AES Round Function
The AES round function is the set of four transformations applied to the 16-byte state in each round: SubBytes, ShiftRows, MixColumns, and AddRoundKey.
Purpose
Its composition of nonlinear substitution, row shifting, column mixing, and key addition delivers confusion and diffusion, forming the core of AES security.
Mechanism
SubBytes replaces each byte nonlinearly via the S-box; ShiftRows rotates the rows cyclically; MixColumns mixes columns over GF(2^8); AddRoundKey XORs the round key. A 128-bit key runs 10 rounds, a 256-bit key 14 rounds.
Use cases
- Core of AES encryption
- Inverted round function for AES decryption
- Cryptography teaching