AES, the Advanced Encryption Standard, is a modern symmetric-key block cipher encryption method that has succeeded the renowned Data Encryption Standard (DES). IBM developed DES in the 1970s, and the US government approved it as a standard in 1977. Various applications have widely utilized DES for data encryption and decryption, including secure communication and financial transactions.

## General Working

• AES operates on 128-bit data blocks using symmetric-key encryption.
• It applies mathematical operations during each round, thereby effectively transforming plaintext into ciphertext.
• For encryption, It employs substitution, permutation, and XOR operations.
• Key scheduling generates round subkeys from the original encryption key.
• It expands the data block, mixes it with the subkey, performs substitution using S-boxes, and permutes it.
• The encryption process repeats for multiple rounds, guaranteeing comprehensive data encryption. Furthermore, a final permutation is applied to successfully generate the ciphertext.
• During decryption, It reverses the process by employing the round subkeys in a reverse manner.
• It provides robust cryptographic security through these operations and key-dependent S-boxes.

## Example

Let’s delve into the inner workings of AES (Advanced Encryption Standard) with a simple example to gain a better understanding:

Suppose we have a 128-bit plaintext message: “HelloAES12345678.” Our objective is to encrypt this message using AES.

### Step 1: Key Expansion

AES expands the original encryption key, typically 128, 192, or 256 bits long. Through a series of transformations, this process generates a set of round subkeys utilized in each encryption round.

### Step 2: Initial Round

In the initial round, It takes the 128-bit plaintext message and performs an XOR operation with the first round subkey.

### Step 3: Rounds of Substitution, Permutation, and XOR

AES consists of multiple rounds, each involving three main operations: substitution, permutation, and XOR.

Substitution: It employs S-boxes, substituting each byte of the plaintext with a corresponding value from the S-box. This non-linear substitution enhances security.

Permutation: It rearranges the bytes of the data block based on a fixed permutation table, introducing additional complexity.

XOR: In each round, the permutation result undergoes XOR with the round subkey, introducing a key-dependent aspect into the encryption.

These operations repeat for a specified number of rounds (10, 12, or 14 rounds based on the key length: 128, 192, or 256 bits, respectively).

### Step 4: Final Round

In the final round, the algorithm excludes the permutation step and solely performs substitution and XOR operations.

### Step 5: Ciphertext Generation

After completing the encryption rounds, It generates the 128-bit ciphertext, representing the encrypted form of the original plaintext message.

In our example, It would produce the encrypted ciphertext using the provided plaintext and specified key. Each step ensures the encrypted data remains secure and resistant to deciphering without the corresponding key.

By following this process, Advanced Encryption Standard offers robust encryption, safeguarding sensitive data in applications such as secure communication, financial transactions, and data storage.

• Strong Security: AES offers robust cryptographic security, resisting known attacks.
• Versatility: It can be implemented on various platforms and operating systems.
• Efficient Performance: AES is computationally efficient, suitable for real-time applications.
• Widely Accepted: AES is a standardized and widely accepted encryption standard.