Cryptography Background Questions
Experience working with cryptographic algorithms, protocols, and secure design practices. Candidates should describe algorithms and protocols they have used or implemented, threat modeling and key management experience, compliance considerations, and concrete projects that demonstrate applied cryptography knowledge and practical trade offs.
HardTechnical
28 practiced
Design a protocol allowing multiple parties to compute aggregated statistics (sums, averages) without revealing raw inputs using MPC or homomorphic encryption. Define a clear threat model (honest-but-curious vs malicious), communication rounds, resilience to dropouts, and practical scalability considerations (bandwidth, CPU).
EasyTechnical
34 practiced
Describe the cryptographic goals and message flow of a modern TLS handshake (e.g., TLS 1.2 or TLS 1.3). Explain how confidentiality, integrity, authentication, and (where applicable) perfect forward secrecy are achieved. Mention the role of certificates, key exchange, and session key derivation.
EasyTechnical
32 practiced
What is Perfect Forward Secrecy (PFS)? Explain how PFS prevents retroactive decryption after a long-term key compromise, which protocols provide PFS by default, and situations where PFS might be impractical to use.
MediumTechnical
27 practiced
You see application logs and network traces that suggest an exponent-related side-channel leak (responses vary with input patterns). Describe how you would analyze the logs to confirm a leak, what experiments you would run to reproduce the leak in lab, and immediate/long-term mitigations to protect the private key.
MediumTechnical
27 practiced
Perform a threat model for a client-side end-to-end encrypted (E2EE) messaging app. Specify the adversary capabilities (network attacker, compromised server, compromised client), assets, trust boundaries, and design decisions for key generation, storage, forward secrecy, message replay protection, and metadata minimization. State assumptions and how they affect design.
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