What is Public Key Infrastructure (PKI)? In-Depth Guide

By Tibor Moes / Updated: June 2023

What is Public Key Infrastructure (PKI)? In-Depth Guide<br />

What is Public Key Infrastructure (PKI)?

In an era where digital security is paramount, Public Key Infrastructure (PKI) has become a crucial framework to ensure the safe exchange of information across the internet. Let’s dive into this fascinating world and discover how PKI secures digital communications and maintains trust in the digital realm.


  • Public Key Infrastructure (PKI) is an encryption system that ensures a safe and reliable method of exchanging data and validating identities.

  • It helps protect messages and files being sent over the internet or other networks, through the use of asymmetric encryption and digital certificates.

  • An example of PKI security is when you visit a website protected with an SSL certificate. This ensures that the data you send and receive is secure and encrypted.

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The Fundamentals of PKI

Public Key Infrastructure (PKI) is an encryption system that uses asymmetric techniques to protect messages. It also confirms the identity of the entity sending the information. To grasp the concept of PKI, one must be familiar with the hardware, software, policies, procedures, and entities associated with it, which are all necessary for securely distributing, verifying, and revoking digital certificates. The foundation of PKI lies in public cryptographic keys.

Unfortunately, security procedures of some Certificate Authorities (CAs) have been lacking, causing people to lose trust in the entire PKI system that the internet relies on. This is a major issue because a breach in one CA can put the entire PKI in danger.

To make PKI easier to understand, we can compare it to an airport, where various security checks, authorizations, and validations take place to ensure the safe and orderly flow of passengers and cargo. An essential aspect of PKI design is the Certificate Revocation List (CRL). CRLs provide a list of released certificates that should not be trusted, published by a subordinate CA if it gets compromised or needs to revoke a certificate. This safety measure helps maintain trust and security within the PKI system.

The Role of Asymmetric Encryption in PKI

Asymmetric encryption is the foundation of PKI. It’s used to secure digital messages through encryption and decryption. It employs public and private keys to ensure secure data exchange between communicating parties. The public key, which can be shared with anyone, is used to encrypt the message, while the private key, known only to the recipient, is used to decrypt it.

A primary concern with asymmetric encryption is verifying that the received public key genuinely belongs to the intended recipient. To tackle this issue, PKI relies on cryptographic algorithms such as RSA, ECC, and Diffie-Hellman to provide a secure foundation for data exchange.

By using asymmetric encryption, PKI effectively protects sensitive information from being intercepted by unauthorized parties. It establishes a secure channel for communication, enabling the safe exchange of data while maintaining privacy and integrity.

Digital Certificates: The Backbone of PKI

Digital certificates are documents that verify the identity of the owner of a public key, ensuring that the parties involved in secure communication are who they claim to be. These certificates, also known as X.509 certificates, confirm the identity of the server linked to the public key. Digital certificates play a vital role in authenticating digital identities within the PKI system.

Although digital certificates can be individually validated and automatically trusted by client software like web browsers, PKIs often need extra verification to ensure the certificates’ validity. This additional layer of trust helps maintain the integrity of the entire PKI system.

Types of Digital Certificates

There are three main types of digital certificates: SSL/TLS certificates, code signing certificates, and client certificates. SSL/TLS certificates are used to secure communication between a web server and a web browser, authenticating the website’s identity and encrypting the data sent between both parties.

Code signing certificates verify the identity of software developers and ensure that the code has not been tampered with. By confirming the code’s integrity, these certificates protect users from malicious software and enable them to trust the applications they download and use.

Client certificates, on the other hand, authenticate the identity of a user or device. These certificates verify the identity of the communicating parties and protect the data sent between them, ensuring secure and confidential communication.

Certificate Authorities (CAs): Establishing Trust

Certificate Authorities (CAs) are trusted sources that issue digital certificates, acting like digital passports to confirm the sender’s identity. CAs generate these certificates and verify the recipients’ trustworthiness before issuing them. Before distributing a digital certificate, CAs must determine the recipient’s identity, the level of trust to be placed in them, and the certificate’s type.

Although Certificate Revocation Lists (CRLs) are crucial for maintaining trust within the PKI system, certificate consumers may opt not to check them as it can slow down the authentication process. Moreover, they can decide how far back they want to go in the CA hierarchy during the check.

Organizations must be transparent if a root CA is compromised. This includes revealing details about the security breach. Root CAs have the strongest security measures, and a compromised root CA can have disastrous consequences for the entire PKI. Thus, maintaining the integrity and security of CAs is of utmost importance.

Certification Authority Hierarchy

A Certification Authority (CA) hierarchy in PKI has two levels: a Root Certificate Authority and Subordinate Certificate Authorities. Root certificates are self-signed, which means that trusting the root certificate authority is essential for any certificates leading back to it. CA hierarchies provide an extra layer of trust by issuing certificates for other CAs.

