What is PKI Authentication? How PKI Authentication Works

Organizations use PKI-based authentication to secure networks and asset access, reducing risks like phishing and credential theft. While PKI authentication is highly secure and scalable, successful implementation requires careful certificate management, key protection, and infrastructure planning. For modern enterprises, a cybersecurity framework from the 1970s is more relevant now than ever before. Does that seem counterintuitive? Yes — but it’s exactly the case with public key infrastructure (PKI).

In this guide, we’ll dive into what PKI and PKI authentication are, how PKI authentication works, common use cases, and its benefits and limitations. By the end, you’ll know exactly why this vintage security process is still so relevant today.

What Is Public Key Infrastructure (PKI)?

Public Key Infrastructure (PKI) is a framework for the issuance, validation, and revocation of digital certificates, regulating secure access to resources and networks. 

It relies on many components and systems, including certificate authorities (CAs), registration authorities (RAs), asymmetric cryptography, key management systems, policies, and validation mechanisms, to securely authenticate and authorize users.

You probably interact with PKI daily. For example, when you connect to a site’s web server, your browser uses a specific type of PKI certificate, known as a Secure Sockets Layer (SSL) certificate or Secure Sockets Layer/Transport Layer Security (SSL-TLS) certificate, to verify the website’s validity and trustworthiness before engaging in encrypted communication.

What Is PKI Authentication?

Public key infrastructure authentication (PKI authentication) is the process of verifying the identity of users, devices, or systems using digital certificates issued within public key infrastructure. It protects networks and resources from unauthorized access. 

PKI uses asymmetric cryptography, where a public key encrypts the data and a matching private key decrypts it.(In symmetric encryption, you use the same key to both encrypt and decrypt.) 

A trusted CA digitally signs each certificate, binding a public key to an identity. When the server validates the certificate chain and proof of private key possession, it authenticates users or devices, granting appropriate access.

One example of PKI authentication is 802.1X authentication, which uses certificates for port-based access control. Modern enterprises prefer 802.1x over traditional credentials (usernames and passwords) for more network access, including Wi-Fi.

As organizations expand access for Bring Your Own Device (BYOD) policies and Internet of Things (IoT) devices, they need PKI authentication to ensure only authorized users and devices can access their networks and resources.

How PKI Authentication Works

Using PKI certificates, organizations can prove the identity of users, devices, or websites. Each digital certificate is like a driver’s license: it’s a verifiable form of ID that only regulated parties and processes can issue and authenticate.

Here are the necessary steps that make PKI-based authentication work:

Phase 1: Select Certificate Authorities

First, you need a trusted party to issue certificates. This is typically a Certificate Authority (CA), a third-party entity that governs and issues certificates. Alternatively, many organizations use an internal CA to manage and issue certificates specifically for their own approved users and devices.

Phase 2: Generate Public and Private Keys

The next step is generating public and private keys for asymmetric encryption. Typically, the device, software, or website needing to prove its identity generates these keys, sending the public key to the CA while storing the private key in a secure location, such as a computer’s TPM (Trusted Platform Module).

Phase 3: Client Authentication Request and Authorization

When a device or service wants access, it attempts to prove its identity to the authenticating server (often a RADIUS server). 

For example, let’s say a laptop wants to connect to a corporate Wi-Fi network using 802.1X certificate-based authentication. 

1. The laptop sends a network access request
2. The RADIUS server requests the laptop’s client certificate 
3. The laptop sends the certificate, containing its public key
4. The RADIUS checks the certificate against its trusted CA’s certificate database and user directory, then issues a cryptographic challenge to the laptop
5. The laptop responds to the cryptographic challenge, deciphering it with its private key
6. The RADIUS server uses the public key to verify that the challenge was successfully decrypted and signed by the owner of the matching private key — if aligned, the server grants conditional access based on live access policies
7. The laptop connects to the network with authorized permissions

This example is based on a common, highly secure authentication method known as Transport Layer Security (TLS) — more specifically, Extensible Authentication Protocol-Transport Layer Security (EAP-TLS). 

Public key infrastructure authentication is the process of verifying digital identities, giving the green light to start an encrypted connection by exchanging the public and private key to obtain a session key. The TLS encryption protocol then uses those verified keys to govern access.

PKI authentication, encryption, and authorization work hand in hand to securely verify identities and control access to resources and networks.

