---
title: Public Key Infrastructure (PKI) explained simply
description: Public Key Infrastructure (PKI) secures digital communication with certificates - basics, advantages and possible applications explained in compact form.
image: https://rheintec.io/hubfs/public-key-infrastructure-digital-security-network-lock.jpg
---

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# Public Key Infrastructure (PKI): Security Through Digital Trust Anchors

[ Alexander Thies ](https://rheintec.io/en/it-security-blog/author/alexander-thies)  - Mar 27, 2026 10:46:57 AM

In today's digital world, it is essential not only to store and transfer data, but also to protect it reliably. The so-called **Public Key Infrastructure** - **PKI** for short - plays a central role in this. But what is a PKI, how does it work and what advantages does it offer companies and organizations?

## What is a PKI?

Public Key Infrastructure is a system for the secure management of digital keys and certificates. The aim is to secure digital communication through encryption, authentication and integrity. This is done using so-called public key procedures, in which a key pair - consisting of a public and a private key - is used.

A user can create a private key and a certificate signing request (CSR). The Certificate Authorities (CAs) check this request and then issue the requested certificate, thus ensuring trust in digital identities. The PKI is therefore a kind of digital trust network.

![Digitales Zertifikat auf Monitor in moderner IT-Umgebung zur Darstellung von PKI](https://rheintec.io/hs-fs/hubfs/digitales-zertifikat-auf-bildschirm-it-sicherheit-pki.jpg?width=1456&height=816&name=digitales-zertifikat-auf-bildschirm-it-sicherheit-pki.jpg)

## The basics of the Public Key Infrastructure

The central **Public Key Infrastructure basics** include the following components:

- **Certification authority (CA)**: Issues and signs digital certificates.
- **Registration authority (RA)**: It verifies the identity of the applicant.
- **Certificate database**: Stores issued, revoked and expired certificates.
- **Directory service**: Enables access to public keys and revocation lists.
- **PKI client software**: Utilizes the infrastructure on the user side.

A well-structured **PKI environment** is based on clearly defined roles and processes. In companies in particular, a **PKI admin** is often responsible for the operation, maintenance and security of this infrastructure.

## Why a two-tier PKI?

Many organizations rely on a **two-tier PKI**, consisting of a Root CA and one or more Intermediate CAs. The root CA is offline and rarely active. It only signs the intermediate CAs, which in turn are responsible for issuing operational certificates.

This separation increases security: if an intermediate CA is compromised, it can be withdrawn without jeopardizing the root CA. A two-tier structure makes the **PKI security** more robust against attacks.

![Skizzierte PKI-Struktur mit Root-CA und Zertifikathierarchie auf Whiteboard erklärt](https://rheintec.io/hs-fs/hubfs/pki-struktur-root-ca-whiteboard-schema.jpg?width=1456&height=816&name=pki-struktur-root-ca-whiteboard-schema.jpg)

## What is Managed PKI?

**Managed PKI** is the outsourcing of the entire public key infrastructure to a specialized service provider. This service provider takes over administration, maintenance, scaling and security measures. For many organizations that do not have their own PKI expertise, this is an attractive alternative to in-house operation.

Managed solutions offer advantages in terms of scalability and compliance, for example in regulated industries such as healthcare or finance. However, trust in the provider must also be guaranteed here.

![IT-Experte verwaltet Managed PKI über Konsole im sicheren Cloud-Rechenzentrum](https://rheintec.io/hs-fs/hubfs/managed-pki-cloud-rechenzentrum-admin-konsole.jpg?width=1456&height=816&name=managed-pki-cloud-rechenzentrum-admin-konsole.jpg)

## Security of PKI systems

The question often arises: **How secure is PKI?** The answer is: very secure - provided it is implemented and maintained correctly. The strength of the public key infrastructure lies in the mathematical process of asymmetric cryptography. However, human error, outdated certificates or inadequate key management can jeopardize security.

Regular audits, training and a solid policy basis are therefore required to operate **public key infrastructures** securely in the long term.

## PKI application scenarios

PKI is no longer just an issue for large companies. SMEs are also increasingly relying on certificate-based security, e.g. for

- Secure e-mail communication via S/MIME
- VPN authentication
- Digital signatures
- Device identification in the IoT environment
- Web server certificates (HTTPS)

PKI is becoming increasingly important, especially in the Internet of Things: authentication and encryption between machines and devices (M2M communication) can be reliably implemented with certificates.

![Vernetzte IoT-Geräte in Industriehalle mit PKI-basierter Kommunikationssicherheit](https://rheintec.io/hs-fs/hubfs/iot-geraete-mit-pki-netzwerkvisualisierung-industrie.jpg?width=1456&height=816&name=iot-geraete-mit-pki-netzwerkvisualisierung-industrie.jpg)

## Example: DFN-PKI

A prominent example in German-speaking countries is the **DFN-PKI** of the German Research Network. It offers universities, research institutes and other scientific institutions the opportunity to issue digital certificates under one trustworthy umbrella. The DFN-PKI is thus a pioneer for federated, cross-organizational security structures.

## Challenges during implementation

Whether self-operated or used as a **managed PKI** - setting up a public key infrastructure requires specialist knowledge and strategic decisions. You should consider the following points:

- Choice between on-premises and cloud PKI
- Design of the certificate hierarchy (including the question: **Why two-tier PKI?**)
- Lifecycle management of certificates
- Integration into existing IT systems (e.g. Active Directory)
- Training of administrators and end users

Without clear governance, there is a risk that the PKI will become a security risk instead of a protection factor.

## Conclusion: Trust is good - PKI is better

Public Key Infrastructure is the backbone of modern, secure IT communication. It creates trust where personal interaction is no longer possible - for example in the cloud, between machines or across national borders.

If you are planning to introduce or modernize a **public key infrastructure** in your company, structured planning with clear security objectives is recommended. Whether managed internally or as a **managed PKI**: With a well thought-out PKI, you create the basis for digital trustworthiness and long-term IT security.

[Network Security & SD-WAN](https://rheintec.io/en/it-security-blog/tag/network-security-sd-wan)

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