What is PKI Authentication? How PKI Authentication Works

It seems counterintuitive that a cybersecurity framework developed in the 1970s is arguably more needed now than ever before to secure modern enterprises. But that’s exactly the case with public key infrastructure (PKI).

In this guide to public key infrastructure authentication, we’ll dive into what PKI authentication is, how PKI authentication works, and the benefits of using PKI authentication.

What Is PKI?

Before diving into PKI authentication, it’s important to first understand public key infrastructure (PKI).

Put simply, PKI is a framework of certificate authorities (CAs), registration authorities (RAs), key management systems, policies, and validation mechanisms that issue, validate, and revoke digital certificates.

Perhaps without even realizing it, you likely interact with PKI daily, such as when connecting to a website, where your browser leverages PKI to verify that a website can be trusted before engaging in encrypted communication.

What Is PKI Authentication?

PKI authentication is the process of verifying users, devices, or systems by leveraging public key infrastructure. PKI authentication uses digital certificates and asymmetric cryptography to confirm the identity of a user or device before granting access to a network or resource. 

PKI uses asymmetric cryptography, which functions through pairs of public and private keys. A certificate binds a public key to an identity and is digitally signed by a trusted CA. Authentication occurs when the certificate chain and proof-of-private-key possession are validated.

For enterprises, PKI authentication is important today for securing Wi-Fi or other network access using 802.1X authentication, rather than just relying on usernames and passwords.

In particular, as the number of devices grows, such as in BYOD environments and with the proliferation of Internet of Things (IoT) devices, it’s important to have a framework that helps ensure the right users and devices are connecting to your network.

How PKI Authentication Works

PKI authentication relies on certificates to prove identity, such as that of a user, device, or website. In that sense, a certificate is like a driver’s license used as ID. But just as there are parties and processes behind issuing driver’s licenses and authenticating them, the same goes for digital certificates.

So, with PKI authentication, the main steps and parties involved include the following:

1. Certificate issuance: First, you need a trusted party to issue certificates. This could be a third-party known as a certificate authority (CA), which is often used in the context of website certificates. But within a corporate network, you might have an internal CA that issues certificates to each device you want to grant access to.
2. Public and private key generation: Generally, to get a certificate issued, a public and private key are first generated by the relevant device/software/site/etc. that will need to prove its identity. That party then sends the public key to the CA while hanging onto the private key in a secure storage location, such as a TPM (Trusted Platform Module) on a computer. (So, steps 1 and 2 are somewhat out of order here, but they’re intertwined).
3. Authentication request: This is the meat of the PKI authentication process. When trying to access a protected resource — like a laptop connecting to a corporate Wi-Fi network that relies on 802.1X certificate-based authentication instead of just a password — the laptop needs to prove its identity. In this case, a RADIUS server generally requests the certificate from the laptop and checks the certificate against its trusted CA.The certificate also contains the public key. As part of the authentication process, the server also issues a cryptographic challenge that the laptop signs using its private key. The server then verifies this cryptographic math by using the public key to verify that the challenge was signed by the owner of the aligned private key.

If the authentication request goes through successfully, then the device can connect to the network/website/etc., often via TLS (Transport Layer Security). PKI authentication in EAP-TLS occurs within the TLS handshake itself. TLS is an encryption protocol, such as for moving data between a VPN and corporate network.

PKI authentication is the process of verifying identity; encryption (TLS) is a subsequent protocol that uses those verified keys. But PKI authentication gives the green light to start an encrypted connection, with the public and private key used to exchange a session key. As such, PKI is considered essential for modern encryption.

Common Use Cases for PKI Authentication

PKI authentication supports a wide range of security applications across modern IT environments. Its strong identity verification and encryption capabilities make it a common framework for securing communications, systems, and digital assets for enterprises.

Secure Email Communication

PKI enables encrypted and digitally signed email communications. Technologies like S/MIME rely on PKI to implement certificates to ensure that only verified users can send emails and that the emails can’t be altered during transmission.

VPN Access

Many organizations use PKI authentication to secure VPN access. Instead of relying on passwords alone, VPN clients can authenticate using device or user certificates, ensuring only trusted devices and users can establish secure connections to corporate networks. 

Digital Signatures

PKI is widely used to create digital signatures for documents, transactions, and software releases. These signatures verify the identity of the signer and confirm that the content has not been altered.

IoT Device Security

The number of connected devices on modern networks is only increasing, meaning PKI authentication is even more important for securing IoT environments. Each device can be issued its own certificate, allowing networks to verify that only authorized devices are allowed to communicate. This practice helps prevent rogue devices from joining the network and reduces the risk of large-scale IoT security breaches.

