How the Advanced Encryption Standard (AES ) algorithm work

Advanced Encryption Standard (AES)

•   The AES algorithm is a symmetrical block cipher that turns plain text into ciphertext in blocks of 128 bits utilizing keys of 128, 192, and 256 bits. The AES algorithm is a worldwide standard because it is considered secure.

• To produce ciphertext, the AES algorithm utilizes a substitution-permutation (SP) network with many rounds. The number of rounds is determined on the key size. Ten rounds are dictated by a 128-bit key size, 12 rounds by a 192-bit key size, and 14 rounds by a 256-bit key size.Each of these rounds requires a round key, because of the algorithm only accepts one key, it must be enlarged to obtain keys for each round, including round 0. 

Each round in the algorithm consists of four steps:

1. Substitution of the bytes

The bytes of the block text are first substituted according to rulesimposed by predefined S-boxes  (short for substitution boxes).

2. Shifting the rows

The permutation stage follows next. All rows except the first are shifted by one in this stage.

3. Mixing the columns

The Hill cipher is used in the third phase to further muddle up the message by mixing the block's columns.

4. Adding the round key

The message is then XORed with the appropriate round key in the last step.

These stages, when followed consistently, ensure that the final ciphertext is secure.