3.2.1 Encryption and Decryption

The AES is capable of using cryptographic keys of 128/192/256 bits to encrypt and decrypt data in blocks of 128 bits. In Cipher Feedback Mode (CFB), five data sizes are possible (8, 16, 32, 64, or 128 bits).

The input to the encryption processes of the CBC, CFB, and OFB modes includes, in addition to the plaintext, a 128-bit data block called the Initialization Vector (IV). The Initialization Vector is used in the initial step in the encryption of a message and in the corresponding decryption of the message.

There are three encryption/decryption start modes:

  • Manual Mode: Start encryption/decryption manually

  • Auto Start Mode: Once the correct number of input data registers is written, processing is automatically started, DMA operation uses this mode

  • Last Output Data Mode (LOD): This mode is used to generate message authentication code (MAC) on data in CCM mode of operation