What is AES? Advanced Encryption Standard and its modes of operation

AES is a symmetric encryption algorithm

In today’s digital age, data security is a critical priority for every organization. As cyber threats continue to rise, AES (Advanced Encryption Standard) has emerged as one of the leading symmetric encryption algorithms trusted worldwide. So, what is AES, how does it work, and why does it play such a vital role in protecting sensitive information? Let’s explore the answers in this article from TopOnTech.

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What Is AES?

AES (Advanced Encryption Standard) is a symmetric block cipher algorithm officially published by the National Institute of Standards and Technology (NIST) in 2001.

Developed to replace the outdated Data Encryption Standard (DES), AES has become the most widely used encryption standard in the world today. It is based on a substitution-permutation network design, enabling the encryption of 128-bit data blocks using keys of 128, 192, or 256 bits in length.

what is AES
AES is a symmetric encryption algorithm based on the substitution-permutation network design (Source: Internet).

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Applications of the AES Symmetric Encryption Algorithm

Thanks to its strong security and optimal performance, AES encryption is widely used across various industries:

  • Personal devices: AES is used to protect sensitive information on personal computers, smartphones, and storage devices. Protocols such as SSL/TLS (for secure web browsing), VPNs (virtual private networks), and WPA2/WPA3 (Wi-Fi security) all rely on AES to encrypt transmitted data.
  • Financial sector: Online banking transactions, electronic payments, and other financial systems depend on AES symmetric encryption to ensure data integrity and confidentiality, minimizing the risk of duplication or unauthorized access to financial software.
  • Cloud storage: Major cloud storage providers like Google Drive, Dropbox, and OneDrive use AES encryption to secure user data, enhancing protection during both storage and transmission.
  • Government and defense: Due to its exceptional security capabilities, AES is deployed in high-level security systems within government agencies and military organizations.

These applications highlight the essential role of the Advanced Encryption Standard in modern data protection. Understanding what AES is helps individuals and organizations choose the right encryption solutions to meet information security requirements across different sectors.

Uses of AES encryption in personal devices
AES is used to protect information on personal devices (Source: Internet).

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How Does AES Work?

To fully understand what AES is, it’s important to grasp how the algorithm functions. AES encryption operates through two main processes: encryption, which transforms plaintext into ciphertext, and decryption, which recovers plaintext from the encrypted data. Both processes use the same shared secret key.

Key Expansion

AES requires the generation of a set of round keys derived from the original key, used in both encryption and decryption. The number of rounds and round keys depends on the key length:

  • 128-bit key: 10 rounds
  • 192-bit key: 12 rounds
  • 256-bit key: 14 rounds

Each round uses a unique subkey generated through a complex key expansion algorithm from the original encryption key.

In each encryption round (except the final round), the data block undergoes four main transformations:

Step 1: SubBytes

This nonlinear substitution step replaces each byte in the data block using a fixed lookup table called the S-box. The goal of SubBytes is to introduce confusion, making the relationship between the plaintext and ciphertext more complex, and helping defend against statistical attacks.

Step 2: ShiftRows

This step performs a circular left shift on each row of the state matrix. The first row remains unchanged, the second row shifts 1 byte to the left, the third row shifts 2 bytes, and the fourth row shifts 3 bytes. ShiftRows increases diffusion by spreading bytes across columns.

Step 3: MixColumns

MixColumns applies a linear transformation to each column of the state matrix. Each column is multiplied by a fixed matrix in the Galois Field GF(2^8), ensuring that every output byte is affected by all input bytes in that column. This enhances diffusion. The final round omits the MixColumns step.

Step 4: AddRoundKey

In the final step of each round, a bitwise XOR operation is performed between the current state and the round subkey. This is where the encryption key directly influences the transformation, adding non-linearity and security to the process.

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Decryption

The AES decryption process essentially reverses the steps of encryption, applying inverse transformations and using the round keys in reverse order. Understanding this mechanism further clarifies what AES is and why it is highly regarded for its integrity and efficiency. The decryption process includes the following steps:

Step 1: AddRoundKey

Similar to the encryption step, this operation performs a bitwise XOR with the corresponding round key. However, in decryption, the round keys are applied in the reverse order compared to the encryption process.

Step 2: Inverse MixColumns

This is the inverse of the MixColumns transformation, using an inverse matrix to restore the original columns. The first round of decryption (which corresponds to the last encryption round) skips this step.

Step 3: Inverse ShiftRows

This reverses the ShiftRows operation by shifting the rows in the opposite direction, using the same number of bytes as in the original step.

Step 4: Inverse SubBytes

This step is the inverse of SubBytes, applying the inverse S-box lookup to restore each byte to its original value.

How AES encryption and decryption work
AES operates through both encryption and decryption processes (Source: Internet)

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Advantages and Limitations of the AES Algorithm

After understanding what AES is and its critical role in data protection, organizations should carefully consider both its strengths and limitations before implementation.

Advantages

  • High security: AES encryption is designed to resist common cryptographic attacks such as brute-force attacks, statistical attacks, and differential analysis. To date, there have been no successful full-scale attacks that break AES completely.
  • Strong performance: AES is optimized to perform efficiently across a wide range of hardware and software platforms, from compact embedded devices to high-performance servers.
  • Flexibility: AES supports multiple key lengths (128, 192, and 256 bits), allowing users to choose the level of security that best fits their specific needs.
  • International standard: Recognized by NIST as a U.S. federal encryption standard, AES has become the global go-to solution for secure applications and systems.
Advantages and disadvantages of AES encryption
The AES algorithm offers several advantages in information security (Source: Internet)

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Limitations

  • Complexity: Compared to some simpler encryption algorithms, AES has a more intricate structure that requires advanced technical knowledge to implement and fully understand its internal workings.
  • Key management: Like all symmetric encryption algorithms, AES requires secure key management and distribution. If the encryption key is exposed, the security of the entire system is compromised.
  • Implementation vulnerabilities: Although the AES algorithm itself is robust, vulnerabilities may arise from improper implementation or insecure integration into systems, leading to potential security risks.
  • Cost: Implementing AES at scale may involve significant investment in both hardware and software to ensure maximum data protection. The larger and more complex the data protection infrastructure, the higher the cost of deployment and maintenance.

AES is one of the most powerful and reliable encryption algorithms available today, playing a vital role in protecting data in the digital era. This article has explained what AES is, how it works, and why it is essential to modern cybersecurity. By understanding the foundations of AES encryption, users and organizations can confidently interact in today’s digital environment with improved data protection.

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