What is Private PKI vs. Public PKI? Uses and Key Differences

What is Public CA?

A Public Certificate Authority (Public CA) is a trusted third-party organization that provides digital certificates to verify the identity of entities on the Internet. A digital certificate is also commonly referred to as an SSL/TLS certificate.

Public CAs issue certificates to clients and servers to create secure conversations. Public CAs are trusted organizations, with their certificates trusted by most web browsers, operating systems, and devices.

Public CAs are responsible for authenticating the owner of the certificate, be it a website or server, in addition to ensuring the security and confidentiality of any data shared between the entities.

Also Read: What Is a PKI Certificate? [Detailed Guide]

Public CAs are utilized by the majority of web browsers and operating systems, and therefore all their certificates are trusted out of the box.

In these situations, the Public CA is trusted behind the scenes based on its reputation, compliance to regulations, and the adherence to industry standards, documented by organizations such as the CA/Browser Forum.

The certificates issued by Public CAs are used for more than securing HTTPS connections between client and server. Some typical examples of uses for Public CA-issued certificates include: valid email signatures and authentication, and verifying software applications.

When to Use a Public Certificate Authority?

Public-Facing Websites

Public Certificate Authorities (CAs) are a natural fit for securing any website meant to be consumed by a general, and possibly broad, audience. Even an internal website that has meaningful public-facing features (e.g. eliving.ca) should consider using a Public CA.

Public CA certificates are fantastic for websites that offer e-commerce, banking, financial, and general information. With a Public CA, these kinds of websites will be able to have secure HTTPS connections.

Public CA certificates are recognized by all popular browsers and operating systems and provide encryption for any sensitive information that is exchanged between the user and the website – for example payment method details, or personal information.

Global Recognition

An important takeaway about the use of a Public CA is the level of global recognition. Public CA certificates are trusted directly by all popular browsers, operating systems, or devices, without the need for additional configuration, or manual installation of root certificates.

This level of recognition becomes critical for domains like websites, email servers, and software, where a general level of trust and security is required for a wide variety of users including customers, clients and more external parties that may not have knowledge of or access to your internal services.

SSL/TLS Encryption

Public CAs are often used to secure the transportation of data over the Internet using SSL/TLS encryption.

This provides encryption for sensitive data, such as login names, login passwords, credit card numbers, and other personal data, offered to a website and sent over the Internet from the web server to the user’s web browser or vice versa.

The protocol will protect against any eavesdropping, data tampering, or man-in-the-middle attacks. Therefore, obtaining SSL/TLS encryption is necessary for any service that requires secure communication.

Code Signing

Another use case for a Public CA is code signing. Both developers and software vendors use Public CAs certificates to sign their software to ensure that it hasn’t been altered since its original signature, and it is from a trusted source.

This solves the problem of malware masquerading as legitimate software by assuring that the “code” is real and good, so the user can feel confident downloading and running the software.

Secure Email

Public CAs are also widely used to secure email communications using technologies such as S/MIME (Secure/Multipurpose Internet Mail Extensions).

A Public CA certificate will effectively ensure that none of the content of an email is accessible to unauthorized access by encrypting email messages and applying digital signatures.

Furthermore, this technology supports the verification and identification of the person drafting the email.

Email security is essential for organizations that conduct business involving sensitive communications, ranging from legal documents to contracts and financial discussions.

Global Trust

When an organization needs its certificate to be trusted widely, typically a Public CA offers the best options.

Public certificates come from trusted sources, thus a known Public CA certificate is automatically trusted by devices and browsers, so users are not distracted having to manually install certificates or to configure trust settings.

A publicly trusted certificate supports an organization’s ability to connect and build trust globally, with no distractions creating overhead for manual intervention.

Third-Party Trust

Public certificate authorities (CAs) become particularly necessary in cases when an external party, like customers, partners or suppliers, need to place trust in your communications or services.

For example, if an online retail shop wants customers to trust a secure payment process, then a Public CA certificate is used, and the customers can trust the authenticity and secure communications or services that the shop provides without having to do any manual verification or installation of certificates on their systems.

Simplified Certificate Management

If an organization does not have strong intentions to run a Certificate Authority, then a Public CA can simplify things. Certificates have life cycles that need to be managed such as issuing, renewing, revoking, multiple signing, and including extensive expertise.

Also Read: What is Certificate Lifecycle Management (CLM)?

If an organization uses a public CA, then that expertise and administrative burden are delegated to a trusted third party, leaving the organization with more time for other issues and high-quality security for their communications and data.

What is a Private CA?

A Private Certificate Authority (Private CA) is a trusted internal or organizationally managed entity that issues digital certificates in a limited context or realm. Unlike Public CAs, Private CAs are not trusted or recognized by outsiders or the broader internet community.

Also Read: PKI Certificate Management: Avoid Common Pitfalls & Embrace Best Practices

Private CAs are used for issuing digital certificates in a controlled environment, such as enterprises and internal infrastructures, for secure communications and identity verification processes and other security functions within the organization.

Private CAs operate primarily within an isolated environment, they are primarily reserved for scenarios outside public trust when trusted internal systems or users utilize digital certificates.

Using a Private CA allows an organization greater control over all phases of its certificate management operations, including issuance, renewals, and revocations.

Establishing a company CA will help organizations manage costs, improve security with some level of control over Certificate Authority processes, and meet any needed internal compliance.

Private CAs are usually established by an organization’s IT or security team and are not to be used to establish broad trust for the public.

