What Protects Your Privacy Like No Other Method? … AES

In this article we will look at the basic stages of AES encryption.

Data blocks

With AES we have blocks of 16 bytes (128 bits) and with key sizes of 16, 24, 32 bytes. We go through a number of processes and where we operate on 16 bytes as an input and output. Each block, known as a state, is operated on as a 4x4 matrix, such as:

01 02 03 04
05 06 06 07
08 09 0A 0B
0C 0D 0E 0F

For different key sizes we go through a number of rounds (N):

• 128-bit (16 bytes) key -> N=10 rounds
• 192-bit (24 bytes) key -> N=12 rounds
• 256-bit (32 bytes) key -> N=14 rounds

Figure 1 outlines the process for 128-bit encryption, and where we have 10 rounds. For a 128-bit key it is expanded to 44 words with 33 bits each, and where each round uses four words (128 bits) as an input for each round. With Round 0, the initial transformation consists of add round key. The following rounds (apart from the final round) consists of:

• Substitute Bytes.
• Shift Row.
• Mix Column.
• Add round key.