AES

The **Advanced Encryption Standard** (**AES**), also known by its original name **Rijndael** (Dutch pronunciation: [ˈrɛindaːl]), 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 a subset of the Rijndael cipher developed by two Belgian cryptographers, Vincent Rijmen and Joan Daemen, who submitted a proposal to NIST during the AES selection process. Rijndael is a family of ciphers with different key and block sizes.

AES became effective as a federal government standard on May 26, 2002, after approval by the Secretary of Commerce. AES is included in the ISO/IEC 18033-3 standard. AES is available in
many different encryption packages, and is the first (and only) publicly accessible cipher approved by the National Security Agency (NSA) for top secret information when used in an NSA approved cryptographic module (see Security of AES, below).

### **Description of the cipher**

AES is based on a design principle known as a substitution-permutation network, a combination of both substitution and permutation, and is fast in both software and hardware. Unlike its predecessor DES, AES does not use a Feistel network. AES is a variant of Rijndael which has a fixed block size of 128 bits, and a key size of 128, 192, or 256 bits. By contrast, the Rijndael specification *per se* is specified with block and key sizes that may be any multiple of 32 bits, both with a minimum of 128 and a maximum of 256 bits.

AES operates on a 4 × 4 column-major order matrix of bytes, termed the *state*, although some versions of Rijndael have a larger block size and have additional columns in the state. Most AES calculations are done in a
particular finite field.For instance, if there are 16 bytes, , these bytes are represented as this matrix:

The key size used for an AES cipher specifies the number of
repetitions of transformation rounds that convert the input, called the plaintext, into the final output, called the ciphertext. The number of cycles of repetition are as follows:

* 10 cycles of repetition for 128-bit keys.
* 12 cycles of repetition for 192-bit keys.
* 14 cycles of repetition for 256-bit keys.

Each round consists of several processing steps, each containing four similar but different stages, including one that depends on the encryption key itself. A set of reverse rounds are applied to transform ciphertext back into the original plaintext using the same encryption key.

1. ↑ "Rijndael". Retrieved March 9, 2015."Rijndael". Retrieved March 9, 2015.
2. ↑ 2.0 2.1 Daemen, Joan; Rijmen, Vincent (March 9, 2003). "AES Proposal: Rijndael" (PDF). National Institute of Standards and Technology. p. 1. Retrieved 21 February 2013.
3. ↑ "Announcing the ADVANCED ENCRYPTION STANDARD (AES)" (PDF). Federal Information Processing Standards Publication 197. United States National Institute of Standards and Technology (NIST). November 26, 2001. Retrieved October 2, 2012.
4. ↑ John Schwartz (October 3, 2000). "U.S. Selects a New Encryption Technique". New York Times.
5. ↑ Bruce Schneier; John Kelsey; Doug Whiting; David Wagner; Chris Hall; Niels Ferguson; Tadayoshi Kohno; et al. (May 2000). "The Twofish Team's Final Comments on AES Selection" (PDF).

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