The two-tier hierarchy is necessary because the root CA must be kept offline 99.9% of the time, which is challenging for subordinate CAs that need to issue certificates regularly. This hierarchy structure allows subordinate CAs to issue certificates while maintaining the security of the root CA.

Adding more tiers to a CA hierarchy can increase the complexity of the policies and procedures governing the PKI, making its usability and scalability more challenging. Therefore, a two-tier hierarchy balances security and practicality in PKI management.

Implementing PKI: Obtaining and Managing Digital Certificates

To obtain digital certificates from a Certificate Authority (CA), you can manage them manually or use a certificate management tool. Alternatively, you can get digital certificates made and signed by a publicly trusted CA or use an in-house CA system.

Proper certificate management is crucial to ensure that certificates are valid and secure, and that the website is not an easy target for attackers. The process involves distributing certificates correctly, properly vetting and mapping them, and keeping track of all issued certificates.

Implementing a robust PKI system requires careful planning and execution, as well as continuous monitoring and management of digital certificates. This will not only maintain the integrity of the PKI, but also help protect sensitive information from potential security breaches.

Real-World Applications of PKI

PKI is essential for the Internet of Things (IoT) as it provides security, authentication, and allows for firmware updates for all connected devices. Industries such as auto manufacturers and medical device manufacturers are taking advantage of PKI for IoT devices to ensure secure connections and data exchange.

One real-world example of the importance of PKI in IoT security is the case of The Home Depot, where hackers managed to infiltrate the company’s point of sale system by sneaking onto the network disguised as an unauthenticated HVAC unit. This incident highlights the critical role of PKI in securing IoT devices and protecting sensitive data from unauthorized access.

Challenges and Risks Associated with PKI

Implementing PKI comes with challenges and risks, such as the possibility of failed audits or CA compromise. These issues could jeopardize security and affect the integrity of the entire PKI system. The biggest worry when it comes to PKI is the potential for such breaches and compromises.

A staggering 74% of organizations are unaware of how many keys and certificates they use and when they expire. Additionally, 73% of organizations have experienced certificate-related incidents in the past two years. Adding more encryption layers to meet regulatory and IT policy requirements can decrease the efficiency of business processes and raise costs.

To mitigate these challenges, organizations must invest in proper PKI management and security measures. By identifying potential risks and addressing them proactively, the integrity and trustworthiness of the PKI system can be maintained.

Best Practices for Effective PKI Management

When managing a PKI effectively, it’s crucial to plan carefully, safeguard private keys, and regularly rotate certificates. Organizations should also ensure that private keys are stored securely and access is limited. Certificate rotation, which involves replacing certificates regularly, helps reduce the risk of security breaches.

Managing PKI can be challenging, as it involves distributing certificates correctly, properly vetting and mapping them, and keeping track of all issued certificates. By adopting best practices and maintaining a proactive approach to PKI management, organizations can ensure robust deployment and minimize the risks associated with mismanagement.


In conclusion, Public Key Infrastructure (PKI) plays a vital role in securing digital communications and establishing trust in the digital world. From understanding the fundamentals of PKI to implementing robust management practices, organizations must remain vigilant in addressing potential challenges and risks associated with PKI.

By staying informed and proactive in PKI management, organizations can protect their digital assets and maintain the integrity of their PKI systems. In a world that’s increasingly interconnected, the importance of secure digital communications cannot be overstated.

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Frequently Asked Questions

Below are the most frequently asked questions.

What is meant by public key infrastructure (PKI)?

Public Key Infrastructure (PKI) is an essential tool for providing a secure environment, verifying the authenticity of digital documents, and encrypting communication for protecting data. It allows users to exchange private messages or information securely in an untrusted network.

In short, PKI is a system that ensures a safe and reliable method of exchanging data and validating identities.

What is PKI and how it works?

PKI is an authentication system that uses a pair of unique keys to secure digital exchanges. It uses public and private cryptographic keys which are linked through a certificate authority, allowing users to securely communicate with one another online.

PKI helps protect messages and files being sent over the internet or other networks.

What is the purpose of PKI?

The purpose of Public Key Infrastructure (PKI) is to provide a secure means of verifying the identity of a user or device. It does this by using cryptographic encryption that allows for authentication, encryption and digital signatures, which ensure that the data sent between two parties is protected and can be trusted as authentic.

PKI helps to protect digital information from malicious actors and preserve privacy.

What is an example of a PKI?

A great example of PKI security in action is when you visit a website protected with an SSL certificate. This ensures that the data you send and receive is secure and encrypted, allowing for safe communication between you and the site.

Author: Tibor Moes

Author: Tibor Moes

Founder & Chief Editor at SoftwareLab

Tibor has tested 39 antivirus programs and 30 VPN services, and holds a Cybersecurity Graduate Certificate from Stanford University.

He uses Norton to protect his devices, CyberGhost for his privacy, and Dashlane for his passwords.

You can find him on LinkedIn or contact him here.