What is Advanced Encryption Standard (AES)? Features and Applications

The Advanced Encryption Standard (AES) is a pivotal encryption algorithm that has become the backbone of data security in the digital age.

Established by the U.S. National Institute of Standards and Technology (NIST) in 2001, AES replaced the Data Encryption Standard (DES) as the go-to method for encrypting electronic data.

Its robust security features and efficiency have made it a cornerstone of modern cryptography, protecting sensitive information from cyber threats across various applications.

Understanding Advanced Encryption Standard (AES)

AES is a symmetric block cipher, meaning it uses the same key for both encryption and decryption processes.

It operates on fixed-size blocks of data, specifically 128 bits, and supports key lengths of 128, 192, or 256 bits.

This flexibility in key size allows AES to offer varying levels of security, making it adaptable to different needs and threats.

The algorithm's design is based on a substitution-permutation network, which involves a series of linked operations that substitute and shuffle the input data.

This structure provides strong resistance against cryptanalysis, ensuring that even if part of the data is compromised, the overall security remains intact.

Key Features of AES

• Block Cipher: AES encrypts data in blocks of 128 bits each. This means it takes a 128-bit block as input and outputs a 128-bit block of encrypted ciphertext.
• Key Sizes: AES supports three key sizes—128, 192, and 256 bits—allowing users to choose the level of security that best suits their needs.
• Rounds: The number of rounds in AES depends on the key length: 10 rounds for a 128-bit key, 12 rounds for a 192-bit key, and 14 rounds for a 256-bit key.
• Substitution-Permutation Network: AES relies on this principle to provide security through substitution (replacing data with other data) and permutation (rearranging data).

Working of The Cipher

AES operates on bytes rather than bits, processing 128 bits (or 16 bytes) of input data at a time. The encryption process involves multiple rounds, each consisting of specific steps designed to obfuscate the data thoroughly.

Creation of Round Keys

Before encryption begins, AES generates round keys from the initial key using a process known as the Key Schedule algorithm. These round keys are used in each round of encryption to ensure that each stage produces unique results.

Encryption Process

AES treats each block as a 16-byte grid arranged in a column-major format:

[ b0 | b4 | b8 | b12 ]

[ b1 | b5 | b9 | b13 ]

[ b2 | b6 | b10| b14 ]

[ b3 | b7 | b11| b15 ]

Each round consists of four primary steps:

1. SubBytes: This step implements substitution using an S-box lookup table. Each byte is replaced by another byte according to predefined rules, ensuring no byte is substituted by itself or its complement.
2. ShiftRows: The rows in the grid are shifted left by varying numbers:
• The first row remains unchanged.
• The second row shifts one position to the left.
• The third row shifts two positions to the left.
• The fourth row shifts three positions to the left.
3. MixColumns: Each column undergoes matrix multiplication with a fixed matrix. This step changes the positions of bytes within each column but is omitted in the final round for efficiency.
4. Add Round Key: The output from MixColumns is XORed with the corresponding round key generated earlier.

After completing all rounds, AES outputs a 128-bit block of encrypted data. This process repeats until all input data is encrypted.

How AES Encryption Works

AES operates on fixed-size blocks of data, specifically 128 bits, and supports three different key lengths: 128, 192, and 256 bits. These key lengths correspond to the three AES variants:

1. AES-128: Uses a 128-bit key length and performs 10 rounds of encryption.
2. AES-192: Uses a 192-bit key length and performs 12 rounds of encryption.
3. AES-256: Uses a 256-bit key length and performs 14 rounds of encryption.

Each round of encryption involves several processing steps, including substitution, transposition, and mixing of the plaintext input to transform it into ciphertext.

The number of rounds increases with the key length, enhancing security by making the encryption harder to crack.

Decryption Process

Decryption in AES is essentially the reverse of encryption. It involves applying inverse operations to retrieve the original plaintext from ciphertext:

1. Add Round Key: XORs the ciphertext with the round key.
2. Inverse MixColumns: Similar to MixColumns but uses a different matrix for multiplication.
3. ShiftRows: Reverses the row shifts applied during encryption.
4. Inverse SubBytes: Uses an inverse S-box for substitution.

Each block undergoes these reverse operations through its respective number of rounds based on key size (10, 12, or 14).

Applications of AES

AES's versatility and strength make it suitable for various applications requiring secure data storage and transmission:

1. Wireless Security: AES secures wireless networks like Wi-Fi by ensuring data confidentiality and preventing unauthorized access.
2. Database Encryption: Sensitive data stored in databases can be encrypted using AES to protect against breaches and unauthorized access.
3. Secure Communications: Protocols for internet communications, email, instant messaging, and voice/video calls leverage AES to maintain confidentiality.
4. Data Storage: Encrypting sensitive data on hard drives, USB drives, and other storage media with AES protects against unauthorized access if devices are lost or stolen.
5. Virtual Private Networks (VPNs): VPN protocols use AES to secure communication between user devices and remote servers, keeping transmitted data private from eavesdroppers.
6. Secure Storage of Passwords: Instead of storing plaintext passwords, systems use AES to encrypt passwords before storage, adding an extra layer of protection.
7. File and Disk Encryption: AES encrypts files and folders on computers and external storage devices, safeguarding sensitive information during storage or transfer.

The Advanced Encryption Standard (AES) has proven itself as an indomitable force in cryptography since its introduction over two decades ago.

Despite advances in technology and cryptanalysis techniques, AES remains unbroken due to its robust design and efficient implementation.

Modern CPUs often integrate AES instruction sets to enhance speed and security for applications using this encryption method.

While vulnerabilities may exist in specific implementations or usage scenarios, these do not compromise the fundamental strength of AES itself.