The AES supports the following modes of operation:
The data preprocessing, data postprocessing and data chaining for the concerned modes are performed automatically. Refer to the NIST Special Publication 800-38A and NIST Special Publication 800-38D for more complete information.
Mode selection is done by configuring the OPMOD field in AES_MR.
In CFB mode, five data sizes are possible (8, 16, 32, 64 or 128 bits), configurable by means of AES_MR.CFBS.
In CTR mode, the size of the block counter embedded in the module is 16 bits. Therefore, there is a rollover after processing 1 Mbyte of data. If the file to be processed is greater than 1 Mbyte, this file must be split into fragments of 1 Mbyte or less for the first fragment if the initial value of the counter is greater than 0. Prior to loading the first fragment into AES_IDATARx, AES_IVRx must be fully programmed with the initial counter value. For any fragment, after the transfer is completed and prior to transferring the next fragment, AES_IVRx must be programmed with the appropriate counter value.