End-to-end encryption concept in HLD - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

What is the primary benefit of end-to-end encryption in messaging systems?

Consider a messaging app where messages are encrypted from sender to receiver without intermediaries decrypting them.

What is the main advantage of this approach?

A Messages are stored unencrypted on the server for faster retrieval.

B Encryption keys are shared with the server to allow message indexing.

C Only the sender and receiver can read the messages, preventing servers from accessing the content.

D Messages are encrypted only during transmission but decrypted on the server.

💡 Hint

Think about who can read the message content in end-to-end encryption.

End-to-end encryption ensures that only the sender and receiver hold the keys to decrypt messages. Servers cannot read the content, enhancing privacy.

❓ Architecture

intermediate

Which component is responsible for encrypting messages in an end-to-end encrypted chat app?

In an end-to-end encrypted chat system, where should the encryption of messages happen?

A On the server after receiving the message.

B On the sender's device before sending the message.

C On the receiver's device after receiving the message.

D On a proxy server between sender and receiver.

💡 Hint

Encryption must happen before the message leaves the sender's control.

Encryption must occur on the sender's device so that the message is protected before it travels through any servers or networks.

❓ scaling

advanced

How does end-to-end encryption affect server scalability in a messaging platform?

End-to-end encryption means servers cannot read message content. What is a key impact on server scalability?

A Servers store encryption keys to speed up message delivery.

B Servers must decrypt and re-encrypt messages, increasing CPU usage significantly.

C Servers can compress messages more efficiently due to encryption.

D Servers cannot perform content-based filtering or indexing, reducing processing load but limiting features.

💡 Hint

Think about what servers cannot do if they cannot read message content.

Since servers cannot read encrypted messages, they cannot filter or index content, which reduces processing but limits features like search or moderation.

❓ tradeoff

advanced

What is a common tradeoff when implementing end-to-end encryption in communication apps?

End-to-end encryption improves privacy but introduces challenges. Which is a typical tradeoff?

A Limited ability for the server to provide features like message search or spam filtering.

B Increased risk of server data breaches exposing message content.

C Simplified key management by storing keys on the server.

D Reduced message delivery speed due to server decryption overhead.

💡 Hint

Consider what features require server access to message content.

Because servers cannot decrypt messages, features like search, spam filtering, or content moderation become difficult or impossible to implement.

❓ estimation

expert

Estimate the additional latency introduced by end-to-end encryption in a messaging app compared to unencrypted messaging.

Assume encryption and decryption each take 5 milliseconds on client devices. Network latency is 50 milliseconds one-way. What is the approximate total message round-trip latency with end-to-end encryption?

A 120 milliseconds

B 70 milliseconds

C 110 milliseconds

D 60 milliseconds

💡 Hint

Calculate encryption + network + decryption times for both sender and receiver.

Encryption on sender: 5ms, network to server: 50ms, network to receiver: 50ms, decryption on receiver: 5ms. Total = 5 + 50 + 50 + 5 = 110ms. But message round-trip includes sender receiving acknowledgment, adding another 10ms encryption/decryption overhead, totaling about 120ms.