Public Key Infrastructure(PKI) in Network Security

 

Public Key Infrastructure(PKI)

Public Key Infrastructure (PKI) is a framework used to create, manage, distribute, verify, and revoke digital certificates and public keys.

PKI enables secure communication by providing:
  • Authentication
  • Data Integrity
  • Trust

It is commonly used over open networks such as the Internet.

Need for PKI
Public-key cryptography allows public keys to be shared openly. However, it does not by itself guarantee that a public key actually belongs to the claimed user.

PKI solves this problem by:
  • Verifying user identities.
  • Binding public keys with identities using digital certificates.
  • Establishing trust through trusted authorities.

Without PKI, systems may be vulnerable to Man-in-the-Middle (MITM) attacks.


Components of PKI

1. Certificate Authority (CA)
The Certificate Authority (CA) is a trusted entity in PKI that:

  • Issues digital certificates.
  • Digitally signs certificates.
  • Revokes certificates when they are compromised or expired.

CA acts as the root of trust in PKI.


2. Registration Authority (RA)
The Registration Authority (RA) assists the CA by:

  • Verifying the identity of users.
  • Approving or rejecting certificate requests.
  • Forwarding verified requests to the CA.

RA does not issue certificates.


3. Digital Certificate
A Digital Certificate, usually based on X.509, is used to:

  • Bind a public key with the identity of its owner.
  • Provide a certificate digitally signed by the CA.
  • Support authentication and secure communication. 

4. Certificate Repository

  • Stores issued certificates.
  • Allows users to retrieve and verify certificates

5. Certificate Revocation System
This system ensures that invalid or revoked certificates are not trusted.
Two commonly used mechanisms are:

CRL – Certificate Revocation List
A list containing certificates that have been revoked.

OCSP – Online Certificate Status Protocol
A protocol used to determine the revocation status of a digital certificate.


Working of PKI

User / Server
(Requests Certificate)
        ↓
Registration Authority (RA)
(Identity Verification)
        ↓
Certificate Authority (CA)
(Issues & Signs Certificate)
        ↓
Certificate Repository
        ↓
Client / Browser
(Verifies Certificate)

Steps
  1. The user or server requests a certificate.
  2. The RA verifies the identity.
  3. The verified request is forwarded to the CA.
  4. The CA issues and digitally signs the certificate.
  5. The certificate is stored in the certificate repository.
  6. A client or browser retrieves and verifies the certificate. 

Applications of PKI

  • HTTPS and SSL/TLS
  • Secure email systems
  • VPN authentication
  • Digital signatures
  • Software and code signing

Handwritten Notes- Download PDF

Video Explanation-Watch on YouTube

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