What is the Certificate Chain of Trust? Everything You Need to Know

Certificate Chain of Trust is the digital equivalent of a government-issued ID system, with layers of security, providing layered security for online transactions. At its core is Public Key Infrastructure (PKI), which enables the cryptographic operations that authenticate and validate digital certificates. This layered security framework helps protect everything from your online banking sessions to your private messages.

In this blog, let us understand the certificate chain of trust and how it deals with multiple digital certificates.

What is a Certificate Chain of Trust?

A certificate chain of trust is a series of certificates in the hierarchy of digital certificates. The chain begins with the end-entity certificate (also known as the leaf certificate), following intermediate certificates, and root certificates as the apex in the hierarchy.

A TLS/SSL certificate and its connection to a reliable certificate authority are collectively referred to as the certificate chain of trust. This certificate is considered reliable when it can be traced back to a trusted root certificate authority (root CA).

In a certificate chain of trust, each certificate is signed by the entity specified by the next certifier in the chain; starting from the server certificate, through intermediate certificates, and finally in the root certificate.

The primary goal of the chain of trust certification is to demonstrate that a specific certificate comes from a reliable source. So, the user knows while establishing a connection that the website is secure if the certificate is authentic and is chained to a root CA in the trust store of the client browser.

Example of Digital Certificate Chain of Trust

Let’s understand a common scenario in our day-to-day lives.

When you visit your bank’s website, type the web address, and hit “Enter,” your browser starts connecting to the bank’s server.

The browser checks the server’s digital certificate’s details, including the issuer, expiration date, and digital signature. Next, it identifies the issuer (Intermediate Certificate Authority) and verifies its validity by checking the signature and issuer.

The browser continues going up to the chain until it reaches the trusted root certificate, which is already pre-installed in its certificate store. The browser checks that no certificates are expired, revoked, or tampered with and that the website domain matches the certificate details.

If everything is good to go, the browser trusts the certificate and establishes a secure connection. Otherwise, it will show a security warning or block access to the website.

Components of Certificate Chain of Trust

As shown in the image, a certificate chain of trust consists of three primary certificates:

• Root CA
• Intermediate CA
• Server CA or End Entity CA

Let’s learn each of these components in detail.

1. Root Certificate

   A root certificate is a self-signed certificate created by a trusted Certificate Authority (CA), representing the highest level of trust in a Public Key Infrastructure (PKI). It is at the apex of the certificate hierarchy in a multi-level chain of trust. Adhering to the X.509 certificate standards, a root certificate is a self-signed certificate. Web clients and applications can confirm that a reliable source, i.e. the root CA, has verified the identity of the end entity.

   While the root CA rarely signs end-entity certificates directly, it closely monitors the private key. If the private key of the root CA (the Trust Anchor) is compromised, it affects all certificates issued by that CA, including those signed with that private key. In such cases, all intermediate CAs and end-entity certificates in the chain will need to be reissued.

   To issue certificates, the root authority designates and certifies to one or more intermediate CAs and chains them to the root CA.

2. Intermediate Certificate

   Root CA issues the intermediate certificate which acts as a bridge between the root certificate and end-entity certificates. There can be multiple intermediate levels or intermediaries.

   An SSL certificate chain will nearly always contain at least one intermediary certificate. They offer a crucial connection that allows the Root CA to broaden its reliable reputation to end-entities that otherwise lack it.

   By improving security and decentralizing trust, the intermediate CA shields the root CA from harm. It uses its private key to sign certificates, and the intermediate certificate’s public key can be used to confirm this. Through the intermediate certificate authority, this signature creates a chain of trust that runs from the root CA to the server.

   Even in case the private key of the intermediate CA is compromised due to the structure, the security of the entire chain will still be intact. The breach will be limited to the intermediate level and will not impact the root certificates.

3. Server or End Entity Certificate

   The server or end-entity certificate is issued to a specific entity (like website, organization, or server) based on the certificate request. It represents the final destination in the certificate chain of trust and contains specific details about the certificate holder.

   We arrive at the server SSL certificate after descending the chain of trust from the Intermediate CA. It is the last and most noticeable link in the certificate chain of trust. When you access a secure website, your browser verifies this digital credential, which is granted to the website owner. It guarantees that you are not connecting to a fraudulent website by proving the identity of the server.

   The Secure Sockets Layer (SSL) certificate completes the chain of trust by linking the server’s certificate to the root CA through the intermediate CA. It includes the public key of the server as well as information about the company that owns it.

   Server certificates enable secure and encrypted communication between your browser and server. These certificates protect sensitive information like credit card details, personal details, and other sensitive information from malicious or threat actors.

   Read Also: Root Certificates vs. Intermediate Certificates

How Does a Certificate Chain of Trust Work?

