Real 802.11 Security: Wi-Fi Protected Access and 802.11i

Appendix A. Overview of the AES Block Cipher

The AES block cipher is the same as the Rijndael algorithm but with a fixed block size of 128 bits (see Chapter 12). In IEEE 802.11i RSN, a further simplification is made by restricting the key size as well as the block size to 128 bits. The following description relates only to the RSN version.

You can think of the encryption of the block of data as a sort of production process in which various operations are applied repeatedly until the finished product, the ciphertext, is produced. A medieval blacksmith made a sword by starting with a strip of iron and repeatedly heating it, hammering it, adding impurities, folding it, and quenching it in cold water. By folding the metal ten times, the sword ended ...