What it does. 'Implements code signing for build artifacts (binaries, packages, containers) Part of mukul975/Anthropic-Cybersecurity-Skills (817 security skills) (mukul975/Anthropic-Cybersecurity-Skills).

Upstream	mukul975/Anthropic-Cybersecurity-Skills
Skill file	skills/implementing-code-signing-for-artifacts/SKILL.md
License	Apache-2.0 (skill folder LICENSE)
Author	mukul975
Fetched	2026-09-10

Install

• npx skills add mukul975/Anthropic-Cybersecurity-Skills --skill implementing-code-signing-for-artifacts, or copy the skill folder into ~/.claude/skills/implementing-code-signing-for-artifacts/.
• Raw file: curl -sL https://raw.githubusercontent.com/mukul975/Anthropic-Cybersecurity-Skills/HEAD/skills/implementing-code-signing-for-artifacts/SKILL.md

SKILL.md (verbatim)

name: implementing-code-signing-for-artifacts
description: 'Implements code signing for build artifacts (binaries, packages, containers)
  using GPG, Sigstore, and platform-specific signing tools, establishing trust chains
  and verifying signatures in deployment pipelines. Use when establishing artifact
  integrity checks against supply-chain tampering, proving authenticity to customers,
  building zero-trust pipelines that reject unsigned artifacts, or meeting SLSA Level
  2+ provenance requirements.

  '
domain: cybersecurity
subdomain: devsecops
tags:
- devsecops
- cicd
- code-signing
- supply-chain
- sigstore
- secure-sdlc
version: 1.0.0
author: mahipal
license: Apache-2.0
nist_csf:
- PR.PS-01
- GV.SC-07
- ID.IM-04
- PR.PS-04
mitre_attack:
- T1195
- T1554
- T1059.004
- T1610
- T1611

Implementing Code Signing for Artifacts

When to Use

• When establishing artifact integrity verification to prevent supply chain tampering
• When compliance requires cryptographic proof that build artifacts are authentic and unmodified
• When distributing software to customers who need to verify publisher identity
• When implementing zero-trust deployment pipelines that reject unsigned artifacts
• When meeting SLSA Level 2+ requirements for provenance and integrity

Do not use for encrypting artifacts (signing provides integrity, not confidentiality), for container image signing specifically (use cosign), or for source code authentication (use commit signing).

Prerequisites

• GPG key pair for traditional signing or Sigstore account for keyless signing
• Code signing certificate from a Certificate Authority for public distribution
• CI/CD pipeline with access to signing keys or identity provider
• Verification infrastructure in deployment pipelines

Workflow

Step 1: Generate and Manage Signing Keys

# Generate GPG key for artifact signing
gpg --full-generate-key --batch <<EOF
Key-Type: eddsa
Key-Curve: ed25519
Subkey-Type: eddsa
Subkey-Curve: ed25519
Name-Real: CI Build System
Name-Email: ci-signing@company.com
Expire-Date: 1y
%no-protection
EOF

# Export public key for distribution
gpg --armor --export ci-signing@company.com > signing-key.pub

# Export private key for CI/CD (store in secrets manager)
gpg --armor --export-secret-keys ci-signing@company.com > signing-key.priv

Step 2: Sign Build Artifacts in CI/CD

# .github/workflows/build-sign.yml
name: Build and Sign

on:
  push:
    tags: ['v*']

jobs:
  build-sign:
    runs-on: ubuntu-latest
    permissions:
      contents: write
      id-token: write  # For Sigstore keyless signing
    steps:
      - uses: actions/checkout@v4

      - name: Build artifacts
        run: |
          make build
          sha256sum dist/* > dist/checksums.sha256

      - name: Import GPG Key
        run: |
          echo "${{ secrets.GPG_PRIVATE_KEY }}" | gpg --batch --import
          gpg --list-secret-keys

      - name: Sign artifacts
        run: |
          for file in dist/*; do
            gpg --detach-sign --armor --local-user ci-signing@company.com "$file"
          done

      - name: Install cosign for keyless signing
        uses: sigstore/cosign-installer@v3

      - name: Keyless sign with Sigstore
        run: |
          for file in dist/*.tar.gz; do
            cosign sign-blob "$file" \
              --output-signature "${file}.sig" \
              --output-certificate "${file}.cert" \
              --yes
          done

      - name: Create Release with signed artifacts
        uses: softprops/action-gh-release@v2
        with:
          files: |
            dist/*
            dist/*.asc
            dist/*.sig
            dist/*.cert

