6 exercises — AES, key, block cipher, stream cipher, modes of operation, RSA, public/private keys, elliptic curves, and hybrid encryption.
0 / 6 completed
1 / 6
Which term correctly describes AES: encrypting and decrypting data using the SAME shared key on both sides?
Symmetric encryption uses one shared secret key for both encryption and decryption. AES (Advanced Encryption Standard) is the dominant symmetric cipher today — fast, well-tested, and used for bulk data encryption (disks, TLS session data, file encryption).
Key vocabulary: • Key: the secret value that controls encryption/decryption • Block cipher: encrypts data in fixed-size chunks (AES uses 128-bit blocks) • Stream cipher: encrypts data one bit/byte at a time (e.g. ChaCha20)
Contrast with asymmetric encryption (RSA, ECC), which uses a mathematically linked key pair — a public key and a private key — instead of one shared secret.
2 / 6
What does "mode of operation" mean in the context of a block cipher like AES (e.g. CBC, GCM, CTR)?
A mode of operation defines how a block cipher (which only encrypts one fixed-size block at a time) is applied repeatedly to encrypt data of arbitrary length, and how blocks relate to each other.
Common modes: • CBC (Cipher Block Chaining): each block is XORed with the previous ciphertext block before encryption — requires padding, no built-in integrity check • GCM (Galois/Counter Mode): combines encryption with a built-in authentication tag (AEAD — Authenticated Encryption with Associated Data); the modern default for TLS • CTR (Counter Mode): turns a block cipher into a stream cipher by encrypting an incrementing counter — parallelisable, no padding needed
Using ECB mode (no chaining at all) is considered a mistake in production — identical plaintext blocks produce identical ciphertext blocks, leaking patterns.
3 / 6
In RSA, which term describes "the half of the key pair you keep secret and never share with anyone"?
The private key is never shared. The public key is the opposite — it is distributed freely and used by others to encrypt data for you, or to verify signatures you created with your private key.
Key-pair vocabulary: • Key pair: the mathematically linked public + private key generated together • Key generation: the process of creating a new key pair (e.g. openssl genrsa, ssh-keygen) • Key exchange: the process of two parties agreeing on a shared secret without transmitting it directly (RSA key transport, or Diffie-Hellman)
Rule to remember: "Public key encrypts / verifies. Private key decrypts / signs." — this is the reverse of what many beginners assume.
4 / 6
Complete the sentence: "RSA is used for key exchange; AES is used for bulk data encryption. Together they form ___"
Hybrid encryption is the standard real-world pattern because asymmetric encryption (RSA, ECC) is computationally expensive and impractical for large amounts of data, while symmetric encryption (AES) is fast but requires a shared secret both sides already know.
The pattern: 1. The two parties use asymmetric cryptography (RSA key transport, or a Diffie-Hellman key exchange) to securely agree on a random symmetric key 2. That symmetric key — often called a session key — then encrypts the actual data using AES
This is exactly how TLS works: the handshake establishes a session key using asymmetric operations, then all application data is encrypted with fast symmetric AES-GCM using that session key.
5 / 6
Why is Elliptic Curve Cryptography (ECC, e.g. Curve25519, P-256) often preferred over RSA for the same security level?
The core selling point of elliptic curve cryptography is efficiency at equivalent security. Because the underlying math problem (the elliptic curve discrete logarithm problem) is harder to solve than RSA's integer factorisation problem per bit of key length, ECC needs far smaller keys for the same strength.
Vocabulary: • Curve: the specific elliptic curve used (P-256, P-384 — NIST curves; Curve25519 — a modern, widely trusted alternative) • ECDSA: Elliptic Curve Digital Signature Algorithm — used for signing (e.g. certificate signatures) • ECDH: Elliptic Curve Diffie-Hellman — used for key exchange
Smaller keys mean less data to transmit in a TLS handshake and faster cryptographic operations — one reason modern TLS 1.3 favours ECDHE key exchange.
6 / 6
Which statement correctly describes the trade-off between key size, computational cost, and quantum resistance?
This is a nuanced but important distinction in modern security vocabulary:
• Key size vs. computational cost: larger keys generally mean more computation per operation (more CPU time to encrypt/decrypt/sign), which is why algorithm and key-size choices always balance security against performance • Quantum resistance: Shor's algorithm, if run on a sufficiently powerful quantum computer, could efficiently break RSA and ECC regardless of key size, because it solves the underlying factorisation/discrete-log problems directly • Symmetric algorithms like AES are considered comparatively quantum-resistant already (Grover's algorithm only halves the effective key strength, so AES-256 remains strong)
This is why NIST has standardised post-quantum cryptography (PQC) algorithms (e.g. CRYSTALS-Kyber, ML-KEM) designed to resist quantum attacks — a distinct category from simply "using a bigger RSA key."
What does the "Symmetric & Asymmetric Vocabulary — Cryptography & PKI Exercises" exercise cover?
Practise the core vocabulary of symmetric encryption (AES, block/stream ciphers, modes of operation) and asymmetric encryption (RSA, key pairs, ECC). Beginner exercises for developers.
Is this exercise free to use?
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How many questions are in "Symmetric & Asymmetric Vocabulary — Cryptography & PKI Exercises"?
This exercise has 6 questions. Each one gives instant feedback with an explanation, so you can see exactly why an answer is right or wrong.
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Articles explain vocabulary and concepts through prose, while exercises like this one are interactive drills -- multiple-choice questions -- that test and reinforce your recall of specific terms and phrasing.
Can I retry this exercise?
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Where can I find more Cryptography & PKI exercises?
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Is this exercise suitable for beginners?
This exercise assumes basic familiarity with IT terminology. If a term feels unfamiliar, check the site Glossary for a plain-English definition before attempting the questions.
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