Top Ten Interview Questions on Public Key Infrastructure (PKI) Asked at Meta
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Public Key Infrastructure (PKI) plays a crucial role in securing digital communications. For tech roles at Meta, understanding PKI is essential. Here are the top ten interview questions commonly asked at Meta about PKI, along with detailed answers.
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1. What is Public Key Infrastructure (PKI), and why is it important?
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Public Key Infrastructure (PKI) is a framework that manages keys and digital certificates to secure communications over the internet. It uses asymmetric cryptography with public and private keys to ensure confidentiality, integrity, authentication, and non-repudiation of data. PKI is essential because it establishes trust in digital environments, enabling secure transactions, communications, and access control.
2. Can you explain the difference between symmetric and asymmetric encryption?
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Symmetric encryption uses the same key for both encryption and decryption, making it faster but less secure when key management is weak. Asymmetric encryption, on the other hand, uses two different keys: a public key for encryption and a private key for decryption. PKI relies on asymmetric encryption for secure communications, as it allows secure key exchange without revealing private keys.
3. How does a digital certificate work in PKI?
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A digital certificate is an electronic document used to prove the ownership of a public key. In PKI, a trusted Certificate Authority (CA) issues certificates after verifying the identity of the entity requesting it. The certificate contains the public key, the entity’s identity, and the CA’s digital signature. The certificate ensures that the public key belongs to the verified entity and is used to establish trust in digital transactions.
4. What is a Certificate Authority (CA) and what role does it play in PKI?
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A Certificate Authority (CA) is a trusted entity that issues digital certificates in a PKI environment. The CA verifies the identity of the certificate requester and digitally signs the certificate, linking the identity to a public key. The CA’s signature ensures that the public key belongs to the certified entity. If a CA is trusted, the certificates it issues are trusted, forming the foundation of trust in PKI.
5. What is the difference between a root CA and an intermediate CA?
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A root CA is the top-level authority in a PKI hierarchy. Its certificate is self-signed, and it is the ultimate trust anchor. An intermediate CA is subordinate to the root CA and is used to distribute the trust across multiple entities. By using intermediate CAs, organizations can limit the exposure of the root CA and maintain security by keeping the root offline and using intermediates for day-to-day certificate issuance.
6. How does a Certificate Revocation List (CRL) work?
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A Certificate Revocation List (CRL) is a list of digital certificates that have been revoked by the CA before their expiration date. CRLs are distributed to notify users that specific certificates should no longer be trusted. Certificates can be revoked for various reasons, including compromise of the private key or a change in the entity’s status. Applications verify certificates by checking the CRL to ensure the certificate is still valid.
7. What is the Online Certificate Status Protocol (OCSP), and how does it differ from CRL?
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The Online Certificate Status Protocol (OCSP) is a real-time protocol used to check the status of a digital certificate. Unlike a CRL, which requires downloading an entire list of revoked certificates, OCSP allows clients to query the CA for the status of a specific certificate. This makes OCSP faster and more efficient, as it only provides information about the queried certificate rather than the entire list of revoked ones.
8. How is PKI used in securing HTTPS communications?
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In HTTPS communications, PKI is used to establish a secure connection between a web server and a browser. The web server presents its digital certificate, which contains its public key, to the browser. The browser validates the certificate through the CA’s digital signature and uses the server’s public key to encrypt a session key. The server then decrypts the session key with its private key, allowing secure communication using symmetric encryption for the rest of the session.
9. What is key escrow, and when is it used in PKI?
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Key escrow is a security measure where cryptographic keys are stored by a trusted third party, called the escrow agent. This ensures that encrypted data can be decrypted if the original key is lost or becomes inaccessible. In PKI, key escrow is often used in organizations to ensure that important encrypted data can be recovered if an employee leaves or a key is compromised. However, it introduces risks if the escrow agent is compromised.
10. How can PKI be scaled to support large organizations?
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Scaling PKI in large organizations involves distributing certificate issuance across multiple intermediate CAs and automating the certificate lifecycle management process. Organizations can use tools for automated certificate provisioning, renewal, and revocation. Load balancing and clustering of CA services can also enhance scalability. Additionally, organizations must maintain robust key management policies to avoid bottlenecks and ensure security across multiple layers of the infrastructure.
In conclusion, these top PKI interview questions highlight the importance of understanding how Public Key Infrastructure supports digital security. By mastering these topics, candidates can demonstrate their knowledge and preparedness for engineering roles at Meta or any other tech company requiring expertise in PKI.