Step 3: Verify Signatures in Deployment Pipeline

# Verify GPG signature
gpg --import signing-key.pub
gpg --verify artifact.tar.gz.asc artifact.tar.gz

# Verify Sigstore keyless signature
cosign verify-blob artifact.tar.gz \
  --signature artifact.tar.gz.sig \
  --certificate artifact.tar.gz.cert \
  --certificate-identity ci-signing@company.com \
  --certificate-oidc-issuer https://token.actions.githubusercontent.com

# Verify checksums
sha256sum --check checksums.sha256

Step 4: Sign npm Packages with Provenance

{
  "scripts": {
    "prepublishOnly": "npm run build && npm run test"
  },
  "publishConfig": {
    "provenance": true
  }
}

# Publish npm package with provenance attestation
npm publish --provenance

Key Concepts

Term	Definition
Code Signing	Cryptographic process of signing software artifacts to verify publisher identity and artifact integrity
Detached Signature	Signature stored in a separate file from the artifact, allowing independent distribution
Keyless Signing	Sigstore's approach using short-lived certificates tied to OIDC identities instead of long-lived keys
Provenance	Metadata describing how, where, and by whom an artifact was built
Transparency Log	Append-only log (Rekor) that records all signing events for public auditability
Trust Chain	Hierarchical chain from root CA to signing certificate establishing trust in the signer's identity
SLSA	Supply-chain Levels for Software Artifacts — framework defining levels of supply chain security

Tools & Systems

• GPG/PGP: Traditional asymmetric cryptography tool for signing and verifying artifacts
• Sigstore (cosign): Modern keyless signing infrastructure using OIDC identity and transparency logs
• Rekor: Sigstore's transparency log recording all signing events immutably
• Fulcio: Sigstore's certificate authority issuing short-lived certificates bound to OIDC identities
• notation: Microsoft's artifact signing tool for OCI registries (Project Notary v2)

Common Scenarios

Scenario: Establishing Signed Release Pipeline

Context: An open-source project needs to sign release artifacts so users can verify authenticity and detect tampering.

Approach:

1. Use Sigstore keyless signing in GitHub Actions (no key management overhead)
2. Sign all release binaries with cosign sign-blob using OIDC identity
3. Generate and sign checksums file for bulk verification
4. Upload signatures, certificates, and checksums alongside release artifacts
5. Document verification instructions in the project README
6. Add verification step to the Homebrew formula or apt repository

Pitfalls: GPG key compromise requires revoking and re-signing all artifacts. Sigstore keyless signing avoids this by using ephemeral keys. Long-lived signing keys in CI/CD secrets are a supply chain risk if the CI system is compromised.

Output Format

Artifact Signing Report
========================
Pipeline: Build and Sign v2.3.0
Date: 2026-02-23
Signing Method: Sigstore Keyless + GPG

SIGNED ARTIFACTS:
  app-v2.3.0-linux-amd64.tar.gz
    GPG:      PASS (ci-signing@company.com, EdDSA/Ed25519)
    Sigstore: PASS (Rekor entry: 24658135, Fulcio cert issued)
    SHA256:   a1b2c3d4...

  app-v2.3.0-darwin-arm64.tar.gz
    GPG:      PASS
    Sigstore: PASS (Rekor entry: 24658136)
    SHA256:   e5f6g7h8...

  checksums.sha256
    GPG:      PASS (detached signature)

TRANSPARENCY LOG:
  Entries recorded: 3
  Log index range: 24658135-24658137
  Verification: https://search.sigstore.dev

Other files in this skill

• LICENSE
• assets/template.md
• references/api-reference.md
• references/standards.md
• references/workflows.md
• scripts/agent.py
• scripts/process.py

assets/template.md (verbatim)

Code Signing Templates

GitHub Actions: Build, Sign, and Release

name: Signed Release
on:
  push:
    tags: ['v*']

jobs:
  release:
    runs-on: ubuntu-latest
    permissions:
      contents: write
      id-token: write
    steps:
      - uses: actions/checkout@v4
      - name: Build
        run: make build-all
      - uses: sigstore/cosign-installer@v3
      - name: Sign artifacts
        run: |
          for f in dist/*.tar.gz; do
            cosign sign-blob "$f" --output-signature "${f}.sig" --output-certificate "${f}.cert" --yes
          done
          sha256sum dist/*.tar.gz > dist/checksums.sha256
      - uses: softprops/action-gh-release@v2
        with:
          files: dist/*

Verification Script

#!/bin/bash
set -euo pipefail
# verify-release.sh <artifact> <signature> <certificate>
ARTIFACT="$1"
SIGNATURE="$2"
CERTIFICATE="$3"

echo "Verifying: $ARTIFACT"
sha256sum "$ARTIFACT"

cosign verify-blob "$ARTIFACT" \
  --signature "$SIGNATURE" \
  --certificate "$CERTIFICATE" \
  --certificate-identity "https://github.com/org/repo/.github/workflows/release.yml@refs/tags/*" \
  --certificate-oidc-issuer "https://token.actions.githubusercontent.com"

echo "Verification: PASSED"

references/api-reference.md (verbatim)

