Code Signing Certificate
In the software industry, building trust with users is crucial for the success of any application or executable program. Users need assurance that the software they are installing is genuine, safe to use, and free from malware. This is where code signing certificates come into play.
A code signing certificate is an essential tool used to digitally sign executable files like .exe, .msi, .dll, drivers, scripts, and other software components. The certificate validates the identity of the publisher and integrity of the code. This comprehensive guide will provide an in-depth understanding of what code signing certificates are, their benefits, types, working process, use cases and everything else you need to know.
What is Code Signing Certificate?
A code signing certificate is a digital certificate issued by a Certificate Authority (CA) that allows developers and software publishers to digitally sign their software and executable files. The signature confirms that the code is original and has not been altered or corrupted since it was signed by the software publisher.
The purpose of a code signing certificate is to establish trust and ensure that the software comes from a genuine source. The certificate utilizes public key cryptography to validate the authenticity and integrity of the software code.
When the code is digitally signed using the code signing certificate, the software binds the signature to the executable file. The signature contains information about the publisher’s identity and a hash of the file encrypted with the private key.
Later, when the user tries to install the software, the signature is verified using the public key. If the signature is valid and the hash values match, the software can be trusted. The digital signature protects the software from tampering and proves it comes from the trusted publisher.
Why are Code Signing Certificates Important?
There are several key benefits of using a code signing certificate for software publishers:
1. Builds Trust and Credibility
Code signing certificates help establish trust and credibility for software publishers. It provides the identity reassurance users need before downloading and installing applications on their systems. The verified digital signature conveys to users that the software is genuine and safe to use.
2. Removes Warning Messages
Unsigned executable files often trigger scary warning messages like “Unknown Publisher Security Warning” during installation. This freaks out users and results in aborted installations. Code signing eliminates these warnings by proving the authenticity of the publisher.
3. Protects Integrity of Code
The cryptographic signature protects the integrity of the code and ensures it has not been altered after signing. Users can be confident they are installing the original software file published by the developer.
4. Confirms Authenticity of Publisher
Code signing certificates confirm the authenticity of the software publisher through stringent verification processes. Users can be assured that the software is coming from the genuine publisher and not an impersonator.
5. Boosts Conversion Rates
By establishing trust and eliminating warnings, code signing certificates lead to increased install rates and software adoption. More users are willing to download and use software that is digitally signed.
6. Compliance with Industry Regulations
Code signing provides compliance with software industry regulations that mandate authentication of software publishers. For example, Microsoft requires drivers to be digitally signed.
Types of Code Signing Certificates
There are three main types of code signing certificates provided by Certificate Authorities:
1. Organization Validated (OV) Code Signing
OV code signing certificates validate the identity of the organization through basic verification processes. They confirm that the business who developed the software legally exists.
The validation steps include confirming the organization’s legal name, physical address, and ownership of the registered domain name. Email and phone verification are also performed.
OV certificates offer a base level of security and are suitable for signing software for internal organizational use. They help identify the software publisher to users within the organization.
2. Extended Validation (EV) Code Signing
EV code signing certificates involve thorough verification of the organization’s legal, operational and physical existence. The rigorous validation requirements ensure that the organization’s identity is genuine.
They check business registration documents, confirm physical office location, verify executives’ identities, and assess the organization’s continuity of operations.
EV code signing certificates enable the signed code to establish an instant reputation with Microsoft SmartScreen filters. This provides the highest level of user trust and confidence in the software.
3. Individual Code Signing
Individual code signing certificates are used by independent software developers and technology enthusiasts for signing software or apps they have built.
It verifies the identity of the developer through legal documents such as passports, government IDs, driver’s license, etc.
This allows independent creators and hobbyists to sign their executables and gain credibility even if they are not a registered business. It establishes trust for user-developed code and self-published programs.
How Does a Code Signing Certificate Work?
Here is an overview of how code signing certificates digitally sign software files and validate their authenticity:
Digital Signature Attached to Executable
The code signing process starts with the software developer or publisher generating a certificate signing request (CSR) and submitting it to a Certificate Authority. The CSR contains information that will be included in the digital certificate like the publisher name, public key, and other details.
The CA then issues the code signing certificate after validating the requestor’s identity. The certificate issued contains the software publisher’s details bound to a public-private key pair.
The private key remains securely stored in a cryptographic token or hardware security module (HSM) under the publisher’s control.
The developer uses the private key to generate a unique digital signature for the software executable. This signature binds the executable to the publisher’s identity contained in the certificate.
Signature Verification using Public Key
When a user downloads the digitally signed software, the signature is verified using the public key embedded in the code signing certificate.
The verification process validates that the private key used to sign the executable matches the public key in the certificate. This proves the software is legitimately signed.
The signature also contains a cryptographic hash of the executable file which is recomputed and matched against the original hash to confirm the code has not changed.
If the public and private keys correspond and the hash values are identical, the publisher’s identity is authenticated and the integrity of the code is validated.
User Trust in Authentic Software
By successfully verifying the code signing certificate, the user can trust that:
- The software is published and digitally signed by the genuine developer or company
- The code has not been altered or tampered with since it was signed
- The executable file is authentic and safe to install and use on their device
This entire public key infrastructure (PKI) process enables trusted third-party validation and authentication for software files and publishers. Users can have confidence in installing and running digitally signed programs on their computers.
Code Signing Certificate Workflow: Step-by-Step
Here is a step-by-step overview of the typical code signing certificate workflow:
1. CSR Creation
The first step is to generate a certificate signing request (CSR) on the workstation where the code will be signed. The CSR contains important information such as the applicant name, public key, algorithms used, and so on.
When generating the CSR, the subscriber has to specify details like certificate type (OV, EV or individual code signing) validity period, signature hash algorithm, and key size.
