What is PKI and How Does it Work?

Public key infrastructure (PKI) is a security framework that uses cryptographic key pairs and digital certificates to authenticate identities, encrypt data, and protect digital communications. It’s the backbone of secure email, online banking, cloud platforms, and nearly every trusted digital interaction.

Today, PKI has evolved beyond foundational infrastructure and is a critical control point for security and compliance. As certificate lifecycles shrink and machine identities rapidly scale, organizations must adjust PKI approaches to prepare for emerging challenges without interrupting operations.

In this guide, we'll explore how PKI creates a secure foundation for digital operations, protecting data, identities, and transactions in a post-quantum future with escalating risks.

• Public key infrastructure is the foundation of digital trust, enabling encryption, authentication, and digital signatures that keep data, devices, and identities secure.
• A PKI system includes certificates, keys, certificate authorities, registration authorities, HSMs, and supporting management software, all of which work together to verify identities and protect sensitive information across systems.
• PKI supports key use cases like SSL/TLS encryption, secure email, document signing, user authentication, IoT security, and machine identity management.
• Benefits of PKI include secure communications, access control, authentication, and code signing to verify software integrity.
• Industries that handle sensitive data like finance, government, and healthcare use PKI systems to comply with strict privacy requirements.
• PKI is now a critical control point for preventing outages, ensuring compliance, and managing the rapid growth of machine identities as certificate lifecycles shrink toward 47 days

Public key infrastructure includes the policies, roles, hardware, software, and procedures required to create, manage, distribute, use, store, and revoke digital certificates. These certificates function like digital passports or driver’s licenses, verifying users, devices, and services before they can connect or share data.

PKI allows users and systems to exchange data securely while confirming the identity of both parties. It protects sensitive activities like online banking, e-commerce, and encrypted email. In today’s IT environments, these systems are essential for cybersecurity and to maintain compliance with data protection laws and regulations. 

For example, when an employee logs on to a company’s internal portal from their home office, PKI encrypts the connection and verifies the server’s identity. It also digitally signs data exchanges to ensure they haven’t been altered in transit. This allows employees and systems to share sensitive information confidently, knowing they’re communicating with legitimate, authorized entities. 

As threats change and quantum computing becomes more real, PKI supports crypto agility. This means organizations can move to stronger encryption standards, including those designed to resist quantum attacks, without disrupting their operations.

PKI is not a single tool, but a system of connected parts. Together, they manage encryption, protect data, and secure communication across users, devices, and services.

The components of public key infrastructure include:

• PKI keys: A key pair used for encryption. This protects data by making it unreadable to anyone except the intended recipient. In cryptography, each public key is paired with a private key. The public key is distributed freely and openly, while the private key is secret to the owner.
• Digital certificates: Electronic credentials that link the certificate holder’s identity to a key pair that can be used to encrypt and sign information.
• Certificate authority (CA): An entity that verifies identities and issues digital certificates.
• Registration authority (RA): Responsible for accepting certificate requests and authenticating the individual or organization behind them.
• Certificate repositories: Secure storage systems that hold digital certificates for lookup and validation.
• Centralized management software: Software that lets organizations manage keys and digital certificates from one place.
• Hardware security module (HSM): Physical devices that perform cryptographic operations and store private keys securely.

PKI works by bringing these components together to enforce trust policies across users, devices, and systems. Through identity verification, encryption, and certificate management, it creates a scalable framework that allows only trusted entities to exchange information.

PKI works through encryption, a subset of cryptography that transforms readable data into an unreadable format with mathematical algorithms.

Encryption algorithms fall into two main categories. Symmetric encryption uses the same key to both encrypt and decrypt data. If that key is compromised, the data is no longer secure.

In contrast, asymmetric encryption uses two linked keys. One is public and shared widely, while the other is private and kept secret. PKI encryption uses this method to encode data, authenticate users, and protect transactions.

The step-by-step process illustrates how PKI works in practice:

1. Each user, device, or system generates a private key (kept secret) and a public key (shared openly).
2. A Certificate Authority (CA) validates the entity’s identity and issues a digital certificate, binding the public key to that identity. Connecting the identity to a key pair supports PKI authentication, which verifies that only trusted users, devices, and systems can access sensitive resources.
3. When sending encrypted data, the sender uses the recipient’s public key. Only the matching private key can decrypt it.
4. The sender may also apply a digital signature using their own private key.
5. The recipient’s system checks the certificate against a CA. It may use a certificate revocation list (CRL) or online status protocol (OCSP) to ensure it hasn’t been revoked, confirming trust in the key. This proves the data’s origin, ensuring integrity and confirming it hasn’t been changed.
6. If a key or certificate is compromised, PKI systems can revoke it, maintaining security across the network.

