CA TLS mTLS Interview Questions

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Basic Understanding

  1. What is TLS and how does it differ from SSL?
    • Answer: TLS is the successor to SSL. Both are cryptographic protocols designed for secure communication over a network. TLS provides improved security and efficiency. The key differences include stronger encryption algorithms in TLS and the deprecation of some vulnerable features that were part of SSL.
  2. Can you explain the TLS handshake process?
    • Answer: The TLS handshake involves several steps:
      1. Client and server establish a connection.
      2. The server sends its certificate to the client.
      3. The client verifies the server’s certificate.
      4. Key exchange, where the client and server agree on session keys for encryption and decryption.
      5. Final handshake messages are sent to confirm the encrypted session is starting.
  3. What is a Certificate Authority (CA)?
    • Answer: A Certificate Authority is an entity that issues digital certificates. These certificates verify the ownership of a public key by the named subject of the certificate, ensuring secure communication over networks.

Intermediate Knowledge

  1. How does mutual TLS (mTLS) differ from TLS?
    • Answer: In TLS, only the server is authenticated by the client. mTLS extends this by also requiring the client to authenticate itself to the server, providing bidirectional authentication.
  2. What are self-signed certificates and what are their pros and cons?
    • Answer: Self-signed certificates are issued by the entity itself, not by a CA. Pros include cost-effectiveness and ease of setup. Cons involve trust issues, as they are not verified by a third party, and potential security vulnerabilities.
  3. Can you explain certificate pinning?
    • Answer: Certificate pinning is the process of associating a host with their expected certificate or public key. By doing so, it prevents attackers from using forged certificates to intercept secure communications.

Advanced Understanding

  1. How do you implement mTLS in a microservices architecture?
    • Answer: Implementing mTLS in microservices involves configuring both client and server services to mutually authenticate using TLS certificates. This often includes setting up a private CA to manage the certificates and configuring each service with a unique client certificate.
  2. What are the common vulnerabilities associated with TLS and how can they be mitigated?
    • Answer: Common TLS vulnerabilities include attacks like POODLE, BEAST, and CRIME. Mitigation strategies include using the latest TLS protocol versions, avoiding weak ciphers, and regular updates of TLS libraries.
  3. How would you securely manage and store TLS certificates in a large organization?
    • Answer: Best practices include using a centralized certificate management system, enforcing strong access controls, regularly rotating certificates, and automating the renewal process to avoid expirations.
  4. Can you discuss any experience you have with certificate transparency logs?
    • Answer: Certificate transparency logs are public, auditable records of certificates issued by CAs. My experience includes monitoring these logs to verify that no unauthorized certificates have been issued for our domains.

Scenario-Based Questions

  1. If a client fails to establish a TLS connection with your server, what steps would you take to troubleshoot the issue?
    • Answer: I would start by checking the server’s TLS configuration and certificate status. Then, I would verify network accessibility and firewall settings. If the issue persists, I would use tools like Wireshark to analyze the handshake process and pinpoint the failure.
  2. How would you respond to a certificate expiration incident on a critical production server?
    • Answer: Immediately, I would renew or replace the expired certificate and restart the service. For long-term measures, I would implement certificate expiration monitoring and alerts to prevent future occurrences.