API Reference: Code Signing Verification Agent

Dependencies

Library	Version	Purpose
cryptography	>=41.0	Ed25519 key generation, signing, and verification

CLI Usage

# Generate keypair
python scripts/agent.py --generate-keys --output-dir /keys/

# Sign artifact
python scripts/agent.py --sign build/app.tar.gz --private-key /keys/signing_key.pem

# Verify artifacts
python scripts/agent.py \
  --artifacts build/app.tar.gz build/lib.so \
  --public-key /keys/signing_key.pub \
  --output-dir /reports/

Functions

generate_ed25519_keypair(output_dir) -> dict

Calls Ed25519PrivateKey.generate(), serializes to PEM using private_bytes() and public_bytes().

sign_artifact(file_path, private_key_path) -> dict

Loads PEM key via serialization.load_pem_private_key(), calls private_key.sign(data). Writes 64-byte signature to .sig file.

verify_signature(file_path, signature_path, public_key_path) -> dict

Loads public key, calls public_key.verify(signature, data). Catches InvalidSignature.

verify_cosign_signature(image) -> dict

Runs cosign verify <image> via subprocess for container image signature verification.

batch_verify(artifacts, public_key_path) -> list

Verifies multiple artifacts against the same public key.

cryptography API Used

Class/Method	Purpose
Ed25519PrivateKey.generate()	Generate signing keypair
private_key.sign(data)	Sign data (returns 64 bytes)
public_key.verify(signature, data)	Verify signature
serialization.load_pem_private_key()	Load PEM private key

Output Schema

{
  "summary": {"total": 3, "valid": 2, "invalid": 1},
  "verifications": [{"file": "app.tar.gz", "valid": true, "algorithm": "Ed25519"}]
}

references/standards.md (verbatim)

Standards Reference: Code Signing for Artifacts

SLSA Framework

Level 1: Build Provenance

• Document the build process (source, builder, dependencies)
• Provenance metadata available for all artifacts

Level 2: Signed Provenance

• Build provenance is signed by the build platform
• Signatures tied to authenticated builder identity

Level 3: Hardened Build Platform

• Build process runs on a hardened, isolated platform
• Provenance is non-falsifiable by the build service

NIST SSDF (SP 800-218)

PS.2: Provide Mechanism for Verifying Software Release Integrity

• PS.2.1: Make integrity verification information available to consumers
• Code signing provides cryptographic proof of artifact integrity
• Transparency logs provide public auditability of signing events

PW.4: Reuse Existing, Well-Secured Software

• Verify signatures of third-party dependencies before integration
• Establish trust anchors for acceptable signing identities

CIS Software Supply Chain Security

Artifacts (AR) Controls

• AR-1: Sign all build artifacts using cryptographic signatures
• AR-2: Verify artifact signatures before deployment
• AR-3: Use transparency logs for signing event auditability
• AR-4: Rotate signing keys on a defined schedule

Executive Order 14028

• Section 4(e): Agencies shall employ tools and processes to maintain trusted source code supply chains
• SBOM and artifact signing required for federal software suppliers
• Sigstore adoption recommended by CISA for open-source supply chain security

references/workflows.md (verbatim)

Workflow Reference: Code Signing for Artifacts

Signing Pipeline Flow

Build Artifacts
       │
       ▼
┌──────────────────┐
│ Generate          │
│ Checksums         │
└──────┬───────────┘
       │
       ├──────────────────────┐
       ▼                      ▼
┌──────────────┐    ┌──────────────┐
│ GPG Sign     │    │ Sigstore     │
│ (detached)   │    │ Keyless Sign │
└──────┬───────┘    └──────┬───────┘
       │                    │
       │                    ▼
       │            ┌──────────────┐
       │            │ Rekor Log    │
       │            │ Entry        │
       │            └──────┬───────┘
       │                    │
       └──────────┬─────────┘
                  ▼
       ┌──────────────────┐
       │ Publish Release  │
       │ + Signatures     │
       └──────────────────┘

Signing Methods Comparison

Method	Key Management	Identity	Verification	Best For
GPG	Manual key lifecycle	Key fingerprint	gpg --verify	Traditional projects
Sigstore Keyless	No keys to manage	OIDC identity	cosign verify-blob	Modern CI/CD
Code Signing Cert	CA-issued certificate	Organization name	Platform-specific	Windows/macOS apps
npm Provenance	Automated	GitHub Actions OIDC	npm audit signatures	npm packages

Back to mukul975/Anthropic-Cybersecurity-Skills (817 security skills) or Agent skills.