By verifying identities and securing data, PKI fosters trust among all users. It also prevents man-in-the-middle (MITM) attacks, impersonation, and spoofing. For example, even if an attacker intercepts a message, they cannot decrypt it without the private key.

Organizations can manage PKI without having to invest in significant in-house technological infrastructure or expertise with PKI-as-a-Service (PKIaaS). This cloud-based solution offers scalable certificate management, automated key rotation, and monitoring, helping organizations of all sizes support secure communications and transactions.

Digital Certificates

A digital certificate, sometimes called a “public key certificate,” is an electronic document used to identify the owner of a public key. This allows the recipient to confirm the key came from a legitimate source, mitigating the risk of an MITM attack.

PKI certificates typically include:

• Identifiable information, such as the certificate holder’s name, the certificate’s serial number, and its expiration date
• A copy of the public key, which others can use to encrypt data and verify digital signatures, supporting both confidentiality and authentication
• The digital signature of the issuing CA to confirm authenticity

Proper certificate lifecycle management is critical for maintaining secure data exchange and ensuring that encryption and authentication are functioning correctly. PKI certificates should be tracked and monitored from issuance to expiration, and renewed as needed. Certificate lifecycles will shrink from 398 days to 47 days by March 2029. As 47-day certificates become the new standard, businesses must automate management to ensure certificates are renewed if outdated or revoked if they are compromised.

Certificate Authorities

A certificate authority is a trusted third-party organization that creates and issues digital certificates. They validate identities and help establish trust chains for secure digital communications.

All CAs maintain certificate revocation lists (CRLs), which document certificates revoked before their scheduled expiration date. This helps organizations identify certificates that are no longer valid or secure.

Broadly speaking, there are two types of CAs:

• Root CA: The most trusted entity in a PKI system. Root CAs use self-signed certificates and create the foundation of trust by issuing certificates to subordinate CAs or directly to end users.
• Subordinate CA: These are certified by a Root CA or higher subordinate. These authorities inherit trust and issue certificates to users, devices, or systems. 

Each certificate in the chain is responsible for certifying the authenticity of the next, creating a continuous and reliable trust path from top to bottom. Any compromise among CAs can break this chain, potentially undermining PKI security.

CAs take specific steps to create certificates:

1. Key generation: A user or system creates a public and private key pair.
2. Certificate request: A certificate signing request (CSR) is sent to a CA, including their public key and identity information.
3. Verification: The CA validates the user’s identity, often with the help of an RA. 
4. Certificate issuance: Once verified, the CA issues a digital certificate containing the user’s public key and other identification details. This certificate is also signed by the CA’s private key, creating a digital signature.

Managing these steps at scale requires automation, policy enforcement, and visibility. Certificate services help organizations reduce risk and meet compliance expectations without adding complexity.

Certificate Management Systems

Certificate management systems are software solutions that facilitate all aspects of the certificate lifecycle, from issuance and provisioning to validation, revocation, and renewal. With shrinking certificate lifecycles and higher volumes of machine identities, these tools have become essential to reducing risk, improving visibility, and ensuring that cryptographic assets are managed consistently across environments.

For instance, some solutions keep detailed logs of all related activities, aiding in compliance with regulatory requirements and internal audits. By centralizing management through a single source of truth, organizations can eliminate visibility gaps, reduce the risk of missed expirations, and strengthen control over certificates, keys, and other cryptographic assets.

Automated systems help prevent “certificate sprawl,” where thousands, or even millions, of certificates are deployed across complex, hybrid environments without centralized oversight. As many enterprise PKI environments are fragmented and manually managed, manual processes can’t keep pace. Automation is critical to monitoring certificate expiration dates with shorter lifecycles, handling renewals, and revoking certificates before they introduce risk or cause outages.

Overall, modern certificate management systems serve as a critical control point, helping organizations prevent certificate-related outages, reduce operational risk, and maintain compliance while preparing for future challenges such as post-quantum cryptography.

Hardware Security Modules

HSMs play a pivotal role in PKI’s security architecture. These physical devices protect cryptographic processes by generating, storing, and handling keys in a hardened, tamper-resistant environment.

For example, an HSM can generate a key pair using high-quality random number generators, which are essential to strong encryption. Because the keys never leave the device in plaintext, exposure to threats is minimized.

