## National Institute of Science and Technology release Advanced Encryption Standard (AES)National Institute of Science and Technology release

May 16, 2023 |

The National Institute of Science and Technology has produced the updated Advanced Encryption Standard (AES) on 9 May 2023.

At 46 pages it is the usuallong and detailed publication one expects from NIST. That said, NIST are excellent publications.

Some relevant matters worth noting:

- A bit is a binary digit —0 or 1.
- a block is a sequence of 128 bits;
- the data input and output for the AES block ciphers are blocks.
- the key is a bit sequence that is typically established beforehand and maintained across many invocations of the block cipher.
- the basic processing unit is the byte — a sequence of eight bits.
- a byte value is denoted by the concatenation of the eight bits between braces
- when the bits of a byte are denoted by an indexed variable, the convention in this Standard is for the indices to decrease from left to right
- it is also convenient to denote byte values using hexadecimal notation. The 16 hexadecimal characters represent sequences of four bits
- internally, the algorithms for the AES block ciphers are performed on a two-dimensional (fourby-four) array of bytes called the state.
- a word is a sequence of four bytes; a block consists of four words.
- in the algorithms for the AES block ciphers can be expressed in terms of matrix multiplication. In particular, a distinct fxed matrix is specifed for each transformation.
- the core of the algorithms for CIPHER() and INVCIPHER() is a sequence of fxed transformations of the state called a round. Each round requires an additional input called the round key; the round key is a block that is usually represented as a sequence of four words (i.e., 16 bytes)
- an expansion routine, denoted by KEYEXPANSION(), takes the block cipher key as input and generates the round keys as output.
- the input to KEYEXPANSION() is represented as an array of words, denoted by key, and the output is an expanded array of words, denoted by w, called the key schedule