Unlocking the Power of Code Signing: A Guide to Strengthening Software Security

Unlocking the Power of Code Signing: A Guide to Strengthening Software Security

Troy Cogburn

Chief Technology Evangelist

April 22, 2024


Code signing is increasingly becoming an essential part of software development and security. Code signing is not a new technology, and as code signing-related incidents increase, the difficulty of getting it right increases as well. In the simplest terms, code signing is the process of digitally signing executables and scripts to confirm the software author and guarantee that the code has not been altered or corrupted since it was signed. It provides a level of security and trust critical in the digital age. With a surge of high-profile hacker attacks on IT infrastructure globally, technology executives are tasked with ensuring their organizations are secure and ask themselves, “Do I really have my code signing practices under control?”

We’ve collaborated with code signing experts, SignPath, which provides automated, repeatable and secure code signing processes as-a-service and self-hosted, to break down code signing and how organizations can strengthen software security. Below are key takeaways to guide you through unlocking the power of code signing:

  1. Critical Security Practice: Code signing is essential in verifying software authenticity and ensuring that code has not been compromised, reinforcing its necessity as cyber threats continue to rise.
  2. Strengthening Trust: By validating software origins through digital signatures, code signing enhances user confidence and complies with stringent industry regulations.
  3. Adapting to Change: The practice is rapidly evolving with technology, embracing automated processes and the integration of AI to meet the security demands of the Internet of Things (IoT) era.
  4. Protecting Software Supply Chains: Code signing is key to securing software supply chains, preventing unauthorized alterations and maintaining the integrity of software across multiple distribution stages.
  5. Future-Proofing Software: As threats grow in sophistication, code signing is advancing towards automation and more robust security measures to safeguard the integrity of software supply chains and stay ahead of future challenges.

Understanding Code Signing  

understanding code signing

Code signing is a critical component of software security that guarantees the integrity and authenticity of the software delivered to the end-user. At its most basic level, code signing is the process of digitally signing executables and scripts to verify the software author and ensure that it has not been altered or corrupted since it was signed.  

The mechanics of code signing begin with the developer or software publisher, who uses a private key to sign their software digitally. This involves creating a hash of the software and then encrypting this hash using the private key. This produces a digital signature, which is then appended to the software and certificate.  

Code signing is a critical process in software development, ensuring the integrity and authenticity of software by allowing end users to verify the developer or publisher. To protect critical cryptographic keys from theft, and to control the provisioning of code signing certificates, organizations often use dedicated code signing services. Traditionally, these services have used a hash-based approach: a pre-computed hash digest of the software's code is sent to the code signing service, resulting in a signature using the private key. While this method is simple to implement, it leaves implementation complexity and deeper security concerns with development teams.

Recent years have seen increasing demand for file-based signing, a method that is rapidly gaining prominence for its enhanced security features. Unlike hash-based signing, which primarily focuses on proper key protection, file-based signing takes a more comprehensive approach. It allows the code signing service to inspect the software itself and sign its individual files and modules in a single step, eliminating several attack vectors and enforcing policies at the same time.

Another important concern is ensuring the integrity of the software from its origin. Ideally, the signing process is tied to policy-based verifications of the software development process. That ensures that the signature provides a clear trace back to the software pipeline and the policies present at creation of the software. A well-designed code signing pipeline thus addresses potential weaknesses in the hash-based method, where the primary concern is key protection, without any policy control over the software itself or the process used to create it.

Critical elements in the code signing process are digital certificates and private keys. The digital certificate, issued by a trusted Certificate Authority (CA), contains the public key corresponding to the signer’s private key and certifies the signer’s identity. When the software is installed or run, the recipient's system uses the public key in the digital certificate to verify the digital signature, re-computes the hash of the downloaded software, and compares it to the decrypted hash. If they match, it verifies that the software has not been tampered with and comes from the claimed source, validating the certificate.  

As mentioned above, private keys are used to create the digital signature and must be kept secret and secure. Someone else could sign software in the original developer's name if the private key is compromised. Certificate Authorities (CAs), the trusted entities in the ecosystem, are responsible for verifying the identity of the entities to which they issue certificates. The role of CAs in the code signing process is crucial as they establish the trustworthiness of the software by vouching for the software publisher’s identity.  

