SWCU192 November 2021 CC1312R7 , CC1352P7 , CC2652P7 , CC2652R7
The composition of the AES core follows:
The AES key scheduler generates the round keys. During each round, a new subkey is generated from the input key to be XORed with the data. Round keys are generated on-the-fly and parallel to data processing to minimize register requirements. For encryption operations, the key sequencer transfers the initial key data to the AES core. For decryption operations, the key scheduler must provide the final subkey to the AES core so it can generate the subkeys in reverse order.
The AES core operates on the input block and performs the required substitution, shift, and mix operations. For each round, the encryption core receives the proper round key from the AES key scheduler. A fundamental component of the AES algorithm is the S-box. The S-box provides a unique
8-bit output for each 8-bit input.
The architecture of the AES decryption core is generally the same as the architecture of the encryption core. One difference is that the generation of round keys for decryption requires an initial conversion of the input key (always supplied by the host in the form of an encryption key) to the corresponding decryption key. This conversion is done by performing a dummy encryption operation and storing the final round key as a decryption key. The key scheduler is then reversed to generate the round keys for the decryption operation. Consequently, for each sequence of decryption operations under the same key, a single throughput reduction equal to the time to encrypt a single block occurs. When a decryption key is generated, subsequent decryption operations with the same key use this generated decryption key directly.