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Advanced Encryption Standard

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In cryptography, the Advanced Encryption Standard (AES), which is also known as Rijndael, is a block cipher algorithm used as an encryption standard by the U.S. government. It has been looked at a lot and is now used all over the world, as was the case with its predecessor, the Data Encryption Standard (DES).[1] AES was announced by National Institute of Standards and Technology (NIST) as U.S. FIPS PUB 197 (FIPS 197) on November 26, 2001 after a 5-year standardization process in which fifteen competing designs were presented and evaluated before Rijndael was selected as the most suitable. It became effective as a standard May 26, 2002. As of 2008, AES is one of the most popular algorithms used in symmetric key cryptography. It is available by choice in many different encryption packages. This marks the first time that the public has had access to a cipher algorithm approved by NSA for top secret information.

This cipher algorithm was developed by two Belgian cryptographers, Joan Daemen and Vincent Rijmen, and submitted to the AES selection process under the name "Rijndael", a portmanteau of the names of the inventors. (Rijndael is pronounced [rɛindaːl]).[2]

Strictly speaking, AES is not precisely Rijndael (although in practice they are used interchangeably), following are the main differences:

  • Rijndael supports a larger range of block sizes and key sizes and can use any combination of key and block sizes in any multiple of 32 bits, with a minimum of 128 bits and a maximum of 256 bits.
  • AES has a fixed block sizes of 128 bits and three values of key size 128, 192, or 256 bits.
"The design and strength of all key lengths of the AES algorithm (i.e., 128, 192 and 256) are sufficient to protect classified information up to the SECRET level. TOP SECRET information will require use of either the 192 or 256 key lengths. The implementation of AES in products intended to protect national security systems and/or information must be reviewed and certified by NSA prior to their acquisition and use."[3]

Many AES public products use 128-bit secret keys by default; it is possible that the NSA may assume that 128-bit secret keys are weak and they may prefer longer keys for top secret documents.

Unlike DES (the predecessor of AES), AES is a substitution-permutation network, not a Feistel network. AES is fast in both software and hardware, is relatively easy to implement, and requires little memory. As a new encryption standard, it is currently being deployed on a large scale on various platforms.

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