The Rainy Doll Who Advanced The Cause of Privacy More Than Anything Else in History

NIST held a competition around the turn of the millennium for a new standard: AES (Advanced Encryption Standard) [read about competition here]. After a short of five candidates, the RIJNDAEL (‘Rain-doll’) method came out on top. It uses a 128-bit block size, and supported 128-bit, 192-bit and 256-bit encryption keys. It has since become the standard method for encrypting data, so let’s have a look at how it works:

Data blocks

With AES we have blocks of 16 bytes (128 bits) and with key sizes of 16, 24, 32 bytes. We go through a number of processes and where we operate on 16 bytes as an input and output. Each block, known as a state, is operated on as a 4x4 matrix, such as:

01 02 03 04
05 06 06 07
08 09 0A 0B
0C 0D 0E 0F

For different key sizes we go through a number of rounds (N):

• 128-bit (16 bytes) key -> N=10 rounds
• 192-bit (24 bytes) key -> N=12 rounds
• 256-bit (32 bytes) key ->…