Enhancing Supply Chain Security: Signing SBOMs with CycloneDX

In an era where supply chain attacks are becoming increasingly sophisticated, ensuring the integrity and authenticity of your software components is paramount. CycloneDX introduces new signature capabilities that enable developers and DevOps engineers to sign Software Bill of Materials (SBOM) files, adding an essential layer of security to the software development lifecycle.

In this blog post, we will explore the importance of signing SBOMs, how to leverage CycloneDX to sign these files, and best practices for managing your signing keys.

Currently only XML SBOM files are supported using the CycloneDX-CLI tool. Therefore you would need to convert JSON file to XML, what is errorprone. Stay tuned to learn in our follow up blog post how to sign JSON SBOMs.

The Importance of Signing SBOMs

A Software Bill of Materials (SBOM) is a comprehensive list of components, libraries, and modules that make up a software application. It is an essential tool for managing dependencies, understanding potential vulnerabilities, and ensuring compliance with security policies. However, an SBOM is only as reliable as the environment in which it was generated and the security measures in place to protect it.

By signing an SBOM, you can:

1. Ensure Integrity: A signed SBOM guarantees that the contents have not been altered or tampered with since it was generated.
2. Prove Authenticity: Signing provides proof that the SBOM was created within a trusted environment, helping to establish trust between software producers and consumers.
3. Mitigate Supply Chain Attacks: By verifying the signature of an SBOM before using or deploying the associated artifacts, organizations can prevent the execution of malicious code that may have been introduced through tampered dependencies.

How to Sign an SBOM with CycloneDX

CycloneDX makes the process of signing an SBOM straightforward. Here are the steps you need to follow:

Step 1: Generate Key Pairs

Before you can sign an SBOM, you need to generate a pair of cryptographic keys: a private key for signing and a public key for verification. CycloneDX provides a simple command-line interface (CLI) to accomplish this:

This command generates a new key pair and saves the public key to public.key and the private key to private.key.

Step 2: Sign the SBOM

Once you have your keys, you can sign your SBOM using the cyclonedx-cli tool. Assuming you have an SBOM file named bom.xml, you can sign it with the following command:

This command loads your private key, reads the SBOM file, generates a signature, and appends a <Signature> tag to the end of the SBOM file.

Step 3: Verify the Signature

To ensure the integrity and authenticity of a signed SBOM, the signature can be verified using the corresponding public key:

./cyclonedx-cli verify all bom.xml --key-file=public.key
Loading public key...
Loading XML BOM...
Reading signatures...
Found 1 signatures...
Verifying signature 1... verified

All signatures verified

If the SBOM has not been tampered with, the verification process will confirm that the signature is valid.

Best Practices for Managing Signing Keys

Signing keys are a critical part of your security infrastructure. Here are some best practices for managing them:

Secure Storage

Private keys should be stored securely in a trusted environment. Use hardware security modules (HSMs) or secure key management services provided by cloud providers to store private keys.

Limited Access

Access to the private key should be restricted to the environments where SBOMs are generated. Avoid sharing the private key with third parties and ensure that only authorized personnel have access.

Regular Rotation

Periodically rotate your key pairs to minimize the risk of key compromise. Establish a key rotation policy that aligns with your organization's security requirements.

Public Key Distribution

Distribute your public key to all stakeholders who need to verify the integrity of your SBOMs. Ensure that the public key is accessible and verifiable by those who depend on your software.

Conclusion

The new signature capabilities of CycloneDX provide a robust mechanism for ensuring the integrity and authenticity of SBOMs. By signing SBOMs, developers and DevOps engineers can enhance their supply chain security, prevent tampering, and build trust with their software consumers. Implementing a secure process for generating, signing, and verifying SBOMs, along with proper key management practices, is essential for maintaining the integrity of your software supply chain.

As supply chain attacks continue to evolve, tools like CycloneDX and its new signature capabilities will play a crucial role in defending against these threats. Embrace these new features and fortify your software development practices to safeguard your applications and users.