DES, 3DES and AES – Part 2/2

Advanced Encryption Standard (AES) is a Block Cipher that require the following:

  1. AES shall be publicly defined.
  2. AES shall be a symmetric block cipher.
  3. AES shall be implementable in both hardware and software.
  4. AES shall be designed so that the key length may be increased as needed.
  5. AES block size n = 128 bits, key size k = 128, 192, 256 bits.


Encode input as 16-byte string by performing the following steps 10 times:

  1. (SubBytes) A fixed substitution step (The Rijndael S-Box).
  2. (ShiftRows) A fixed transposition step.
  3. (MixColumns) Consider input as four 4-byte sequences. Fixed substitution based on a linear transformation.
  4. (AddRoundKey) XOR with the key (bit operation).


Note: Each round uses a different round-key (that is derived in a standard way from the key).


The following link explains how AES Rijndael works?


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