Common Use Cases for PKI Authentication

Modern IT environments rely on PKI authentication to verify identities and encrypt sensitive data, ensuring that all digital assets and communications remain secure. Here are some common use cases:

• Secure email encryption: Technologies like Secure/Multipurpose Internet Mail Extensions (S/MIME) rely on digitally signed PKI certificates to ensure only verified users can send emails and sent emails can’t be altered. 
• VPN access: VPN clients can authenticate using device or user certificates instead of credentials, ensuring only trusted devices and users establish secure connections to corporate networks. 
• Digital signatures: Used for documents, transactions, software releases, and more, authenticated electronic signatures verify the signer’s identity and confirm the content hasn’t been altered.
• IoT device security: Each connected device receives its own certificate, preventing rogue device connections that may lead to large-scale IoT security breaches.
• Secure website access: SSL/TLS certificates establish HTTPS connections, allowing web browsers to verify a website’s identity and encrypt sensitive data like personal information, login credentials, or payment details.
• Software and code authenticity: Using certificates to code-sign software allows operating systems and users to verify the publisher’s identity and confirm the code hasn’t been modified since its release.

Benefits of Public Key Infrastructure Authentication

PKI identity verification is a safer, more practical alternative to password-based authentication. For enterprises managing an increasing number of devices, users, and types of sensitive data, PKI authentication is easier to scale, too.

Organizational benefits of PKI authentication include: 

Data Privacy Through Encryption

Encryption protocols like EAP-TLS protect sensitive information in transit, ensuring digital communications and data remain confidential.

Reliable Data Source Authentication

Digital certificates bind cryptographic keys to identities, proving that users, devices, or services interacting with a network are trusted sources.

Improved BYOD Management

PKI validation lets organizations issue device-specific certificates for enrolled BYOD devices, such as personal smartphones or laptops. With the correct certificate and corresponding private key, each device cryptographically proves its identity.

If devices are lost, stolen, or compromised, advanced tools like JoinNow Dynamic PKI make it easy to dynamically revoke certificates.

Secure 802.1X Network Access

While it supports many authentication protocols, the gold standard for 802.1X authentication is EAP-TLS, which leverages digital certificates and mutual TLS handshakes to prove device identity. 

Pairing 802.1X with EAP-TLS provides reliable identity verification and secure communications.

Resistance to Phishing and Credential-Based Attacks

Because PKI authentication requires possession of a private key, it’s far more resistant to phishing, credential theft (brute force attacks), and man-in-the-middle attacks when compared to password-based authentication methods.

Widespread Enterprise Security

By replacing passwords with certificate-based identity verification, organizations can build a Zero Trust Network Architecture (ZTNA). This continuous trust model offers far stronger security than traditional, one-time authentication systems

Genuine Non-Repudiation

PKI validation supports digital signatures that prove a specific user or device performed a particular action. Since only the certificate holder possesses the private key used to sign, they can’t deny the action occurred.

Interoperability and Scalability

Public key infrastructure is built on cryptographic standards that allow diverse systems, platforms, and vendors to recognize and verify each certificate. 

For enterprises, this interoperability makes PKI authentication deployment easier because it works consistently across all systems, including complex device environments and rapidly growing networks.

Limitations of PKI Authentication

While PKI authentication provides strong security benefits, it has challenges, too, particularly with system management and maintenance.

Infrastructure Complexity

Internal infrastructure management is one of PKI’s biggest limitations. From upfront work establishing certificate authorities and installing hardware to ongoing certificate policy definition, trust chain maintenance, and lifecycle management, it’s a lot to handle, especially without the right tools or expertise.

Managed PKI services remove complexity through CA management and process automation, reducing manual work for your organization.

Risk of Key Loss

PKI security relies on private cryptographic keys that you must never share. If these keys are lost or corrupted, you may lose access to associate data.
That’s why PKI system managers must design, implement, and maintain proper key backup and recovery procedures.

Performance Considerations

Public key encryption and authentication requires computational resources. As systems scale to support more devices and access requests, performance overhead increases.

If managing PKI internally, organizations must plan for the increasing demands of large-scale PKI deployments by implementing process and hardware improvements.

Simplify PKI-Based Authentication with SecureW2

Certificate management system upkeep is challenging, especially while scaling and adapting to modern security threats.

SecureW2 simplifies PKI with an integrated platform combining the scalability of our Cloud RADIUS servers with the reliable security of our Dynamic PKI management system. Instead of relying on data from your server’s last manual update, our system validates certificates against the trusted CA and revocation sources in real time. 

With SecureW2, you get enterprise-grade continuous trust architecture without the operational complexity of internal on-prem PKI.

Schedule a demo to see how our passwordless platform can strengthen security, reduce costs, and save you valuable time.