What is a Root Certificate? The Backbone of SSL/TLS

Do you ever wonder why you feel confident entering your credit card info on an online store or logging into your bank account? The invisible yet essential defense ensuring your data stays safe is the SSL/TLS certificate infrastructure, and at the top of that security chain is the root certificate. But what is a root certificate, and how does it work? Without it, websites wouldn’t be able to establish trust with users.

This article explores root certificates, explains how they work, and why they’re crucial to protecting online interactions.

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Table of Contents

1. What is a Root Certificate?
2. How Root Certificates Work
3. Importance of Root Certificates in SSL
4. Types of Root Certificates in SSL
5. How Certificate Authorities Manage Root Certificates
6. Potential Risks and Issues with Root Certificates

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What is a Root Certificate?

A root SSL certificate is the highest level of a security certificate in a hierarchy called the certificate chain. It is issued by a trusted Certificate Authority (CA), and this root certificate is used to sign other certificates, such as server or intermediate certificates.

The root certificate is stored securely in trusted repositories, like operating systems or browsers, and it’s rarely issued or installed directly. Instead, it’s used to verify the authenticity of lower-level certificates. If a server’s SSL certificate can trace its validation back to a trusted root certificate, your system knows it can trust that connection.

An example of a root SSL certificate is the DigiCert Global Root G2 certificate, issued by DigiCert, a well-known Certificate Authority (CA). Below is an outline of its contents:

• Subject: C=US, O=DigiCert Inc, OU=www.digicert.com, CN=DigiCert Global Root G2
• Issuer: C=US, O=DigiCert Inc, OU=www.digicert.com, CN=DigiCert Global Root G2. The issuer is the CA that signed the certificate, which in this case is itself, as it’s a root certificate.
• Validity Period: Until January 15, 2038
• Serial Number: 03:3A:F1:E6:A7:11:A9:A0:BB:28:64:B1:1D:09:FA:E5
• Signature Algorithm: sha256RSA
• Fingerprint:CB:3C:CB:B7:60:31:E5:E0:13:8F:8D:D3:9A:23:F9:DE:47:FF:C3:5E:43:C1:14:4C:EA:27:D4:6A:5A:B1:CB:5F

The Subject field shows the entity that owns the certificate. In this case, it’s DigiCert. The issuer is the CA that signed the certificate, which in this case is itself, as it’s a root certificate.

You can also see the hashing and encryption method used to sign the certificate and the fingerprint – a unique identifier for the certificate generated by hashing its contents, used to verify its authenticity.

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How Root Certificates Work

Let’s break down how root certificates establish trust step by step by highlighting the key components:

• Root CA: A root certificate authority creates a root certificate. This certificate is self-signed, which means the same authority both issues and verifies it. Because of this, the root certificate is stored securely, often offline, in hardware security modules (HSMs) to keep it safe.
• Intermediate Certificates: The intermediate CA is a middle layer between the root and end entity certificates (used by websites). It gets its authority from the root certificate and is responsible for signing other certificates.
• End-Entity Certificate (Server Certificate): The certificate a website uses to prove its identity to visitors, allowing your browser to trust that the website is legitimate and that the communication between your browser and the site is secure. The end entity certificate is the one you get from a CA and install on your server, though it wouldn’t exist without the root.
• Chain of Trust: When you visit a site, your browser verifies the certificate chain—starting from the website’s server certificate, moving through intermediate certificates, and finally reaching the root certificate.
• Digital Certificates and Encryption: With the chain verified, encrypted communication can begin. Using Public Key Infrastructure (PKI), the server certificate encrypts the data using a public key, which only the corresponding private key can decrypt.

The chain from the root to the website certificate makes all this possible, ensuring your data is securely transmitted and received. Without this structure, hackers could easily intercept your information, and websites would have no way to prove their legitimacy.

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Importance of Root Certificates in SSL

Now that you understand the mechanics let’s explore why root certificates are important for SSL/TLS and online security.

• Building Trust with Users: SSL certificates play a front role in establishing user trust. When users see the padlock or the HTTPS prefix, they know the site is secure. This trust is anchored in the root certificate. Without it, browsers will flag such websites and warn visitors, preventing them from accessing the web pages.
• Data Integrity: Root certificates maintain data integrity. When data travels between your browser and a website, the SSL certificate encrypts it, preventing third parties from accessing or tampering with it. The root certificate guarantees that encryption starts from a trusted source, validating the entire certificate chain.
• Online Transactions Security: Whether you’re banking, shopping, or just logging into an email account, the security of your information depends on the root certificate. If a root certificate is compromised or expires, it can have disastrous consequences. You wouldn’t want to log into your bank account and get a warning that the site isn’t secure because its root certificate is no longer trusted.
• Website Security: Website security extends beyond just keeping user data safe. It also ensures that the site’s content hasn’t been altered or tampered with, thanks to the encryption provided by the SSL certificate, which stems from the root certificate.