Benefits of Code Signing  

Code signing offers several benefits, all centered around enhancing software security and instilling user confidence. One of the primary advantages of code signing is its role in improving trust in software security. When software is signed, users can verify the identity of the software author and confirm that the software hasn't been altered since it was signed. This gives users the assurance that the software they are downloading is secure and comes from a verified source.  

The integrity of software is paramount, and code signing plays a critical role in protecting it. Creating a digital fingerprint of the software at the time of signing can detect any alterations or tampering with the software after it is signed. This ensures that users receive the software exactly as the developer intended, free from any unauthorized modifications or harmful code.  

Additionally, code signing enhances user confidence and bolsters the reputation of software. Verifying the software’s source and ensuring its integrity makes users more likely to trust and download it. This increases the software’s reputation, particularly when compared to unsigned software that triggers warning messages upon installation.  

Finally, code signing facilitates compliance with regulatory requirements. Many industries have strict software development and distribution regulations, including the necessity for digital signatures on code. By signing code, businesses can ensure they comply with these regulations, avoiding potential fines and reputational damage. It could lead to misunderstandings if no distinction is made between software designed for general users and software meant for internal use. For example, users are often asked to agree to terms and conditions with Windows.  

Benefits of code signing

Latest Trends in Code Signing  

In cybersecurity, code signing continues to evolve, adapting to modern challenges and embracing the benefits of innovative technologies. Modern code signing methods have been progressing rapidly, shifting towards methods such as automated processes and hardware-backed keys. The need for secure, trustworthy software applications immune to unauthorized modifications drives this evolution.

In the Internet of Things (IoT) era, the importance of code signing has been magnified. As billions of connected devices exchange data, ensuring the integrity and security of this vast array of software becomes critical. Thus, code signing has become an integral part of IoT, securing software updates, confirming the authenticity of applications, and protecting against the infiltration of rogue codes.  

These are exciting times in the world of code signing, as these latest trends signify a robust response to the escalating threats in the cybersecurity landscape. The importance of secure, reliable, and advanced code-signing methodologies cannot be overstated as we continue to deepen our reliance on digital technologies.  

The landscape of code signing is rapidly evolving, particularly in light of recent changes spearheaded by the CA/Browser Forum, marking a significant shift in the past five years. These changes, focusing on the introduction of new Code Signing Baseline Requirements (CSBRs), aim to combat the risks associated with compromised code signing certificates, which have been exploited in malware attacks. As a result, the industry is moving towards stricter security measures for the generation and storage of code signing certificate private keys, emphasizing the need for keys to be generated and stored in certified hardware security modules. This development signifies a departure from earlier practices, where key generation in software posed a high risk of private key compromise, and underscores the necessity of adapting to these enhanced security protocols to maintain the integrity and trustworthiness of digital assets.

Within this context, Thales further explains the implications of these new standards and the broader industry trend toward bolstering digital trust infrastructure. These developments are important in setting new benchmarks for code signing security, highlighting the critical role of secure practices in the face of evolving cybersecurity challenges. This shift reflects a proactive approach to ensuring the reliability of code signing practices, which is essential for safeguarding digital transactions and the distribution of software in today’s increasingly digital world.

Challenges and Solutions in Code Signing  

Code signing is not without its challenges. Common issues often revolve around key management, specifically the secure storage and use of private keys. If a private key is lost or compromised, it can lead to significant security threats, including distributing malicious software under the guise of legitimate applications.  

Another frequent challenge involves keeping track of and managing multiple code signing certificates, especially in large organizations. There can be issues related to the expiry of certificates, which can interrupt software delivery if not appropriately handled.  

To overcome these challenges, best practices recommend strict control and management of private keys. Keys should be stored securely, with access limited to only essential personnel. Hardware Security Modules (HSMs) often provide a highly secure environment for key storage and use.  

It is essential to keep track of all code signing certificates precisely, including due dates for renewal, to avoid unexpected termination. Moreover, dual code signing, which permits code signing with SHA-1 and SHA-256 certificates, can help ensure compatibility across diverse systems and platforms.

Automated code signing platforms have started to play an increasingly important role in addressing these challenges. These tools can automate the process of signing code, thus reducing human errors and ensuring consistent application of security policies. They can also help with certificate and key management and provide detailed logs and audit trails, which are particularly useful for compliance and troubleshooting.

The aim should be automation, and there is a current trend towards it. Why is it not the norm yet? This is because secure signing relies on USB tokens when not utilizing a code signing service. People assume that manual signing leads to more thoroughness, but that is now seen as a mistake-prone fallacy.

