What Is a CA Bundle? How to Create & Install It for SSL Security

Understand the CA Bundle in SSL Hierarchy, Including the Download, Creation, and Configuration Process

SSL certificates use PKI (Public Key Infrastructure) to form a chain of trust for secure HTTPS connection between server and client. However, to be fully trusted by browsers and applications, SSL certificates must be validated. That is when the CA Bundle comes into picture.

CA Bundle is a collection of intermediate and root certificates that link your SSL certificate to a trusted Certificate Authority (CA). Without it, browsers do not recognize your certificate as valid, resulting in security warnings and potential disruptions for users.

Let’s get into detail and understand what is a CA bundle in SSL, why it matters and how can you create it.

What Is a CA Bundle in SSL?

A CA Bundle file is a set of intermediate and root certificates from trusted Certificate Authorities (CAs). It is a type of file required to establish the chain of trust for an SSL/TLS certificate. Upon issuance, an SSL certificate is usually signed by an intermediate certificate. The intermediate cert is linked to a trusted root certificate maintained by a Certificate Authority (CA) such as DigiCert and Sectigo.

At the time of SSL/TLS handshake, the server presents its SSL certificate along with the CA Bundle. The client (e.g., a web browser) uses this bundle to verify the legitimacy of the server’s certificate. It follows the chain from the leaf certificate (your SSL certificate) up to a trusted root certificate. If a certificate in the chain is missing or invalid, the browser will generate a security warning or error message.

Operating systems, web browsers, and devices maintain a certificate trust store, which contains pre-installed root certificates from CAs. When a browser encounters a website using SSL, it checks the CA Bundle with this trust store to confirm the certificate’s authenticity. If the CA Bundle is properly configured, the connection proceeds securely. If not, users see warnings like “Certificate Not Trusted” or “Unable to Verify Certificate Issuer.”

How to Create a CA Bundle for SSL?

Creating a CA Bundle involves combining root and intermediate certificates from trusted CAs into a single file, making it easier and quicker to process. Follow the below steps to manually create a CA Bundle:

Step 1: Get Root and Intermediate Certificates

Start collecting certificates, both root and intermediate, from globally known Certificate Authorities. You can download such certificates from official CA websites, your SSL provider’s dashboard, or trusted repositories like your operating system’s certificate store.

When it comes to security, choose your SSL certificates from respected and trustworthy CAs. Using unverified certificates can risk the security and trust between you and your client.

Step 2: Organizing Certificates in a Directory

Once you gather the necessary certificates, the next step is to list them within a system directory. This simple yet crucial step will simplify the bundling process and reduce errors.

Create a directory (e.g., mkdir ca_bundle on Linux/macOS).
Save each certificate in its original format (.pem or .crt).
Maintain proper file names (e.g., root.pem, intermediate1.pem).

Step 3: Combining Root and Intermediate Certificates

Merge the intermediate and root certificates into a single file using a text editor like Notepad or command-line tools like cat (Linux/macOS) or copy (Windows).

Using a Text Editor:

Open each certificate file in a text editor (e.g., Notepad++, Vim).
Copy the full contents of each certificate, including the header and footer:
```
-----BEGIN CERTIFICATE-----
(certificate data)
-----END CERTIFICATE-----
```
Paste them into a new text file, without any extra spaces or missing lines.

Using the Command Line:

On Linux/macOS:

cat intermediate1.pem intermediate2.pem root.pem > ca-bundle.crt

On Windows (Command Prompt):

copy /b intermediate1.pem + intermediate2.pem + root.pem ca-bundle.crt

Step 4: Arranging Certificates in Sequence

Place the root certificate at the end, preceded by intermediate certificates, creating a clear hierarchy. Incorrect ordering can lead to SSL validation errors. Here’s a CA Bundle file example showing the correct order of certificates:

-----BEGIN CERTIFICATE----- (Intermediate Certificate 1)
-----END CERTIFICATE-----

-----BEGIN CERTIFICATE----- (Intermediate Certificate 2)
-----END CERTIFICATE-----

-----BEGIN CERTIFICATE----- (Root Certificate)
-----END CERTIFICATE-----

Some servers may automatically handle ordering, but structuring the bundle correctly makes all SSL/TLS implementations compatible.

Step 5: Save Files as CA Bundle

Once you import all the root certificates (root keys) and arrange them into a single text file, you’ll need to save the file with a proper name. The CA Bundle file format is typically .pem or .crt, such as “root-certs.pem” or “ca-bundle.crt.”

Step 6: Verifying CA Bundle Integrity

Before starting operations, it is recommended to validate this newly developed CA Certificate Bundle. It will confirm that all certificates are formatted correctly and functional.

Using OpenSSL:

Run the following command to check the certificate chain:

openssl verify - verbose -CAfile ca-bundle.crt your_ssl_certificate.crt

If the chain is valid, you will see an output like:

your_ssl_certificate.crt: OK

If errors occur, check for missing or misordered certificates in the bundle.

Step 7: Deployment of the CA Bundle

Once the CA Bundle is created and verified, you can deploy it wherever the SSL certificates need it—for example, setting up web servers, load balancers, or other network devices wherever the CA Bundle can be specified for the SSL validation process to secure connections.