Another important function is private key storage. Keeping keys within secure hardware protects them from being extracted or compromised by unauthorized entities. This not only protects keys but enables enterprises to enforce stringent security policies at the hardware level. As a result, for enterprises in sectors that require a high assurance of security, such as finance or the government, HSMs are essential in PKI systems to protect data and support trust.

PKI serves as a critical control point for organizations to secure operations as business scales and threats evolve. These are some of the most significant ways organizations leverage PKI to their advantage.

Secure Communication

PKI is a cornerstone for protecting various forms of digital communication, including email, messaging services, APIs, and cloud-based workloads. Not only does it safeguard these channels, but it also ensures trusted interactions between consumers, partners, employees, and systems.

As organizations scale digital services and adopt shorter-lived certificates, maintaining secure, uninterrupted communication is dependent on effective certificate lifecycle management to prevent outages and vulnerabilities.

Authentication and Access Control

PKI provides strong authentication mechanisms for users, devices, and a growing number of machine identities accessing systems, networks, and online services. Certificates serve as secure digital identities, ensuring access is granted only to verified entities, both human and machine.

These capabilities make PKI a key part of a Zero Trust security model. By integrating PKI into a Zero Trust strategy, organizations can continuously verify identities, strengthen compliance, and reduce the risk of cyber threats, all while maintaining control as complexity increases, and number of identities grows.

Document Signing and Timestamping

Digital signatures powered by PKI verify the authenticity and integrity of electronic documents, supporting secure and compliant digital transactions. This is essential for legal paperwork, contracts, and other records where proof of originality, confidentiality, and consent is required.

Document signing certificates serve three key purposes:

• Authenticity: The certificate confirms the document has been signed by the individual or entity that holds the corresponding private key to the public key in the certificate.
• Integrity: Any alteration to the document after it has been signed invalidates the digital signature. This ensures the document received is exactly what the signer had intended to send, without any modifications.
• Non-repudiation: The signer cannot deny the authenticity of their signature on a document, as the digital signature and the associated certificate provide strong evidence of the signer’s identity and their agreement with the document contents at the time of signing.

In addition to strengthening trust, digital signatures improve operational efficiency. Up to 80% of agreements with digital signatures are completed in less than a day, and 44% in less than 15 minutes. This enables organizations to complete agreements faster while maintaining security and compliance.

Code Signing

Software developers use code signing certificates to authenticate their scripts and applications. This allows users to verify that software has not been altered. As software delivery pipelines accelerate, PKI helps maintain trust across enterprise environments.

Software Integrity

PKI is used to verify the origin and integrity of software, ensuring that applications, drivers, and updates haven’t been compromised during distribution. This becomes especially critical as release cycles shorten and environments grow. Even a single compromised or expired certificate can introduce significant security risk.

Internet of Things (IoT) and Machine Identities

“Smart” devices and connected workloads are now central to modern infrastructure but also introduce additional security challenges and risks. By providing each device, workload, or system with a unique digital certificate, PKI establishes trusted identities at scale. This prevents unauthorized access, spoofing, and data manipulation across distributed environments.

As machine identities, including APIs, services, and AI-driven agents, continue to grow rapidly, PKI supports secure authentication and communication across complex, fragmented ecosystems. However, this also increases the need for centralized visibility, automation, and governance to effectively manage certificate lifecycles.

Beyond authentication, PKI enables end-to-end encryption for data in transit, ensuring that communications between devices, applications, and cloud workloads remain secure, trusted, and resilient.

PKI is essential in sectors that face unique threats and where data breaches carry severe legal, financial, and regulatory consequences.

• Finance relies on PKI for secure online banking, transaction authentication, and compliance with strict KYC (Know Your Customer) and AML (Anti-Money Laundering) requirements. Strong digital certificate security protects customer data during transfers, verifies identities in high-value transactions, and helps prevent fraud and unauthorized access. Centralized visibility and automated lifecycle management are becoming essential to ensure compliance, reduce operational risk, and keep pace with growing machine identities across banking ecosystem.
• Government agencies rely on PKI for secure communications, digital signatures on official documents, and verifying citizen identities. It also supports secure online services such as tax filing, licensing, and access to public benefits. As digital government services expand and certificate volumes grow, PKI becomes critical for maintaining trust, ensuring data integrity, and meeting regulatory requirements across departments and systems.
• Healthcare organizations use PKI to secure electronic health records (EHR), comply with HIPAA regulations, and authenticate medical devices across networks. It also ensures confidentiality during telemedicine appointments and within patient portals. PKI helps maintain data integrity and availability across a growing number of medical devices and digital health services. This makes modernization efforts like automation and centralized management necessary to support compliance in highly regulated environments.
• Large enterprises with distributed workforces use PKI for email encryption, VPN access, application security, and device authentication. It ensures that only verified users, devices, and systems can access critical resources. As enterprises scale across cloud and environments, the number of certificates and machine identities continues to grow rapidly. PKI helps reduce reliance on manual processes, prevent certificate-related outages, and maintain visibility and control across enterprises.

