Advanced Encryption Standard (AES)

April 30, 2023

Advanced Encryption Standard (AES) is a symmetric block cipher algorithm used to encrypt and decrypt digital data. It is widely used for secure data transmission over the internet, including sensitive information like banking transactions, passwords, and personal identification numbers (PINs). AES is considered to be one of the most secure encryption algorithms, and it is the standard encryption algorithm used by the United States government.

History and Development

AES was developed by two Belgian cryptographers, Joan Daemen and Vincent Rijmen, in 1997. It was designed to replace the aging Data Encryption Standard (DES), which had become vulnerable to brute-force attacks due to its short key length of 56 bits.

The National Institute of Standards and Technology (NIST) launched a competition in 1997 to select the next-generation encryption standard, which was won by the Rijndael cipher, a variation of AES. In 2001, AES became the standard encryption algorithm for the US government and was subsequently adopted by many other countries and organizations.

Purpose and Usage

The primary purpose of AES is to secure digital data transmission by encrypting plain text into cipher text. It is a symmetric-key algorithm, which means that the same key is used for both encryption and decryption. AES is used in various applications, including messaging applications, file storage, and secure network communication.

AES is also used in conjunction with other security protocols such as SSL/TLS to provide secure online transactions. It is used in VPNs to secure communications between two devices and in disk encryption to protect the data stored on hard drives or other storage devices.

Key Concepts and Principles

AES operates on fixed block sizes of 128 bits and encrypts data in blocks of 128, 192, or 256 bits. The key sizes for AES are 128, 192, or 256 bits, with the higher key sizes providing greater security.

AES uses a series of steps to encrypt data, including SubBytes, ShiftRows, MixColumns, and AddRoundKey. Each step involves mathematical operations on the data and the key to generate the cipher text.

SubBytes is a non-linear substitution step that replaces each byte of the block with a new byte based on a fixed table. The ShiftRows step shifts the rows of the block to create a diffusion effect. The MixColumns step uses matrix multiplication to transform the columns of the block. Finally, the AddRoundKey step adds the key to the block to generate the cipher text.

The reverse of these steps is used for decryption, starting with the AddRoundKey step and working backward through the steps to generate the original plain text.

Pseudocode and Implementation Details

The following pseudocode demonstrates the implementation of AES encryption:

function AES_encrypt(plaintext, key):
    key_schedule = key_expansion(key)
    state = plaintext
    state = add_round_key(state, key_schedule[0])
    for i in range(1, 10):
        state = sub_bytes(state)
        state = shift_rows(state)
        state = mix_columns(state)
        state = add_round_key(state, key_schedule[i])
    state = sub_bytes(state)
    state = shift_rows(state)
    state = add_round_key(state, key_schedule[10])
    ciphertext = state
    return ciphertext

The above pseudocode outlines the basic steps involved in the encryption process using AES. The implementation of AES varies depending on the programming language and framework used.

Examples and Use Cases

AES is used in various applications, including secure messaging apps like Signal, secure file sharing services like Dropbox, and disk encryption software like BitLocker. In addition, it is used to secure online transactions and communications, such as online banking transactions and secure web browsing.

For example, when a user logs into their online bank account, their login credentials are encrypted using AES to prevent unauthorized access. Similarly, when a user shops online or sends an email, the data is encrypted using AES to keep it secure.

Advantages and Disadvantages

The main advantage of AES is its security. It is considered to be one of the most secure encryption algorithms and is widely used for securing sensitive data. AES is also efficient and fast, making it suitable for use in various applications.

One of the disadvantages of AES is that it requires a high level of computer processing power to encrypt and decrypt large amounts of data. This can be an issue when encrypting data on low-powered devices or when encrypting large files.

Another potential disadvantage of AES is its susceptibility to side-channel attacks, where an attacker can obtain the encryption key by observing the physical characteristics of the device used for encryption. However, this is a theoretical vulnerability and is not considered a practical attack vector.

There are several variations of AES, including AES-CCM, AES-GCM, and AES-CBC. These variations provide additional security features, such as authenticated encryption and message integrity.

Another related algorithm is RSA, which is an asymmetric encryption algorithm used for secure key exchange. RSA is commonly used in conjunction with AES to provide end-to-end encryption for secure communications.

Overall, AES is an essential encryption algorithm that has become a cornerstone of secure data transmission over the internet. Its widespread adoption by governments and industries around the world is a testament to its effectiveness and reliability in securing sensitive data.