gen-define-the-aes-block-cipher-and-give-one-short-worked-exampl-d3e8

Define the AES block cipher and give one short worked example.

# AES Block Cipher ## Definition **AES (Advanced Encryption Standard)** is a symmetric block cipher that: - Operates on **128-bit blocks** (16 bytes) - Uses key sizes of **128, 192, or 256 bits** - Performs **10, 12, or 14 rounds** (depending on key size) - Uses a substitution-permutation network structure ### Main Operations (per round): 1. **SubBytes** - Non-linear byte substitution using S-box 2. **ShiftRows** - Cyclically shift rows of the state array 3. **MixColumns** - Mix data within each column (skipped in final round) 4. **AddRoundKey** - XOR state with round key --- ## Worked Example (Simplified) **AES-128 encryption of a single block:** **Input:** - Plaintext: `00 11 22 33 44 55 66 77 88 99 aa bb cc dd ee ff` (hex) - Key: `00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f` (hex) **Process:** 1. Arrange plaintext into 4×4 state matrix (column-major) 2. Initial AddRoundKey (XOR with key) 3. Perform 10 rounds of transformations 4. Extract ciphertext from final state **Output:** - Ciphertext: `69 c4 e0 d8 6a 7b 04 30 d8 cd b7 80 70 b4 c5 5a` (hex) This can be verified using standard AES test vectors or libraries like OpenSSL.