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What is Public Key Infrastructure (PKI)?| Cybersecurity Interview Questions and Answers| Security

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Technology

Summary: What is PKI (Public Key Infrastructure)?

PKI (Public Key Infrastructure) is an underlying framework that enables secure information exchange between parties that may not know or trust each other beforehand. It uses digital certificates to authenticate identities of users and servers.

Key Concepts / Components

Digital Certificate (Passport/Driver’s License Analogy)

  • Acts like proof of identity in the digital world.
  • Authenticates the identity of the entity associated with the certificate.
  • Uses the X.509 standard.
  • Contains a copy of the entity’s public key.

Certificate Authority (CA)

  • A trusted third party that:
    • verifies identities
    • then issues and revokes digital certificates
  • Examples mentioned: DigiCert, GoDaddy.

Registration Authority (RA)

  • Helps the CA with identity verification.
  • Does not directly issue certificates (as noted in the subtitles).

Certificate Issuing / Enrollment Process (CSR-based)

  1. A requester (user or server) creates a CSR (Certificate Signing Request).
  2. The CSR includes:
    • requester identifying details (e.g., name, server name, email)
    • the requester’s public key
  3. The requester sends the CSR to a CA of their choice.
  4. The CA validates the requester identity (may request more data if needed).
  5. If validated, the CA:
    • places the requester’s public key and identity info into an X.509 certificate
    • digitally signs the certificate using the CA’s private key
  6. The requester receives the signed certificate and can distribute it to others.
  7. The certificate includes an expiration/expiry date.

Certificate Revocation (When certificates should no longer be trusted)

Revocation may be needed if:

  • the certificate expires, or
  • the requester’s private key is compromised

Two revocation methods highlighted are:

  1. CRL (Certificate Revocation List)

    • Lists revoked certificates by serial number
    • Drawbacks mentioned: time delay and higher bandwidth usage

  2. OCSP (Online Certificate Status Protocol)

    • Provides real-time status checks
    • Responds with whether the certificate is valid / invalid / unknown

Main Speakers / Sources (from subtitles)

  • Main speaker/channel name: “separate platter” (as in “welcome to separate platter”).
  • Sources mentioned:
    • CA examples: DigiCert, GoDaddy
    • Standards/protocols: X.509, CSR, CRL, OCSP

Original video