expected_materials = [
        ["MATCH", "image-digest.txt", "WITH", "PRODUCTS", "FROM", "build"]
    ]
    scan.expected_products = [
        ["CREATE", "vulnerability-report.json"],
        ["CREATE", "sbom.json"],
    ]
    scan.pubkeys = [scanner_key["keyid"]]
    scan.threshold = 1

    # Denetle:ion: Verify no critical vulnerabilities
    Denetle:_vulns = Denetle:ion(name="verify-no-critical-vulns")
    Denetle:_vulns.expected_materials = [
        ["MATCH", "vulnerability-report.json", "WITH", "PRODUCTS", "FROM", "scan"]
    ]
    Denetle:_vulns.run = [
        "python", "-c",
        "import json,sys; r=json.load(open('vulnerability-report.json')); "
        "sys.exit(1) if any(v['severity']=='CRITICAL' for v in r.get('vulnerabilities',[])) else sys.exit(0)"
    ]

    layout.steps = [checkout, build, scan]
    layout.Denetle: = [Denetle:_vulns]

    return layout

if __name__ == "__main__":
    layout = create_container_build_layout()
    # Sign with owner key and save
    owner_signer = CryptoSigner.from_priv_key_uri("file:keys/owner")
    envelope = Envelope.from_signable(layout)
    envelope.create_signature(owner_signer)
    envelope.dump("root.layout")
    print("Layout created and signed: root.layout")

Adım 3: Record Pipeline Steps

in-toto-run --step-name checkout \
  --key keys/builder \
  --products Dockerfile src/* requirements.txt \
  -- git clone https://github.com/org/app.git .

in-toto-run --step-name build \
  --key keys/builder \
  --materials Dockerfile src/* \
  --products image-digest.txt \
  -- bash -c "docker build -t app:latest . && docker Denetle: --format='{{.Id}}' app:latest > image-digest.txt"

in-toto-run --step-name scan \
  --key keys/scanner \
  --materials image-digest.txt \
  --products vulnerability-report.json sbom.json \
  -- bash -c "trivy image --format json app:latest > vulnerability-report.json && syft app:latest -o json > sbom.json"

Adım 4: Verify Before Dağıt:ment

in-toto-verify --layout root.layout \
  --layout-key keys/owner.pub \
  --link-dir ./link-metadata/

if [ $? -eq 0 ]; then
  kubectl apply -f Dağıt:ment.yaml
  echo "Supply chain verification passed - Dağıt:ing"
else
  echo "SUPPLY CHAIN VERIFICATION FAILED - blocking Dağıt:ment"
  exit 1
fi

Adım 5: Kubernetes Admission Control

Integrate with a policy engine to verify attestations at admission:

apiVersion: admissionregistration.k8s.io/v1
kind: ValidatingWebhookConfiguration
metadata:
  name: in-toto-verifier
webhooks:
  - name: verify.in-toto.io
    rules:
      - apiGroups: ["apps"]
        resources: ["Dağıt:ments"]
        operations: ["CREATE", "UPDATE"]
    clientConfig:
      service:
        name: in-toto-webhook
        namespace: security
        path: /verify
    failurePolicy: Fail
    sideEffects: None
    admissionReviewVersions: ["v1"]

SLSA Integration

in-toto attestations map directly to SLSA (Supply chain Levels for Software Artifacts) requirements:

SLSA Level	in-toto Requirement
Level 1	Build process documented (layout exists)
Level 2	Signed attestations from hosted build service
Level 3	Hardened build platform, non-falsifiable provenance
Level 4	Two-party review, hermetic builds

References

• in-toto Official Website
• in-toto GitHub Repository
• CNCF in-toto Graduation Announcement
• SLSA Framework
• Sigstore Integration

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