What is a Code Signing Certificate?

A code signing certificate is a type of digital certificate used by software developers to sign applications, drivers, executables, and software programs. It serves two primary purposes:

1. It verifies the authenticity of the software publisher, confirming that the code comes from a known and trusted source.

2. It ensures that the code hasn’t been tampered with or altered since it was signed.

At its core, a code signing certificate is composed of several key elements:

• A public key, which is openly shared and used to verify the signature.

• A private key, kept secure by the developer and used to create the digital signature.

• The digital signature itself, which is attached to the software.

• Information about the certificate owner, including the organization name for organizational certificates.

When a developer signs their code with a code signing certificate, they’re essentially providing a digital stamp of approval. This stamp tells users, “This software comes from me, and it hasn’t been altered since I created it.”

How Code Signing Certificates Work

To understand how code signing certificates work, let’s break down the process step by step:

1. Obtaining the Certificate: The process begins when a developer or organization obtains a code signing certificate from a trusted Certificate Authority (CA) such as SSL.com. This involves verifying the identity of the certificate applicant to ensure they are who they claim to be.

2. Signing the Code: Once the developer has the certificate, they use the private key associated with it to create a cryptographic hash of their software. This hash is then encrypted with the private key to create the digital signature.

3. Attaching the Signature: The digital signature, along with the developer’s public key (contained in the certificate), is attached to the software.

4. Distribution: The signed software is then distributed to users through various channels, such as websites, app stores, or enterprise software distribution systems.

5. Verification: When a user downloads and attempts to run the software, their operating system uses the public key provided with the software to decrypt the digital signature. It then creates a new hash of the software and compares it to the decrypted hash from the signature.

6. Confirmation: If the two hashes match, it confirms that the software hasn’t been altered since it was signed. The operating system also checks that the certificate used for signing is from a trusted CA and hasn’t expired or been revoked.

This process relies on asymmetric cryptography, where the private key used for signing can only be decrypted by the corresponding public key. This ensures that only the genuine owner of the certificate can create valid signatures for their software.

Benefits of Code Signing Certificates

Code signing certificates offer numerous benefits for both software publishers and users:

Security:

• Protection against tampering: Signed code allows users to verify that the software hasn’t been altered since it was signed, protecting against malware insertion.

• Malware prevention: Code signing helps prevent the spread of malware by ensuring that code comes from a known, verified source.

Trust:

• Increased user confidence: Users can trust that the software comes from a legitimate source and hasn’t been compromised.

• Reduced security warnings: Properly signed software often bypasses security warnings that unsigned software triggers, leading to a smoother user experience.

Reputation:

• Brand protection: Code signing helps protect a company’s brand by preventing others from distributing malicious software under their name.

• Improved credibility: Signed software demonstrates a commitment to security, enhancing the developer’s or company’s reputation.

Compliance:

• Meeting industry standards: Many industries require code signing as part of their security standards.

• Regulatory requirements: Some regulations, particularly in sectors like finance and healthcare, mandate the use of code signing for software distribution.

Integrity:

• Version control: Code signing can help in managing different versions of software, ensuring users have the latest, authorized version.

• Tamper evidence: If signed code is altered, the digital signature becomes invalid, immediately alerting users to potential tampering.

Types of Code Signing Certificates

There are several types of code signing certificates available, each suited to different needs:

Individual Code Signing Certificates:

• Issued to individual developers or small teams.
• Validate the identity of an individual rather than an organization.
• Suitable for independent developers or small projects.

Organization Code Signing Certificates:

• Issued to companies or organizations.
• Display the organization’s name in security dialogs, adding credibility.
• Ideal for businesses distributing software commercially.

Extended Validation (EV) Code Signing Certificates:

• Provide the highest level of authentication and security.
• Require a more rigorous vetting process for the certificate applicant.
• Offer instant reputation with Microsoft SmartScreen Filter, reducing warning messages for users.
• Mandatory for kernel-mode drivers on newer Windows systems.

Time Stamping Certificates:

• Used in conjunction with code signing certificates.
• Allow signed code to remain valid even after the original code signing certificate expires.

