What Is Certificate Authority

Certificate Authorities (CA): The Guardians of Internet Security

Introduction

In today's digital landscape, security is paramount. When you visit a website and see the padlock icon in your browser's address bar, you're witnessing the work of a Certificate Authority (CA). These vital but often overlooked entities form the backbone of internet security and online trust. In this comprehensive guide, we'll explore what CAs are, how they function, who the major players are, and why they're essential for secure online communication.

What is a Certificate Authority?

A Certificate Authority is a trusted third-party organization that issues digital certificates. These certificates serve as digital passports that verify the identity of entities online - primarily websites, but also email addresses, organizations, or individuals.

Digital certificates work on the principles of Public Key Infrastructure (PKI), which uses a pair of keys (public and private) for secure communications:

  • Public key: Available to anyone who wants to send encrypted information
  • Private key: Kept secret by the owner and used to decrypt information

A CA acts as a trusted intermediary that verifies an entity's identity before issuing a certificate binding that entity to a specific public key. This verification process is what creates trust in the global internet ecosystem.

How Certificate Authorities Work

The process of obtaining and using a certificate involves several key steps:

1. Certificate Request Process

When a website owner wants to secure their site with HTTPS, they:

  • Generate a key pair (public and private keys)
  • Create a Certificate Signing Request (CSR) containing their public key and identity information
  • Submit the CSR to a Certificate Authority

2. Identity Verification

The CA then verifies the requester's identity through one of several validation processes:

  • Domain Validation (DV): Verifies only that the applicant controls the domain (typically through email or DNS verification)
  • Organization Validation (OV): Verifies both domain control and limited organization information
  • Extended Validation (EV): The most rigorous process, involving thorough verification of the organization's legal identity

3. Certificate Issuance

After verification, the CA:

  • Creates a digital certificate containing the entity's public key
  • Digitally signs this certificate with the CA's private key
  • Issues the certificate to the requester

4. Certificate Deployment

The website owner installs the certificate on their web server, enabling:

  • Encrypted HTTPS connections
  • Identity verification for visitors

5. Certificate Validation by Browsers

When a user visits the website:

  • The server presents its certificate
  • The browser checks if the certificate was issued by a trusted CA
  • The browser verifies the certificate hasn't expired or been revoked
  • If valid, the browser establishes a secure connection

The Chain of Trust

CAs operate in a hierarchical structure known as the "chain of trust":

Root CA Certificate (built into browsers)
↓
Intermediate CA Certificate(s)
↓
End-Entity (Website) Certificate

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  • Root CAs: The highest level of trust, with self-signed certificates built into browsers and operating systems
  • Intermediate CAs: Issued by root CAs to issue end-entity certificates (this protects the root certificate)
  • End-entity certificates: The certificates issued to websites and services

This hierarchy enhances security by limiting the exposure of root certificates and compartmentalizing risk.

Top Certificate Authorities in the World

The CA market has consolidated significantly over the years. Here are the major players:

1. DigiCert

Market share: ~25%

DigiCert became one of the largest CAs after acquiring Symantec's website security business in 2017. They specialize in high-assurance certificates and serve many Fortune 500 companies.

Key offerings:

  • TLS/SSL certificates (DV, OV, EV)
  • Code signing certificates
  • Document signing certificates
  • IoT device certificates
  • Post-quantum cryptographic solutions

2. Sectigo (formerly Comodo CA)

Market share: ~20%

Sectigo (rebranded from Comodo CA in 2018) is one of the world's largest commercial CAs and has issued millions of certificates.

Key offerings:

  • Complete range of SSL/TLS certificates
  • Email certificates (S/MIME)
  • Code signing certificates
  • Certificate management platform
  • Automated certificate lifecycle management

3. Let's Encrypt

Market share: ~30%

Unlike traditional commercial CAs, Let's Encrypt is a free, automated, and open Certificate Authority created by the Internet Security Research Group (ISRG). Since its launch in 2016, it has revolutionized the certificate landscape.

Key offerings:

  • Free DV certificates
  • Automated issuance and renewal via ACME protocol
  • 90-day certificate validity (encouraging automation)
  • Wildcard certificates

4. GlobalSign

Market share: ~10%

GlobalSign is one of the oldest CAs and a WebTrust-certified certificate authority, focusing on identity and security solutions.