These best practices help strengthen your PKI implementation and support secure certificate management.

• Keep policies and procedures updated: Certificate policies (CP) and certification practice statements (CPS) are essential to PKI. The CP is a comprehensive document that outlines the different classes of certificates issued by a Certificate Authority and their applicable policies. The CPS details how the CA implements these policies in a technical capacity. Keeping these documents up to date is fundamental to maintaining security, trust, and legal compliance. They should be regularly reviewed and revised to align with the dynamic landscape of cybersecurity, technology, and regulatory changes.
• Protect private keys: Strong mechanisms like HSMs provide physical and logical protection against tampering and unauthorized access.
• Practice regular key rotation and renewal: Keys and certificates should not be used indefinitely. Establish a routine for regular key and certificate rotation to mitigate the risks associated with key exposure and avoid unexpected expirations. This type of crypto agility is increasingly essential to prepare for post-quantum threats, as bad actors seek to harvest data now and decrypt it when quantum computers with the capability to crack current algorithms are available.
• Implement strong authentication schemes: Require multi-factor authentication (MFA) to enhance security to access PKI systems and perform sensitive operations such as certificate issuance or revocation.
• Centralize certificate and key management: Implement tools and processes that provide greater visibility and control for managing the entire lifecycle of certificates, from issuance to revocation. This also supports audits and compliance by enabling transparency and traceability.
• Set key backup and recovery policies: Establish and regularly test backup and recovery procedures to confirm that critical PKI components can be restored quickly and securely after a disruption or disaster.

Managed PKI services are useful for organizations that need PKI but don’t have the expertise on hand. In these situations, a managed PKI vendor helps manage the policies, hardware, and software to ensure the PKI is being operated in a way keeping with best practices.

Cloud PKI is a service-based deployment model where the Certificate Authority (CA), key management, and lifecycle tools are hosted by a provider. Organizations can deploy and manage digital certificates without the need to invest in or maintain their own physical infrastructure. Compared to on-premises PKI, which offers full control but requires significant cost and IT resources, cloud PKI provides faster deployment, easier scaling, and simplified management.

Cloud PKI is a strong fit for enterprises with large or distributed IT environments. It enables faster certificate issuance, supports automated lifecycle management, and improves visibility for compliance.

There are also hybrid deployment models. Hybrid PKI deployments combine cloud-based services with on-premises infrastructure. This model gives organizations greater flexibility, allowing them to maintain control over sensitive components while benefiting from the scalability of the cloud.

Organizations should choose the model that aligns with their resources, priorities and goals; helps them keep up with regulatory requirements and can adjust to shifting workloads.

Public key infrastructure will remain the foundation of digital trust as cryptographic methods evolve. However, as technology and business demands accelerate, PKI must also evolve.

With the rapid approach of quantum computing, today’s public key algorithms will no longer be secure, threatening the confidentiality and integrity of digital communications. At the same time, organizations are managing significantly more certificates with shorter lifecycles. This places additional pressure on PKI operations, especially those with manual processes.

NIST released the first post-quantum encryption standards in 2024 to help standardize algorithms designed to resist quantum attacks. These new standards will reshape how organizations protect identities, data, and transactions. Transitioning to post-quantum cryptography requires careful planning, centralized control, and scalable lifecycle management.

To stay ahead, organizations need PKI systems that provide greater visibility, support automation, and allow new algorithms to be integrated without disruption. As lifecycles move toward 47 days, PKI becomes a critical control point for maintaining security, uptime, and compliance in the face of evolving threats.

Entrust offers a variety of PKI software solutions, including cloud-native PKI as a Service (PKIaaS), managed PKI services options, and our on-prem PKI solution, Entrust Certificate Authority. These enable your organization to balance enablement and security based on your unique needs and digital ecosystem.

For organizations seeking a comprehensive solution for all of your cryptographic security management needs, Entrust’s Cryptographic Security Platform provides all the critical components of public key infrastructure, combined with certificate lifecycle management, key and secrets management, and HSMs into one powerful, centralized management interface.

Experience the platform for yourself by checking out our interactive demo today.