What is PKI and why is it important?

The number of connected IoT devices in corporate networks is growing fast. That growth brings plenty of benefits — better efficiency, smarter decision-making, and improved customer service — but also major security challenges. Connecting thousands of IoT devices safely and managing access across different network segments isn’t simple.

This is where Public Key Infrastructure (PKI) plays an important role. PKI helps organisations build a trusted and secure digital environment by verifying identities and encrypting communication between systems, users, and devices.

What is PKI?

PKI, or Public Key Infrastructure, is a system of policies, procedures, and technologies that use digital certificates and encryption to secure digital communication. It ensures that data exchanged between users, devices, and applications is confidential, tamper-proof, and verified.

At its core, PKI enables organisations to:

• Authenticate identities of users, devices, and services
• Encrypt data in transit to prevent eavesdropping
• Guarantee data integrity so it cannot be altered undetected
• Provide non-repudiation, ensuring that digital transactions cannot later be denied

PKI is fundamental for building trusted networks, particularly when scaling IoT, OT, or enterprise applications.

Core components of PKI

PKI consists of several interdependent elements that work together to establish trust:

• Digital certificates act like electronic ID cards, proving the identity of users, servers, or devices. They are based on cryptographic keys that allow secure communication.
• Certificate authorities (CA) are trusted entities responsible for issuing and signing certificates. Many organisations use a root CA as the ultimate trust anchor, which may remain offline for security, supported by intermediate CAs that handle day-to-day issuance.
• Registration authorities (RA) assist CAs by validating identity requests before certificates are issued.
• Verification authorities (VA) check certificates in real time, including revocation status via CRL (Certificate Revocation List) or OCSP (Online Certificate Status Protocol).
• Finally, all certificates and their statuses are stored in a certificate database, ensuring traceability, management, and validation.

Together, these components form a trust chain, linking each certificate back to a trusted root CA.

How Public Key Infrastructure works

When a user or device requests a certificate, the RA first verifies their identity. Once approved, the CA issues and digitally signs the certificate, which is stored in the certificate database.

When communication occurs, the VA validates the certificate, confirming it is still valid and hasn’t been revoked. Encrypted communication can then proceed using public and private keys, ensuring that only authorised parties can read or modify the transmitted information.

This workflow protects both the integrity and confidentiality of data while allowing systems to trust one another.

Encryption in PKI

PKI uses a combination of symmetric and asymmetric encryption.

Symmetric encryption

Symmetric encryption uses a single shared key to encrypt and decrypt data, providing fast and efficient protection for large amounts of information. In PKI, this key is typically exchanged securely using asymmetric encryption.

Asymmetric encryption

Asymmetric encryption, or public key cryptography, uses a pair of keys: a public key for encryption and a private key for decryption. This allows secure communication without sharing secret keys directly and is commonly used to establish trust and protect the symmetric session key.

By combining both methods, PKI delivers scalable security suitable for large networks and complex digital ecosystems.

Certificate lifecycle

Managing certificates throughout their lifecycle is critical to maintaining trust:

• Issuance: Certificates are created and signed by the CA after verification.
• Renewal: Certificates must be refreshed before expiration to maintain secure operations.
• Revocation: Compromised or no-longer-needed certificates are revoked to prevent misuse.
• Automation:Managed PKI solutions automate these processes, reducing human error and operational burden.

Effective lifecycle management ensures that certificates remain trustworthy and networks stay secure.

Key storage and protection

Private keys underpin the security of PKI. Organisations use Hardware Security Modules (HSMs) to protect these keys from compromise. HSMs provide secure storage, backups, and controlled access, ensuring that even if systems are breached, private keys remain safe.

Strengthening your security with PKI

PKI provides a solid foundation for protecting data, authenticating devices, and maintaining trust across your digital environment. It’s a key building block of modern network and IoT security. For practical examples, real-world applications, and advice on PKI implementation, see our blog: PKI in practice.

If you’d like to learn more about how PKI can support your organisation, get in touch with our team or explore our PKI technology partners.