Key offerings:

  • Full range of SSL/TLS certificates
  • Document signing
  • Code signing
  • S/MIME certificates
  • Managed PKI services

5. IdenTrust

Market share: ~5%

IdenTrust is particularly notable as the root CA that cross-signs Let's Encrypt certificates, making them trusted by older devices and browsers.

Key offerings:

  • Legal identity authentication
  • Healthcare identity solutions
  • Financial services identity verification
  • Government authentication

Benefits of Using Certificate Authorities

1. Establishing Trust and Security

The primary benefit of CA-issued certificates is the encryption and security they provide:

  • Data encryption: Prevents eavesdropping and man-in-the-middle attacks
  • Data integrity: Ensures information hasn't been tampered with during transmission
  • Authentication: Verifies the identity of the website or entity

2. Increased User Confidence

When users see the padlock icon in their browser:

  • They know their connection is secure
  • They're more likely to trust the website
  • They're more willing to make purchases or share information

This is particularly crucial for e-commerce sites and financial institutions.

3. SEO Advantages

Google and other search engines give preference to HTTPS websites in their rankings:

  • Better search engine rankings
  • Potential SEO advantage over non-HTTPS competitors
  • Higher click-through rates from search results

4. Protection Against Phishing

Certificates help users verify they're connecting to legitimate websites, not impostor sites designed for phishing attacks.

5. Regulatory Compliance

Many industries have regulations requiring secure connections:

  • PCI DSS for payment processing
  • HIPAA for healthcare information
  • GDPR requirements for data protection
  • Financial industry regulations

6. Universal Browser Compatibility

Certificates from trusted CAs are recognized by all major browsers, preventing users from encountering security warnings.

The Evolution of Certificate Authorities

The CA landscape continues to evolve:

Automation and DevOps Integration

The rise of cloud infrastructure and DevOps practices has driven automation in certificate management:

  • Let's Encrypt pioneered automated certificate issuance with ACME protocol
  • Major CAs now offer APIs and tools for DevOps integration
  • Certificate lifecycle management platforms automate renewals and deployment

Certificate Transparency

Following incidents of mis-issued certificates, Google introduced Certificate Transparency (CT):

  • All certificates must be logged in publicly verifiable logs
  • Improves accountability and enables monitoring
  • Allows domain owners to detect unauthorized certificates

Shorter Certificate Lifetimes

The industry has moved toward shorter certificate validity periods:

  • Maximum validity reduced from 3 years to 398 days (as of September 2020)
  • Encourages automation and more frequent validation
  • Limits the impact of compromised certificates

Post-Quantum Cryptography

With the looming threat of quantum computers:

  • CAs are researching quantum-resistant cryptographic algorithms
  • NIST is standardizing post-quantum cryptography
  • Some CAs already offer hybrid certificates with traditional and quantum-resistant algorithms

Challenges and Controversies

Despite their importance, CAs face several challenges:

Trust Issues

Past incidents have raised questions about CA trustworthiness:

  • DigiNotar bankruptcy after a security breach in 2011
  • Symantec's improper certificate issuance leading to distrust by browsers
  • WoSign and StartCom incidents leading to distrust

Centralization of Trust

The CA model centralizes trust in a relatively small number of entities:

  • Creates potential single points of failure
  • Raises concerns about government influence over CAs
  • Introduces geopolitical considerations in global trust

Alternative Approaches

Several alternative or complementary approaches have emerged:

  • Certificate Transparency: Public logs of all issued certificates
  • DANE (DNS-Based Authentication of Named Entities): Uses DNSSEC to authenticate TLS certificates
  • Certificate Authority Authorization (CAA): DNS records specifying which CAs can issue certificates
  • HTTP Public Key Pinning (HPKP): Though now deprecated, attempted to address CA weaknesses

Conclusion

Certificate Authorities form the foundation of trust on the internet. By verifying identities and enabling encrypted communications, they make secure e-commerce, online banking, and private communications possible.

While the CA ecosystem faces challenges and continues to evolve, its fundamental role remains unchanged: providing the trust infrastructure that enables the secure internet we rely on daily.

For website owners and organizations, understanding CAs helps in making informed decisions about securing online properties. For users, recognizing the role of CAs provides insight into the complex security infrastructure that protects online activities.

As we move forward, the CA industry will continue to adapt to new threats and technologies, maintaining its crucial role in internet security.

This blog post is part of our educational series on web security and PKI infrastructure. Check out our certificate decoder tool to examine SSL/TLS certificates in detail.