2. Identity Verification
The Certificate Authority will verify the identity of the publisher based on the type of code signing certificate purchased.
For OV certificates, basic business identity checks are done. EV certificates require thorough organizational vetting. For individual developer certificates, the person’s identity is validated.
3. Certificate Issuance
After the CA successfully validates the applicant, they will issue the code signing certificate containing the publisher details bound to the public key. This certificate is valid for 1-3 years based on the chosen validity period.
4. Download and Install Certificate
Once issued, the subscriber can download the code signing certificate from their CA account and install it on their signing workstation using the tool provided by the CA or Microsoft CertMgr. This installs the certificate containing the public key and publisher identity onto the local machine.
5. Sign Executable Files
Now the private key associated with the certificate can be used to digitally sign executable files like .exe, .msi, .ocx, .dll, .ps1, and so on. Signing is typically done using Microsoft SignTool or MS Visual Studio.
6. Redistribute Signed Software
The final step is to distribute the software executables signed using the code signing certificate. This can be done using the company website, app store, CDN or third-party download sites. The certificate ensures users can trust the publisher when they install the signed software.
Implementing Code Signing in Development
When it comes to the development of software, the integration of code signing is a critical step in the process. It’s not just about slapping a signature on the code at the end of the development cycle; it’s about making code signing an integral part of the continuous integration and delivery pipeline. Implementing code signing correctly can protect the integrity of your software and ensure the security of your end-users.
Understanding the Role of Code Signing in Development
Code signing serves multiple purposes in the development process:
- Security: It ensures that the code has not been tampered with since it was signed.
- Authenticity: It certifies that the code comes from a known, trusted source.
- Compliance: It often meets legal or regulatory requirements for software distribution.
Integrating Code Signing into the Software Development Lifecycle
The Software Development Life Cycle (SDLC) consists of several stages, from planning and writing code to testing and deployment. Here’s how code signing fits into each stage:
- Planning: Determine the code signing requirements for your project. Decide who will be responsible for signing the code and managing the keys.
- Development: Developers write code in a secure environment. Access to signing keys should be restricted and monitored.
- Build: When the code is compiled, it should be signed immediately to protect the build artifacts before they are distributed for testing.
- Testing: Signed code is tested. If the code changes, it needs to be re-signed, ensuring that testing is done on the exact version that will be released.
- Release: Final versions are signed with a production key that differs from the development/testing key.
- Maintenance: Keep signing keys secure and audit their use regularly. Update and revoke keys as personnel changes occur or in response to security incidents.
Automation Tools for Code Signing
To maintain efficiency and reduce the risk of human error, automating the code signing process is vital. Automation tools can help in several ways:
- Enforce Signing Policies: Tools can prevent unsigned code from moving through the development pipeline.
- Integrate with Build Servers: Tools like Jenkins, TeamCity, or Travis CI can execute code signing as part of the build process.
- Manage Keys and Certificates: They can store keys securely and use them to sign code without exposing them to users.
Secure Storage of Private Keys
Securing the private keys used for code signing is of paramount importance. If these keys fall into the wrong hands, the integrity of the software and the trust of the users are at risk. Here are the ways to ensure the private keys are stored securely:
Hardware Security Modules (HSMs):
Hardware Security Modules (HSMs) are specialized, tamper-resistant hardware devices designed to manage digital keys securely. They provide a secure environment for key generation, management, and use. Code Signing HSMs are certified to meet rigorous security standards, such as FIPS 140-2, which is a requirement for many government and enterprise applications. By storing keys in an HSM, you ensure that they are never exposed to the internet or stored on a less secure system where they could be compromised.
External Physical Devices (Tokens, YubiKey, etc.)
External physical devices such as cryptographic YubiKey tokens or products like YubiKey serve as portable HSMs, providing strong two-factor authentication and secure key storage. These devices are plugged into a computer only when needed, thereby limiting exposure to potential attacks. They are particularly useful for individuals or small teams where dedicated HSMs may not be feasible due to cost or complexity.
Code Signing Enables Secure Software Distribution Across Industries
Code signing is used across many different industries for diverse code and software distribution scenarios:
- Driver and application signing: Windows and macOS require drivers/apps distributed outside stores to be signed by a trusted publisher certificate. This ensures only legitimate drivers are installed.
- Firmware signing: Device manufacturers sign all firmware updates and packages to guarantee only authorized versions are flashed. IoT devices also increasingly mandate signature verification.
- Mobile app signing: Both iOS and Android app stores verify the signing certificate of all submitted apps before allowing distribution. It guarantees app integrity and the developer’s identity.
- Internal software distribution: Many companies sign internally distributed installers, scripts and software packages to managed systems. Signatures allow verification of authorized updates even without online checks.
- Software repository packages: Open-source project repositories like npm, PyPI, RubyGems etc require developers to sign packages with GPG/PGP keys for integrity and attribution.
- Secure OTA updates: Cars, medical devices and other ‘always on’ systems depend on code signatures to trustlessly establish the authenticity of over-the-air firmware and patch payloads.
- Build integrity and CD pipelines: Build servers producing automated packages as part of continuous delivery can sign artifacts at release time using the organization’s Code Signing Certificate to guarantee integrity from commit to deploy.
The specifics of code signing implementation may differ based on the code type, distribution method, and targeted platforms but the core goal of authenticating identity and verifying integrity remains the same across use cases.
Should You Get a Code Signing Certificate?
Here are some key considerations when evaluating if your software needs code signing:
- Do you want to maximize user trust by proving the authenticity of your software?
- Is it important to eliminate scary warning messages that hinder software adoption?
- Do you distribute software through public channels and worry about tampering?
- Does the platform or ecosystem require mandatory code signing?
- Do you want to comply with industry best practices for secure software distribution?