Key Schedule
A key schedule is the algorithm that derives multiple round keys from the master key, the preprocessing stage of a block cipher.
Purpose
It supplies an independent round key to each round, achieving key diffusion and confusion across rounds.
Mechanism
Round keys are derived iteratively from the master key: each round applies shifts, substitutions, constant XORs, and similar operations to the previous round key to produce the next. AES, DES, and Blowfish each use a different expansion scheme.
Use cases
- AES/DES key expansion
- Blowfish P-array/S-box initialization
- Round-key generation