Use Case: Software Supply Chain Security

Software supply chain security refers to the efforts and measures to protect all aspects of the software supply chain from various threats. The software supply chain encompasses everything from the development environment, source code, libraries, and components used in the software to the processes involved in packaging, distribution, and updating the software. A breach at any point in the software supply chain can lead to severe consequences, including distributing malicious software to end-users, stealing sensitive information, or compromising critical systems.

Code signing plays a crucial role in securing the software supply chain. It adds a layer of trust and validation to the process. When a piece of software is signed, it attaches a digital signature that verifies the identity of the software author or provider and ensures that the software has not been tampered with or altered since it was signed. This process is critical in multi-party software supply chains, where code often passes through various stages and hands before reaching the end user.

If part of the supply chain is compromised and unauthorized changes are made to the software, the digital signature will result in a  failed verification. This acts as an effective deterrent to potential attackers, as any changes they make will be detected. Using code signing certificates issued by trusted Certificate Authorities (cAs) helps establish and maintain trust in the software supply chain. These cAs verify the entity’s identity to which they issue the certificate.

Topic expert Vincent Delmas, Senior Staff Product Security Engineer with more than a decade of experience in dealing with critical cyber security infrastructure in the highly regulated medical device manufacturing industry, provides us with an insider view on the importance of securing the Software Supply Chain. According to Mr. Delmas, securing the software development supply chain is an intricate balancing act between production and operation.  

The most challenging aspect of this endeavor lies in fortifying the supply chain without stifling innovation. It’s a delicate dance where security and agility must coexist. As organizations navigate this dynamic landscape, they must continually adapt and evolve their security practices to meet the ever-changing threat landscape. The security of the software supply chain is not a one-time endeavor but an ongoing commitment that requires vigilance, collaboration, and a forward-looking approach.

In this digital age, where innovation is the lifeblood of progress, striking the right balance between security and innovation is imperative. By embracing robust security measures, fostering a culture of awareness, and implementing best practices throughout the software supply chain, organizations can confidently advance their innovations while safeguarding against cyber threats, ensuring the integrity of their digital products, and maintaining the trust of their customers and stakeholders.

To fortify your organization’s software supply chain effectively, consider several critical practices, including code signing, ensuring malware-free shipping, implementing a software release approval process, and conducting regular audits.

digital software supply chain security

Future of Code Signing  

Looking forward, the future of code signing is intertwined with the evolution of technology and the escalating complexity of cybersecurity threats. We predict several trends and developments that could shape the code signing landscape. Among them, automation will continue to gain prominence, with more organizations adopting automated code signing tools to improve efficiency, reduce human error, and ensure consistent application of security policies.  

Code signing will also become an increasingly integral part of comprehensive cybersecurity strategies. As software supply chains become more complex and cyber threats more sophisticated, organizations will recognize the importance of validating the integrity and authenticity of software. This will lead to a greater emphasis on secure key management and the adoption of advanced methods like dual signing and hardware-backed keys.  

Quantum computing, with its potential for enormous computational power, presents both a challenge and an opportunity for code signing. On the one hand, quantum computers could break current cryptographic algorithms used in code signing, necessitating a shift towards quantum-resistant algorithms. However, code signing could also protect against quantum computing, providing security against future threats.

The specifics of these trends and the speed at which they progress will depend on various factors, including technological advancements, changes in the threat landscape, and regulatory developments. Regardless of the exact path the future takes, it’s clear that code signing will continue to play a crucial role in software security, adapting and evolving to meet new challenges and needs.  

Conclusion: Unlocking the Power of Code Signing  

In conclusion, code signing is a cornerstone of modern cybersecurity, critical in ensuring software integrity, enhancing user trust, and securing the software supply chain. As technology advances, we foresee an evolving landscape where automated processes, AI, blockchain, and even quantum computing shape the future of code signing. Adopting innovative solutions like SignPath and a comprehensive understanding of code signing’s role will empower organizations to navigate these complexities. As we continue to deepen our reliance on digital technologies, securing our digital world remains paramount, and the significance of advanced and reliable code-signing methodologies cannot be overstated.

With a deep focus on cutting-edge research and development in technology and cybersecurity, we are uniquely positioned to enhance your understanding and implementation of secure code signing practices. Reach out to our team today to secure a competitive edge in digital security and uphold the highest standards of software integrity through our comprehensive research capabilities.