Advanced Encryption Standard

The Advanced Encryption Standard (AES) is a specification for the encryption of electronic data established by the U.S. National Institute of Standards and Technology (NIST) in 2001. AES is based on the Rijndael cipher developed by two Belgian cryptographers, Joan Daemen and Vincent Rijmen, who submitted a proposal to NIST during the AES selection process.

History

AES was announced by NIST as U.S. FIPS PUB 197 (FIPS 197) on November 26, 2001, after a five-year standardization process in which fifteen competing designs were presented and evaluated before Rijndael was selected as the most suitable.

Design

AES is a symmetric key algorithm, meaning the same key is used for both encrypting and decrypting the data. It is a block cipher with a block size of 128 bits, and it supports key sizes of 128, 192, and 256 bits. The number of rounds in the encryption process depends on the key size: 10 rounds for 128-bit keys, 12 rounds for 192-bit keys, and 14 rounds for 256-bit keys.

Structure

AES operates on a 4x4 column-major order matrix of bytes, known as the state. The algorithm consists of a series of linked operations, including:

• SubBytes: A non-linear substitution step where each byte is replaced with another according to a lookup table.
  

  SubBytes step in AES
• ShiftRows: A transposition step where each row of the state is shifted cyclically a certain number of steps.
  

  ShiftRows step in AES
• 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 byte of the round key using bitwise XOR.

The initial round key addition is followed by nine, eleven, or thirteen rounds of the four steps above, depending on the key size, with a final round that omits the MixColumns step.

Security

AES is considered secure and is widely used across the globe. It is the first and only publicly accessible cipher approved by the U.S. National Security Agency (NSA) for top secret information when used in an NSA-approved cryptographic module.

Applications

AES is used worldwide to secure data in various applications, including:

• Wi-Fi security (WPA2)
• SSL/TLS protocols for secure web browsing
• Disk encryption systems
• Virtual private networks (VPNs)

Also see

• Data Encryption Standard
• Block cipher modes of operation
• Cryptography
• Public-key cryptography