Securing Websites

One of the most familiar uses of PKI is securing websites through HTTPS. Together with PKI, SSL/TLS certificates enable browsers to verify a website’s identity and establish encrypted connections with servers, protecting sensitive data like login credentials, payment information, and personal data from interception.

Software and Code Authenticity

Software developers often use PKI-based code signing to verify that applications and updates come from trusted sources. When the software is signed with a certificate, operating systems and users can verify the publisher’s identity and confirm the code has not been modified since its release.

PKI Authentication Benefits

Because PKI validation is based on cryptography, it’s inherently more secure than password-based authentication, which can easily be intercepted or cracked.

As a result, PKI authentication improves both security and scalability for enterprise networks, making it safer and more practical for organizations to manage device access, protect data, and enforce strong identity verification across systems. 

These are some of the most common ways organizations benefit from PKI authentication. 

Manage BYOD Environments

Many companies allow employees to use their personal devices for work, especially smartphones that might supplement a work-issued computer. While that can add convenience, it can also introduce new security risks, as you don’t want any random device to be able to connect to your network.

So, to let BYOD devices connect securely, companies can use PKI authentication, where enrolled devices get issued device-specific certificates. When those devices try to connect to the corporate network, PKI authentication means they cryptographically prove they’re in possession of the private key that verifies the certificate’s legitimacy.

And if the device gets stolen or other security issues pop up, enterprises can use software like SecureW2 that makes it easy to dynamically revoke certificates.

Implement 802.1X Network Access

Under 802.1X, the supplicant authenticates through an authenticator (switch/AP), which forwards EAP messages to a RADIUS authentication server. And the gold standard for 802.1X authentication uses EAP-TLS, which relies on PKI authentication.

With EAP-TLS, the device proves its identity via a certificate and a mutual TLS handshake, which, as mentioned, is initiated via the cryptographic proof stemming from PKI.

Support Interoperability and Scalability

PKI is built on widely adopted cryptographic standards, allowing certificates to be recognized across different systems, platforms, and vendors. This interoperability makes it easier for organizations to deploy PKI authentication consistently across large enterprises and complex device environments, helping to maintain strong security controls as their networks grow. 

Reap Additional Security Advantages

Beyond enabling secure network access, PKI authentication also provides several broader security benefits to help enterprises protect sensitive systems and data. 

• Authenticate data sources: Systems can verify that data or communications come from a trusted source. Certificates bind cryptographic keys to identities to prove that users, devices, or services interacting with a network are legitimate. 

• Maintain data privacy: Through encryption protocols like TLS, PKI authentication protects sensitive information while it’s in transit, ensuring communications remain confidential. 

• Resist phishing and credential-based attacks: Because PKI authentication requires possession of a private key, rather than a password, it is far more resistant to phishing, credential theft (brute force attacks), and man-in-the-middle attacks. 

• Strengthen overall enterprise security: Replacing password-based authentication with certificate-based identity verification helps organizations implement stronger security models like zero-trust architectures. 
• Enable non-repudiation: PKI validation can support digital signatures that prove a specific user or device performed a particular action. Because only the certificate holder possesses the private key used to sign, they can’t deny that the action happened. 

Limitations of PKI Authentication

While PKI authentication provides strong security benefits, it has its own set of challenges, particularly around managing and maintaining the system.

Infrastructure Complexity

One of the largest limitations of PKI is the complexity of managing the infrastructure internally. Organizations must establish certificate authorities, define policies, manage certificate lifecycles, and maintain trust chains. 

Without the right tools or expertise, managing these components can become difficult quickly. Managed PKI services can help reduce this complexity by automating many of these processes and leveraging the expertise of the third-party provider.

Risk of Key Loss

PKI security relies on private cryptographic keys. If these keys are lost or corrupted, organizations may lose access to the data associated with them. As a result, PKI system managers must implement proper key backup and recovery procedures to prevent potential data loss.

Performance Considerations

PKI encryption and authentication processes require computational resources. As systems scale to support larger numbers of devices and authentication requests, this additional processing can create performance overhead. While modern hardware and optimized implementations mitigate many of these concerns, organizations — particularly if managing PKI internally — should plan for the resource demands of large-scale PKI deployments.

Simplify PKI Authentication with SecureW2

PKI authentication helps improve security, but it can be challenging to manage certificates, especially if you’re trying to scale device connections and adapt to security threats.

SecureW2 simplifies this through an integrated platform that includes aspects such as a cloud RADIUS server and dynamic PKI management system. The cloud RADIUS server validates certificates against the trusted CA and revocation sources in real-time rather than relying on whenever the server was last manually updated.

Ultimately, SecureW2 enables you to move to a continuous trust architecture based on PKI authentication, without the operational complexity that can otherwise be associated with this framework.

Schedule a demo of SecureW2’s passwordless platform today to see how it can save you time while strengthening security.