When to Use a Private Certificate Authority?

Internal Applications and Services

Private Certificate Authorities (CAs) are suitable for securing internal services and applications that are not made broadly available to the Internet or public exposure.

Services such as company intranet websites, internal APIs, internal databases, file servers, and administrative portals are good candidates for private CAs.

Since the resources are only being accessed by employees or systems within the corporate network that you trust, there is no need for worldwide trust.

Utilizing a private CA enables you to manage and issue certificates within your organization. This gives you security and cost control over your non-publicly facing assets.

Device and User Authentication

It is not uncommon for organizations to use private CAs to issue certificates that will authenticate users and devices within the enterprise.

For instance, a private CA could be utilized for issuing a certificate for either VPN authentication (which typically has a strong password and username) or Wi-Fi access authentication, and even login authentication via smart cards or biometric systems.

Private CAs allow only authenticated users or trusted devices to access certain internal resources based on the identity verification methods used by those services.

Securing Internal Communications

When an organization wants to secure machine-to-machine (M2M) communication, even microservices architecture, or data traffic within its internal networks, a private CA can be a cost-effective and flexible solution for these situations.

Private certificates can encrypt internal data traffic and sensitive data, and even authenticate systems communicating across internal infrastructure, without the added cost or complexity that arises when using public CA certificates.

IoT Devices and Embedded Systems

Organizations managing fleets of IoT (Internet of Things) or embedded devices can use a private CA to issue and manage the certificates they need for each device.

This provides certified security for firmware updates, encrypted communication between devices, and certified identity of devices to prevent spoofing or unauthorized access.

Because many IoT devices operate in a closed ecosystem, a private CA can provide organizations the opportunity to customize their security without relying on external trust anchors.

Complete Control Over Certificate Policies

With a private CA, organizations can maintain complete control over their certificate issuance policies, including key length, algorithms, expiration, and revocation.

This is especially useful for organizations that have a unique compliance requirement or must abide by a standard that is different from what a public CA offers.

For a private intermediary CA, organizations can implement their own security policies and evolve their certificate management as risks change.

Cost-Effective for Large-Scale Certificate Issuance

When an organization needs to issue a large number of certificates for something like authentication of employees, servers, or devices, a private CA provides an economical alternative.

Public CA’s charge for every certificate issued, whether the certificate is custom for that employee, server, or device, or whether the organization purchases a wildcard for use.

A private CA allows for unlimited issuance and predictable costs, which scale up for the enterprise environment.

Development and Testing Environments

When developing software, testing, and QA, it is common for models that run in a production-like environment to require SSL/TLS or the use of some authentication mechanisms.

When an organization has a private CA, developers can generate and test secured, encrypted connections and certificate-based authentication, as well as proper integration of PKI without the expense of using public certificates.

Additionally, using a private CA minimizes the chance of accidentally exposing test systems to real-world trust chains.

Meeting Compliance or Regulatory Requirements

In some industries, such as finance, healthcare, and government, tightly controlled usage of cryptographic keys, issuance of certificates, and lifecycle management of certificates is mandated.

A private CA helps organizations to satisfy those compliance or regulatory requirements while providing less monitored usage because it can be visibly powerful and auditable.

It can also be easier to deploy advanced controls such as key escrow, hardware security modules (HSMs), and access logging.

Isolated Environments

In highly controlled environments like defense, critical infrastructure, or classified data centers, systems are isolated from the internet, and a party could not use a public CA because of its lack of connectivity.

A private CA can work solely offline, if required, to securely issue certificates using a PKI system that fully operates in controlled environments that may not use or need external trust chains.

Custom Naming Conventions and Extensions

With a private CA, you can get certificates issued that have custom Subject Alternative Names (SANs), internal domain names (like .local or .corp), and specific extensions relevant to your applications.

Public CAs cannot issue certificates for non-public domain names, so a Private CA is necessary for use cases that require customization.

Difference Between a Public and Private Trust Certificate

Feature	Public Trust Certificate	Private Trust Certificate
Issued By	Trusted Public Certificate Authority (CA)	Internal or Enterprise-controlled CA
Browser/OS Trust	Trusted by all major browsers and operating systems	Not trusted by default; requires manual trust configuration
Use Case	Public-facing websites, e-commerce, external APIs	Internal applications, intranet, VPN, device authentication
Validation Types	DV, OV, EV (Domain, Organization, Extended Validation)	Custom validation based on internal policy
Certificate Cost	Usually paid per certificate or subscription	Cost-effective for bulk issuance, especially in large orgs
Domain Restrictions	Must use publicly registered domain names	Can use internal domains like .local, .corp, etc.
Scalability	Limited scalability due to cost	Highly scalable with no per-certificate cost
Compliance Requirements	Meets global compliance standards (e.g., WebTrust, CA/B)	Meets internal compliance or regulatory requirements
Revocation Mechanism	CRL and OCSP managed by public CA	Custom revocation mechanisms, internal CRL or OCSP
Control Over Policies	Controlled by the issuing CA	Full control over issuance, policies, and lifecycle
Management Tools	Public CA portal or API	On-prem or cloud PKI platforms with internal access
Ideal For	Public websites, customer portals, external communication	Internal services, internal identity and access control

Conclusion

Certera provides both Public CA Certificates and a full Private CA PKI capability to serve all your security and identity needs. With automation, policy controls, and the backing of a team of experts, Certera allows you to deploy digital trust at every layer.

Get started today with Certera and confidently secure your public identity and internal services!