Cryptography -- Practice Problems
Cryptography — Practice Problems
10 MCQ questions covering symmetric/asymmetric encryption, AES, RSA, hash functions, digital signatures, key exchange, and post-quantum cryptography. Select an option to check your answer.
Intuition
A lock and key system for digital messages: Cryptography is like a postal security system, symmetric encryption is a shared lock (both sender and key have the same key), asymmetric encryption is a mailbox (anyone can drop mail in, only you can open it), and hash functions are tamper-evident seals.
Why it matters: Every online transaction, password login, and secure message relies on cryptography. Understanding it explains why HTTPS matters, how Bitcoin works, and why quantum computers threaten current security.
The key insight: Security depends on mathematical hardness assumptions, RSA relies on factoring being hard, Diffie-Hellman on discrete logarithms, and when those assumptions break, so does the security.
Symmetric Encryption and Block Cipher Modes
Asymmetric Encryption, Hash Functions, and Key Exchange
Additional Cryptography Questions
Common Mistakes
Confusing encryption with signing: Encryption protects confidentiality (only recipient can read). Signing provides authentication and integrity (sender can’t deny sending). Don’t use them interchangeably.
Assuming longer keys are always better: Security depends on the algorithm, not just key length. A 1024-bit RSA key is less secure than a 256-bit ECC key. Don’t assume key length alone determines security.
Forgetting that hash functions are not encryption: Hash functions produce fixed-size digests from arbitrary input. They’re one-way (can’t recover input). Don’t use them for encryption.