Encryption at rest and in transit in HLD - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding Encryption at Rest

Which of the following best describes encryption at rest in a system?

A Data is encrypted when stored on disk or persistent storage to protect it from unauthorized access.

B Data is encrypted only when it is being sent over the network between services.

C Data is encrypted only during processing in memory to prevent leaks.

D Data is encrypted only when backed up to external storage devices.

💡 Hint

Think about when data is saved and not moving.

Encryption at rest means data is encrypted when stored on disks or databases to protect it if storage is compromised.

❓ Architecture

intermediate

Choosing Encryption Methods for Data in Transit

Which encryption method is most appropriate for securing data in transit between client and server?

A Hashing passwords before storing them in the database.

B Encrypting data backups with a symmetric key.

C TLS (Transport Layer Security) protocol to encrypt network communication.

D AES encryption applied directly to stored files on the server.

💡 Hint

Consider how data moves between devices over the network.

TLS encrypts data as it travels over the network, protecting it from eavesdropping or tampering.

❓ scaling

advanced

Scaling Encryption Key Management

In a large distributed system with thousands of servers, what is the best practice to manage encryption keys for data at rest?

A Store all encryption keys locally on each server to reduce network latency.

B Use a centralized key management service (KMS) that securely stores and rotates keys.

C Hardcode encryption keys in application code for easy access.

D Generate new keys randomly on each server without sharing.

💡 Hint

Think about security and ease of key rotation across many servers.

A centralized KMS allows secure storage, controlled access, and automated key rotation, which is critical at scale.

❓ tradeoff

advanced

Tradeoffs Between Encryption Performance and Security

Which statement best describes a common tradeoff when implementing encryption at rest and in transit?

A Stronger encryption algorithms always improve performance but reduce security.

B Encryption at rest eliminates the need for encryption in transit.

C Using no encryption improves security by avoiding key management complexity.

D Encrypting data increases CPU usage and latency but improves data confidentiality.

💡 Hint

Consider how encryption affects system resources and speed.

Encryption requires extra processing, which can slow down systems, but it protects data from unauthorized access.

❓ estimation

expert

Estimating Impact of Encryption on System Throughput

A web service processes 10,000 requests per second. Enabling TLS encryption adds 5ms latency per request due to handshake and encryption overhead. What is the approximate maximum throughput (requests per second) after enabling TLS?

A About 2,000 requests per second

B About 200 requests per second

C About 5,000 requests per second

D About 10,000 requests per second

💡 Hint

Calculate how added latency affects requests per second capacity.

Each request now takes 5ms longer. Since 1 second = 1000ms, max requests = 1000ms / 5ms = 200 requests per thread. But original throughput was 10,000 req/s, so system likely has concurrency. Assuming linear scaling, throughput reduces roughly by factor of 5ms added latency.