An Introduction to the Advanced Encryption Standard (AES)

What is AES?

The Advanced Encryption Standard (AES) is a cornerstone of modern data security. It is a symmetric-key encryption algorithm, meaning the same key is used for both encryption and decryption. AES operates on fixed-size blocks of data, typically 128 bits, and supports key sizes of 128, 192, and 256 bits. Its widespread adoption is due to its robustness, efficiency, and resistance to various cryptographic attacks.

Key Operations in AES

The AES encryption process involves a series of iterative rounds. Each round consists of four distinct transformation steps designed to confuse and diffuse the plaintext, making it unintelligible without the correct key. These steps are:

• SubBytes: A non-linear byte substitution using a pre-defined S-box.
• ShiftRows: A linear byte permutation that shifts rows of the state matrix.
• MixColumns: A linear transformation that mixes the bytes within each column.
• AddRoundKey: A key whitening step where the round key is XORed with the state.

The document provides a practical, step-by-step example to illustrate these operations, including key expansion and the data flow through multiple rounds.