What is PKI and why is it important?

PKI (Public Key Infrastructure) is a framework of technologies, policies, and procedures that enables secure digital communications through encryption and authentication. It's the foundation that makes SSL/TLS certificates, digital signatures, and secure email possible.

What are the main components of PKI?

The main components are: Certificate Authority (CA) that issues certificates, Registration Authority (RA) that verifies identities, digital certificates that bind public keys to identities, public/private key pairs for encryption, and Certificate Revocation Lists (CRLs) or OCSP for checking certificate status.

How does PKI enable SSL certificates to work?

PKI provides the trust framework for SSL certificates. A Certificate Authority verifies your identity, issues a certificate binding your public key to your domain, and signs it with their private key. Browsers trust this chain because root CA certificates are pre-installed in their trust stores.

What is the difference between public and private keys?

Public keys can be shared freely and are used to encrypt data or verify signatures. Private keys must be kept secret and are used to decrypt data or create signatures. Together, they form a key pair where data encrypted with one can only be decrypted with the other.

What is a Certificate Revocation List (CRL)?

A CRL is a list published by a Certificate Authority containing certificates that have been revoked before their expiration date. Browsers and applications check CRLs to ensure certificates haven't been compromised or invalidated.

What is OCSP and how does it differ from CRL?

OCSP (Online Certificate Status Protocol) is a real-time method to check if a certificate is revoked. Unlike CRLs which are periodically downloaded lists, OCSP queries the CA directly for a specific certificate's status, providing more current information with less bandwidth.

Can I run my own PKI for my organization?

Yes, organizations can run private PKI for internal use cases like employee authentication, device certificates, and internal services. However, for public-facing websites, you need certificates from publicly trusted CAs that browsers recognize.

What is a certificate chain or chain of trust?

A certificate chain is a hierarchy of certificates from your end-entity certificate up to a trusted root CA. Each certificate is signed by the one above it. Browsers verify this chain to establish trust, with root CA certificates being pre-trusted in the browser's certificate store.

How does PKI protect against man-in-the-middle attacks?

PKI protects against MITM attacks by requiring servers to prove their identity with a certificate signed by a trusted CA. An attacker can't forge a valid certificate for a domain they don't control, so browsers will show security warnings if someone tries to intercept the connection.

What is PKI (Public Key Infrastructure)? Complete Guide

Q: What is a Certificate Authority (CA)?

A Certificate Authority is a trusted organization that issues, manages, and revokes digital certificates. CAs verify the identity of certificate requesters before issuing certificates. Examples include DigiCert, Sectigo, Let's Encrypt, and GlobalSign.

Understanding PKI

Public Key Infrastructure (PKI) is a comprehensive framework of technologies, policies, and procedures that create, manage, distribute, use, store, and revoke digital certificates and manage public-key encryption. PKI is the foundation that enables SSL/TLS certificates to work securely, as defined inRFC 5280.

Public Key Cryptography

Uses mathematical algorithms with two related keys: a public key for encryption and a private key for decryption. This asymmetric approach solves the key distribution problem.

Digital Certificates

Digital documents (X.509 format) that bind public keys to identities, verified by trusted Certificate Authorities (CAs). They enable authentication and trust.

Why PKI Matters for Web Security

Every time you see the padlock icon in your browser, PKI is working behind the scenes. Without PKI, there would be no way to verify that a website is legitimate or to encrypt your communications securely.

PKI Powers These Technologies

HTTPS/SSL/TLS certificates
S/MIME email encryption
Code signing certificates
Document signing

VPN authentication
Smart card authentication
IoT device security
API security

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Key Components of PKI

Certificate Authority (CA)

The trusted entity that issues, manages, and revokes digital certificates. CAs verify the identity of certificate requesters before issuing certificates.

Examples: DigiCert, Sectigo, Let's Encrypt, GlobalSign

Registration Authority (RA)

Acts as a liaison between users and the CA, handling certificate requests and verification processes on behalf of the CA.

In many cases, the CA also performs RA functions directly.

Public/Private Key Pairs

Mathematically related keys where data encrypted with one can only be decrypted with the other. The public key is shared; the private key is kept secret.

Common algorithms: RSA (2048/4096-bit), ECDSA (P-256, P-384)

Digital Certificates (X.509)

Electronic documents that bind a public key to an identity (domain, organization, or individual). They contain the subject's information, public key, CA signature, and validity period.

Learn about certificate types →

Certificate Revocation (CRL & OCSP)

Mechanisms to check if a certificate has been revoked before expiration. CRLs are periodically published lists; OCSP provides real-time status checks.

OCSP Stapling improves performance by having the server provide the status.

How PKI Works: Step by Step

Certificate Lifecycle

Key Pair Generation

User/server generates a public-private key pair using RSA or ECDSA algorithm

Certificate Signing Request (CSR)

Create a CSR containing the public key and identity information, signed with the private key

Identity Verification

CA validates domain ownership (DV), organization identity (OV), or extended validation (EV)

Certificate Issuance

CA creates the certificate binding identity to public key, signs it with CA's private key

Installation & Use

Certificate installed on server; browsers verify chain of trust to root CA

Renewal or Revocation

Certificate renewed before expiration or revoked if compromised/no longer needed

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The Chain of Trust

PKI establishes trust through a hierarchical chain. Each certificate is signed by a higher-level certificate, ultimately leading to a root CA that browsers trust implicitly.

Root Certificate

Self-signed, pre-installed in browsers/OS trust stores

Implicitly Trusted

Intermediate Certificate

Signed by root, issues end-entity certificates

Chain Link

End-Entity (Your Certificate)

Your SSL/TLS certificate for your domain

Your Certificate

PKI in Practice: Real-World Examples

Website Security (HTTPS)

When you visit my-ssl.com, your browser verifies our SSL certificate was issued by a trusted CA, establishing an encrypted connection.

Check any website's SSL →

Code Signing

Software developers sign their applications so users can verify the software hasn't been tampered with and comes from a legitimate source.

Learn about code signing →

Email Encryption (S/MIME)

S/MIME certificates enable email encryption and digital signatures, protecting sensitive business communications.

Learn about email certificates →

Enterprise Authentication

Organizations use PKI for VPN access, smart card login, Wi-Fi authentication, and securing internal services.

Explore enterprise certificates →

Benefits of PKI Implementation

Enhanced Security

Strong encryption and authentication protect against cyber threats

Compliance

Meet regulatory requirements for data protection (GDPR, PCI-DSS, HIPAA)

Scalability

Centralized management of certificates across large organizations

What is PKI (Public Key Infrastructure)?