In the Rijndael cipher, the initial Key Addition input is the Cipher Key itself. Key Expansion Unit Cycle Time the time to generate one subkey for a round. Required to be at least as fast as the round encryption cycle time, however, depending on how fast, this will also determine how the RAM is used for storage. Key Setup Time Overhead time required to set up and load the key register. A full pipelined architecture will be used.
Registers hold each subkey for the matching encryption unit.
The key expansion unit involves generating each subkey in time for each subkey register. Several factors of the unit configuration need to be further refined to finalize the architecture. One issue is the timing of generating the subkeys. The control unit would play a large part of determining how long subkeys are held and when they would be replaced. Control unit area managing the subkey registers could be a large contributor.