Each type of certificate has its own advantages and use cases. The choice depends on factors such as the size of your organization, the type of software you’re distributing, and your target audience.

How to Obtain a Code Signing Certificate

Obtaining a code signing certificate involves several steps:

1. Choose a reputable Certificate Authority (CA): Select a well-known, trusted CA like SSL.com.

2. Determine the type of certificate you need: Based on your organization’s size and needs, choose between individual, organizational, or EV certificates.

3. Generate a Certificate Signing Request (CSR): This process creates a private key on your system and a CSR file to send to the CA.

4. Submit your application: Provide the necessary information and documentation to the CA. This typically includes:

   • For individual certificates: Government-issued ID, proof of address

   • For organizational certificates: Business registration documents, proof of right to use the company name

   • For EV certificates: Additional documentation to prove business operations and identity

5. Verification process: The CA will verify the information provided. This can take anywhere from a few hours for basic certificates to several days for EV certificates.

6. Receive and install the certificate: Once approved, you’ll receive your certificate. Install it on the system where you’ll be signing your code.

7. Secure your private key: Ensure the private key associated with your certificate is stored securely, preferably in a hardware security module (HSM) or YubiKey.

How can I order and install a code signing certificate from SSL.com?

Please refer to the following how-tos for information on ordering, installing, and getting started with code signing and EV code signing certificates from SSL.com:

• Ordering and Retrieving Code Signing Certificates

• How to Install OV Code Signing Certificates

• Using Your Code Signing Certificate

• Getting Started with Your EV Code Signing Certificate

Use Cases and Real-World Examples

Code signing certificates are used across various industries and for different types of software:

• Operating System Components: Microsoft uses code signing for Windows updates and drivers.
• Browser Extensions: Google requires Chrome extensions to be signed before distribution.
• Mobile Applications: Both Apple (iOS) and Google (Android) require signed apps for their stores.
• Enterprise Software Distribution: Large corporations use code signing for approved software installation.
• Internet of Things (IoT): Manufacturers secure firmware updates with code signing.
• Financial Services: Banks use code signing for online banking software and apps.
• Healthcare Software: Medical device manufacturers comply with FDA regulations through code signing.

Common Issues and Troubleshooting

While code signing is generally straightforward, you may encounter some issues:

Expired Certificates:

• Issue: The code signing certificate has expired.
• Solution: Renew your certificate and re-sign the code. Use timestamping to avoid this issue in the future.

Revoked Certificates:

• Issue: The certificate has been revoked, possibly due to a compromise.
• Solution: Obtain a new certificate and re-sign all affected code.

Timestamp Errors:

• Issue: The timestamp server is unavailable or the timestamp is invalid.
• Solution: Try a different timestamp server or check your internet connection.

Certificate Chain Issues:

• Issue: The certificate chain is incomplete or contains an untrusted root.
• Solution: Ensure the entire certificate chain is included when signing, and that your root certificate is from a trusted CA.

Key Compromise:

• Issue: Your private key has been compromised.
• Solution: Immediately contact your CA to revoke the certificate, obtain a new one, and re-sign all code.

Best Practices for Code Signing

To maintain the security and integrity of your code signing process:

• Secure Key Storage: Use hardware security modules (HSMs) or YubiKeys to store private keys.
• Regular Certificate Renewal: Set up reminders to renew certificates before they expire.
• Use Trusted Timestamping: Always timestamp your signatures to ensure long-term validity.
• Implement a Clear Key Management Strategy: Define processes for key generation, storage, use, and destruction.
• Keep Software Updated: Ensure your code signing tools and related software are always up-to-date.
• Separate Signing Environment: Use a dedicated, secure machine for code signing, isolated from daily-use computers.
• Multiple Certificates: Use different certificates for different products or environments (e.g., testing vs. production).
• Regular Security Audits: Conduct regular audits of your code signing processes and infrastructure.

Conclusion

Code signing certificates are essential for maintaining software security and integrity. They verify developer identity and ensure software authenticity, benefiting both individual developers and large corporations across various applications. As cyber threats evolve, the importance of code signing grows.