AES Key Schedule
The AES key schedule expands an N-bit master key into (rounds + 1) round keys of 128 bits each, one consumed by every AddRoundKey.
Purpose
It supplies each round with an independent round key, achieving key confusion and separation between rounds.
Mechanism
The master key is arranged as 4-byte words and expanded iteratively: every fourth word derives from RotWord, SubWord, and an XOR with Rcon, then XORs into the previous word to form the new word. A 128-bit key expands into 44 32-bit words (11 round keys).
Use cases
- AES encryption preprocessing
- Inverted round keys for AES decryption
- Round-key generation