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Types of Root Certificates in SSL

There are two main types of root certificates:

1. Private self-signed certificates issued by a private CA
2. Certificates issued by public certificate authorities

A private self-signed certificate, signed by its issuer, is typically used for internal networks or testing. Because these certificates don’t come from a recognized certificate authority, major browsers won’t trust them by default, so you must manually install them.

On the other hand, public self-signed root certificates are signed by a recognized and trusted certificate authority (CA). Commercial CAs like Sectigo and open-source ones like Let’s Encrypt issue certificates that browsers and operating systems trust by default. These CAs follow an extensive validation process and ensure that only verified entities receive certificates.

The key difference lies in how root stores (the trusted certificate storage in your operating system) recognize them. Private self-signed certificates need extra steps for installation because browsers don’t trust them automatically. In contrast, public CA-issued certificates are already included in most browsers’ root stores.

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How Certificate Authorities Manage Root Certificates

Certificate authorities handle root certificates with high-end precision, as these certificates form the foundation of trust for an entire certificate chain. Here’s how CAs specifically manage root certificates:

1. Issuing Root Certificates: Root certificates are not issued casually. As they sit at the top of the hierarchy, they undergo an extensive vetting process before they are generated. Once a root certificate is created, it becomes the authority that signs other certificates, including intermediate and server certificates.
2. Security and Storage: Root certificates are extremely sensitive and are generally stored offline in Hardware Security Modules. This offline storage isolates them from online threats. These certificates are only brought online when necessary, such as during signing operations, and even then, strict security protocols are followed to minimize risk.
3. Signing: CAs use the root private key to sign other certificates, such as intermediate certificates. This signing process is tightly controlled, with limited access to the root key.
4. Lifecycle Management: Root certificates have long validity periods, often decades, but CAs still actively manage them. They track expiration dates and schedule renewals long in advance to prevent service disruption. CAs also closely monitor any potential vulnerabilities and can revoke a root certificate if it’s compromised, although this is rare due to the high level of security surrounding them.

Revocation: In the unlikely event of a compromise, a CA can revoke a root certificate. However, because revoking a root certificate affects every certificate beneath it, this step is considered a last resort. When a root certificate is revoked, the CA must publish this in a Certificate Revocation List (CRL) or via Online Certificate Status Protocol (OCSP) so systems can stop trusting it immediately.

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Potential Risks and Issues with Root Certificates

Despite the security they provide, root certificates are not immune to risks. A compromised or expired root certificate can cause widespread issues, leading to mistrust and potential breaches in online security.

• Compromised Root Certificates: If a root certificate is compromised, attackers can issue fraudulent certificates that appear valid, tricking users into visiting malicious websites. A notable example occurred in 2011 when the Dutch CA DigiNotar was hacked and issued unauthorized certificates to thousands of users. The CA couldn’t recover from this incident and ceased its existence.
• Expired Root Certificates: When a root certificate reaches the end of its validity period and isn’t renewed, websites that rely on it will show warnings in browsers, causing users to doubt the site’s security. This can lead to a loss of trust and revenue for businesses.
• Certificate Revocation and Path Validation: If a CA revokes a certificate, browsers must be able to quickly check the revocation status to avoid trusting an invalid certificate. Checking a certificate’s validity, called path validation, involves tracing the certificate back to the trusted root and ensuring no issues exist along the way.
• Trust Store Management: Operating systems and browsers maintain a trust store containing a list of trusted root certificates. If a root certificate is removed from the trust store, any certificates issued under it will no longer be recognized as valid. Keeping the trust store updated maintains secure connections.

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Bottom Line

Root certificates, issued by trusted root certification authorities, silently ensure the trust behind every digital certificate we rely on. They secure digital interactions, validate encrypted communications, and provide the integrity of websites and applications.

Root certificates upheld the chain of trust. Without them, our trust in websites, applications, and even email systems would crumble, making online transactions far less secure.

Next time you use your browser, remember that the security behind your connection relies on a CA certificate. Although browsers like Chrome no longer display a padlock icon, the underlying system of trust is still in place, ensuring data and transaction integrity in the background.