Secret Key Encryption

Question 1

What is ECB Mode?

Answer 1

Encrypts each block independently. Same input block → same output. Weak: patterns are preserved.

Not recommended for secure use.

Question 2

What is CBC Mode?

Answer 2

Uses IV to encrypt the first block. Each block is XORed with previous ciphertext. Breaks repetition → better security.

One change = ripple through ciphertext.

Question 3

What are CFB, OFB, and CTR modes?

Answer 3

CFB: Feedback mode using IV and XOR. OFB: Similar to CFB, turns block cipher into stream. CTR: Uses a counter + nonce to encrypt (parallelizable).

Question 4

What are deterministic modes?

Answer 4

Always same result for same plaintext: ✅ ECB (bad) ❌ CBC, CFB, OFB, CTR (use random IVs or counters).

Question 5

What is the Skipjack Cipher?

Answer 5

Developed by NSA. 80-bit key. Operates on 64-bit blocks.

Less secure by today’s standards.

Question 6

How many rounds does AES have based on key size?

Answer 6

128-bit key → 🔁 10 rounds. 192-bit key → 🔁 12 rounds. 256-bit key → 🔁 14 rounds.

More key = more transformation rounds.