6. The Internal Functions of Rijndael in Advanced Encryption Standard Implementation
Rijndael is a block cipher. The messages are broken into blocks of a predetermined length and each block is encrypted independently of the others. Rijndael operates on blocks that are 128 bits in length. There are actually three variants of the Rijndael cipher, each of which uses a different key length. Permissible key lengths are 128, 192, and 256 bits. The details of Rijndael may be found in Bennett and Gilles (1984), but we give an overview here [2,3].
Mathematical Preliminaries
Within a block, the fundamental unit operated on is a byte: that is, 8 bits. Bytes can be interpreted in two different ways. A byte is given in terms of its bits as b7b6b5b4b3b2b1b0
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