Advanced Encryption Standard

= Advanced Encryption Standard (AES) =

The Advanced Encryption Standard (AES) is a symmetric encryption algorithm widely used across the globe to secure data. It was established as a standard by the U.S. National Institute of Standards and Technology (NIST) in 2001, following a rigorous selection process.

History

AES was developed to replace the Data Encryption Standard (DES), which had become vulnerable to brute-force attacks due to its relatively short key length. In 1997, NIST initiated a public competition to select a new encryption standard. The winning algorithm, Rijndael, was designed by Belgian cryptographers Vincent Rijmen and Joan Daemen. It was selected in 2000 and officially became the AES standard in 2001.

Algorithm Structure

AES is a block cipher, meaning it encrypts data in fixed-size blocks. The standard block size is 128 bits, and it supports key sizes of 128, 192, and 256 bits. The algorithm consists of a series of transformations that are applied to the data block in multiple rounds.

Key Features

• Symmetric Key Algorithm: AES uses the same key for both encryption and decryption.
• Block Size: Fixed at 128 bits.
• Key Sizes: 128, 192, or 256 bits.
• Number of Rounds: 10 rounds for 128-bit keys, 12 rounds for 192-bit keys, and 14 rounds for 256-bit keys.

AES Encryption Process

The AES encryption process involves several steps:

1. Key Expansion

The original key is expanded into a series of round keys using a key schedule. This process involves the use of the Rijndael key schedule algorithm.

2. Initial Round

• AddRoundKey: Each byte of the state is combined with a block of the round key using bitwise XOR.

3. Main Rounds

Each main round consists of four transformations:

• SubBytes: A non-linear substitution step where each byte is replaced with another according to a lookup table (S-box).
• ShiftRows: A transposition step where each row of the state is shifted cyclically a certain number of steps.
• MixColumns: A mixing operation which operates on the columns of the state, combining the four bytes in each column.
• AddRoundKey: Each byte of the state is combined with a block of the round key using bitwise XOR.

4. Final Round

The final round is similar to the main rounds but omits the MixColumns step.

AES Decryption Process

The decryption process of AES is the reverse of the encryption process, using the inverse transformations:

• InvSubBytes: The inverse of the SubBytes step.
• InvShiftRows: The inverse of the ShiftRows step.
• InvMixColumns: The inverse of the MixColumns step.
• AddRoundKey: The same as in encryption.

Security

AES is considered highly secure and is used worldwide to protect sensitive data. Its security is based on the difficulty of performing a brute-force attack due to the large key sizes. As of 2023, no practical attacks have been found that can break AES when implemented correctly.

Applications

AES is used in a variety of applications, including:

• Secure Communications: Used in protocols like TLS/SSL for secure internet communications.
• Data Encryption: Used to encrypt files, databases, and other data storage.
• Wireless Security: Used in WPA2 for securing wireless networks.

Conclusion

The Advanced Encryption Standard is a cornerstone of modern cryptography, providing robust security for digital communications and data storage. Its adoption as a global standard underscores its importance and effectiveness in protecting information in the digital age.

References

• National Institute of Standards and Technology (NIST). "FIPS PUB 197: Advanced Encryption Standard (AES)." 2001.
• Daemen, Joan, and Vincent Rijmen. "The Design of Rijndael: AES - The Advanced Encryption Standard." Springer, 2002.