Advanced Encryption Standard (AES)
In 2001, after an open competition, an encryption algorithm named Rijndael invented by cryptographers Joan Daemen and Vincent Rijmen was standardized as AES with minor modifications by NIST. So far, no attack has been found against AES that is more effective than the brute-force method. The original version of Rijndael permits different key and block sizes of 128 bits, 192 bits, and 256 bits. In the AES standard, however, only a 128-bit block size is allowed. However, key sizes of 128 bits, 192 bits, and 256 bits are permissible.
How AES works
During AES algorithm processing, a 4 × 4 array of bytes known as the state is modified using multiple rounds. Full encryption requires 10 to 14 rounds, depending on the size of the key. The following table shows the key sizes and the required number of rounds:
| Key size | Number of rounds required |
| 128-bit | 10 rounds |
| 192-bit | 12 rounds |
| 256-bit | 14 rounds |
Once the state is initialized with the input to...