Cryptographic Primitives

Question 1

Give the 3 security properties of a hash function (D‑P‑S).

Answer 1

Determinism, Pre‑image resistance, Second pre‑image (collision) resistance.

Question 2

One‑line definition of symmetric encryption.

Answer 2

Encrypt and decrypt with the same secret key shared by sender and receiver.

Question 3

Symmetric encryption: 1 pro & 1 con.

Answer 3

Pro: very fast; Con: secure key exchange required.

Question 4

One‑line definition of asymmetric encryption.

Answer 4

Encrypt with a public key, decrypt with the corresponding private key.

Question 5

Asymmetric encryption: 1 pro & 1 con.

Answer 5

Pro: no pre‑shared secret; Con: slower, needs public‑key authentication to avoid MITM.

Question 6

Hybrid crypto example used on the web.

Answer 6

TLS/HTTPS — public key sets up a symmetric session key; bulk data encrypted symmetrically.

Question 7

Three guarantees of a digital signature.

Answer 7

Authentication, Integrity, Non‑repudiation.

Question 8

Four steps to sign & verify a message.

Answer 8

Hash → Sign with private key → Send message+signature → Receiver hash & verify with public key.

Question 9

Does a digital signature provide confidentiality?

Answer 9

No — it proves origin and integrity but does not hide the message contents.

Question 10

Why is SHA‑256 stronger than MD5?

Answer 10

SHA‑256 collision attacks are still infeasible; MD5 collisions found quickly on standard hardware.