While installing SSL certificates, you receive an intermediate root certificate or bundle. Once your website’s SSL certificate is installed, a browser begins the process of chaining it back to a trusted root. It will start by following the chain to the installed intermediate, after which it will keep going until it reaches a trusted root certificate.

To get a branded SSL Certificate, you must verify that it is issued by a reliable certificate authority (CA). The certificate will be trusted if it is legitimate and can be linked to a reliable root. The browser will alert the user about the certificate if it cannot be chained to a trustworthy root. This is how the SSL certificate trust chain works.

We can sum up the process as –

Verification > Validation > Trust Establishing > Checking for Expiry or Revocation

1. Verification of the certificate.
2. Validation of the certificate and identity for security.
3. Establish trust by verifying that the certificate comes from an authentic authority like root CA.
4. Lastly, check whether the requested certificate is yet valid and not expired or revoked. A request for an expired or revoked certificate might be alarming as it may suggest a forgery or scam.

The figure given below shows the SSL chain and the details of the signing authorities.

The Role of Certificate Authorities (CAs) in Certificate Chaining

Certificate Authority (CAs) are reliable third parties issuing digital certificates, such as SSL, code signing, and other digital security certificates. They deal with public keys and other credentials pertaining to encryption.

CAs use cryptographic keys to authenticate and link websites, email addresses, companies, and other entities. The CA is in charge of confirming and providing unique certificates for the organization’s data. Before awarding the certificate, the CA confirms the applicant’s information with the Qualified Information Source (QIS).

The root certificate authority (Root CA) is a trusted organization at the top of the certificate hierarchy. Digital certificates are issued to intermediate certificate authority by the root CA. Between the root CA and the end entities (such as websites or organizations), intermediate CAs serve as a bridge.

The Root CA authorizes intermediary CAs, these intermediary CAs issue certificates and verify the legitimacy of the organizations they certify. By doing this, they create confidence in the certificate chain and attest to the entity’s legitimacy. To guarantee the integrity and reliability of the certificates they issue, CAs are required to adhere to stringent policies and security procedures.

They undergo audits and regulations to uphold the greatest security and trust standards. In the certificate chain of trust, Certificate Authorities (CAs) are the most essential entity.

Importance of Maintaining the Chain of Trust

Any online communication involving your personal information, such as passwords or credit card numbers, must be secure. The certificate chain of trust becomes crucial at this point.

The certificate chain of trust helps you verify that the website you are currently on is legitimate. This is why the process involves checking for certificate revocation status, including the certificate revocation list (CRL) and other methods like OCSP. You would be exposed to man-in-the-middle attacks without this authentication, in which an untrusted third party may intercept and abuse your data.

Additionally, the certificate chain of trust protects companies’ online reputations. Web browsers will alert visitors to security issues if a website does not employ a valid SSL certificate. Such issues have the potential to turn off potential clients and harm the business’s image.

Essentially, the SSL chain of trust is the foundation of the entire digital space’s data security structure. It guarantees integrity and protects privacy.

Some Common Troubleshooting of Chain of Trust Issues

These are some common issues of the digital certificate chain of trust you might face. You can easily troubleshoot them by

1. Configuring the server correctly

   Installing your TLS certificate and related intermediates is only one step in the procedure. Setting up your server properly to work with the certificate is equally important. Setting up a server correctly is very important.

2. Verification of CAs

   Verify that a reputable Certificate Authority (CA) has issued your TLS certificate. Web browsers won’t believe your TLS certificate if it hasn’t. If you have self-signed your certificate, this is also a cause for concern.

3. Correct Installation of Intermediate Certificate

   Make sure the intermediate certificates are installed correctly. Accurate installation of intermediate certificates is essential. It is not a good idea to rely just on chance, even though some browsers might try to close gaps in the certificate chain. When configuring your TLS certificate, be sure that all intermediate certificates are installed successfully.

Best Practices for Certificate Chain of Trust

A few best practices that can ensure a trustworthy certificate chain of trust are –

1. Updating and rotating the certificates regularly. It helps to secure them against malicious activities.
2. Choosing reputable Certificate Authorities makes the certificates more reliable.
3. Implement robust certificate management processes.
4. Monitor certificate expiration dates to avoid forgery or scams.
5. Use automation tools for certificate tracking.

How the Certificate Chain of Trust Enhances SSL/TLS Security

SSL/TLS certificates are at the heart of secure online communication. The certificate chain of trust enhances SSL/TLS security by establishing that the server’s certificate is valid and issued by a trusted authority. It ensures that the communication between a client (e.g., a browser) and the server is secure, and that the identity of the server is verified before any sensitive data is exchanged.

This trusted path prevents man-in-the-middle attacks and other types of cyber threats that could otherwise exploit untrusted certificates.

Conclusion

Data integrity, impersonation prevention, and online communication security all depend on the certificate chain of trust. Using visual cues in web browsers to show how reliable websites and services are, it also increases user trust.