After deployment, test the configuration to keep the security and system integrity of the SSL connection.

How to Get a CA Bundle for SSL Setup and Integration?

To obtain a CA Bundle one must purchase root certificates that belong to reputed CAs (Certificate Authorities) such as Comodo or others. You’ll be required to go through certain steps, and they’re as below:

Step 1: Download CA Bundle Certificates from CA’s Official Website

Most Certificate Authorities offer CA Bundles through their websites. You can find the CA Bundle file download option in resource section to download the necessary root and intermediate certificate files. Some CAs also provide the CA Bundle with different file extensions, like CRT (Certificate) and PEM (Privacy Enhanced Mail), for compatibility with various server configurations.

Step 2: Use Operating System or Browser Repositories

Modern operating systems and browsers have built-in trusted root certificates, which can form the CA Bundle. It can be accessed through your operating system’s certificate store or even through your browser’s certificate manager that builds the CA Bundles.

On Windows, use the Certificate Manager (certmgr.msc) to access stored root certificates.
On Linux/macOS, check the /etc/ssl/certs/ directory or use OpenSSL commands:
```
openssl x509 -noout -text -in /etc/ssl/certs/ca-certificates.crt
```
Browsers like Chrome and Firefox maintain their own root certificate stores, which get updated regularly.

Step 3: Check Third-Party Repositories

There are few online databases and enterprises that have curated databases of multiple CAs for their root certificates. They provide the CA Bundle to download with directions to get the root certificates from a repository. However, be cautious when using third-party sources – always verify authenticity before integrating certificates.

Step 4: Leverage Automated Certificate Management Systems

There are some cloud platforms and automation tools that manage SSL certificates. For instance, AWS Certificate Manager (ACM), Google Cloud Certificate Manager, and Microsoft Azure Key Vault allow users to add, remove, and manage SSL certificates and their associated CA Bundle certificate authority with little to no human interference.

Step 5: Manually Create the CA Bundle

This option we have learnt step-by-step in the previous section. Manual creation is often preferred for custom SSL deployments requiring specific configurations.

If an automated solution isn’t available, you can roll out your own CA Bundle by concatenating the root certificates you get from trusted sources. You collect the root certificates of various trusted Certificate Authorities and wrap them within a single directory.

What Is the Importance of CA Bundle in SSL Configuration?

CA Bundle is important for establishing safe & trusted communication encrypted with SSL protocol. Here’s why it is essential:

Verifying SSL Certificates

The CA Bundle is essential for issuing SSL certificates that allow a server to provide a verified identity to the client. Whenever a client connects with a secure website, it receives the server’s SSL certificate. The client then checks the signature of the certificate with the CA that’s included within a bundle. This verification method confirms that the server is genuine, preventing attackers from impersonating the server and intercepting communications.
Mitigating Security Risks

If a CA Bundle is not present, clients will face several security risks like MITM (Man-in-The-Middle) attacks, where cyber crooks impersonate client & server and alter their communication. CA Bundles spot fake certificates and mitigate security risks for confidential data that shouldn’t be accessible to any malicious parties.
Building Confidence

When trusted root certificates from reputable CAs are included in the CA Bundle, clients can confirm these SSL channels are trustworthy. The trust in these root certificates is built on the long and rigorous verification of the certificate carried out by the CA, reinforcing user confidence.
Preserving Data Accuracy

SSL with HTTPS security validates the credibility of the servers and works with both data security & safety. The CA Bundles authenticates SSL certificates, which allows organizations to maintain the security of the data transfer process and ensure only authorized parties have access to confidential information.
Meeting Regulatory Requirements

The CA Bundle helps meet encryption protocols and compliances that are needed for data protection policies and industry standards like PCI DSS (Payment Card Industry Security Standard) and GDPR (General Data Protection Regulation). Following such requirements of the different legislation and providing a valid CA certificate is crucial for organizations to avoid potential fines and penalties.

How Do You Combine Your Certificate and CA Bundle?

To enable HTTPS security, a Certificate Authority (CA) bundle is combined with an SSL certificate by appending the contents of the CA bundle file to the SSL certificate file. It can be done by using command-line tools or text editors. The final file will contain both the CA bundle and the SSL certificate. It facilitates client-side verification of the certificate’s authenticity while using the trusted root certificates that already come with the bundle.

The combined file is used for SSL installation on server and client machines to configure the device. However, it’s important to adhere to the installation guidelines provided by the application or server for security and compatibility.

Wrapping Up

For successful HTTPS security and to prevent any unexpected SSL errors, it’s crucial to know the role of CA Bundles in encryption protocols and the setup of the SSL certificates. You can say, CA Bundle is like an extra security layer and trustworthiness, which always comes included whenever you want to install an SSL certificate on your web server.

Here, we’ve covered what is a CA bundle in SSL and how do you create it, along with other details like how to get a CA bundle for yourself if you didn’t get one for yourself. We hope this article proves helpful.

What Is a CA Bundle in SSL? – A Step-by-Step Guide to Create It