Advanced Encryption Standard (AES), also known as Rijndael, is a block cipher adopted as an encryption standard by the U.S. government. AES is a symmetric-key algorithm that was designed to replace its outdated predecessor DES (Data Encryption Standard).

This algorithm appeared as a result of the public competition announced by the National Institute of Standards and Technology (NIST) in 1997 and finished in 2000. Five different algorithms got into the second tour of the competition and Rijndael was announced the winner. The algorithm was chosen due to such features as security, performance rate, effectiveness, easy implementation on various software and hardware platforms and, of course, flexibility.

Rijndael remained fast on a wide range of software and hardware in all available modes. Rijndael has a perfect key initialization time and requires minimum memory. As of 2006, Rijndael is one of the most popular symmetric-key encryption algorithms. This algorithm was developed by two Belgian cryptography specialists. Vincent Rijmen and Joan Daemen submitted it to the AES selection process under the name “Rijndael”.

Strictly speaking, AES is not identical to Rijndael because Rijndael supports a larger range of block and key sizes. AES has a fixed block size of 128 bits and the key size may be 128, 192 or 256 bits, whereas Rijndael supports keys and blocks of various sizes divisible by 32 bits – from 128 bits to 256 bits. Also it is possible to expand the encryption key. It turns out that AES is a limited implementation of the Rijndael algorithm. Unlike public key encryption algorithms where pairs of keys are used for encryption/decryption, symmetric-key algorithms, including Rijndael, use one key for these operations.

As it was mentioned above, AES is a descendant of the older Data Encryption Standard (DES). DES remained a standard from 1977 to 1998 when the level of software and hardware development, as well as the development of the cryptanalysis, allowed a DES data block to be decrypted within 56 hours.

Complete AES-related information is available on the AES home page http://csrc.nist.gov/archive/aes/index.html.