In 1997, the National Institute of Standards and Technology (NIST) adopted the Advanced Encryption Standard (AES) as a replacement for DES and 3DES. The standards is based on the Rijndael algorithm created by Drs. Joan Daemon and Vincent Rijmen of Belgium. NIST chose AES after considering several possible candidates.
The Rijndael algorithm uses block sizes of 12 8, 192, and 256 bits with keys of the same lengths. The number of operating rounds used is related to the size of the key: 10, 12, and 14 respectively. AES supports only one block size.
To encrypt a plaintext message, the input is placed into a 128-bit state array while the key is placed into a similar table. Then, four major operations are conducted on the message:
- Substitute bytes – an S-box is used to substitute byte-by-byte on the entire block
- Shift rows – each row in the table is offsetted
- Mix columns – each value in a column is substituted based on the values of the data
- Add round key – each byte is XORed with the key for the current round. Additional rounds are performed with a different key.
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