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Advanced Encryption Standard

Vincent Rijmen

The Advanced Encryption Standard is the result of a 3 year long public request for proposals that was started in 1997 by the NIST (National Institute Of Standards and Technology) a unit of the U.S. Commerce Department.

In 1999 five finalists where chosen from over 15 submissions, namely Rijndael, Mars, RC6, Serpent and Twofish.

All algorithms had to fullfill several preconditions:

It should be possible to choose between key sizes and block sizes of 128, 192 or 256 bits.
But in the course of the standardization process the blocksize was later set to a fixed length of 128 bits which makes the design of a block cipher a lot easier and doesn't affect the security of the algorithms.
Additionally to high requirements according security, matters of speed were also important when it came to make a decision.

V.Rijmen(left) and J.Daemen(right)

At the end of the standardization process, Rijndael, a cipher developed by the two Belgian cryptoanalysts Joan Daemen and Vincent Rijmen was announced the winner and became the successor of the Data Encryption Standard.

Rijndael uses a variable number of rounds, depending on key/block sizes, as follows:

       9 rounds if the key/block size is 128 bits

      11 rounds if the key/block size is 192 bits

      13 rounds if the key/block size is 256 bits

Rijndael is a substitution linear transformation cipher, not requiring a Feistel network. It uses triple discrete invertible uniform transformations (layers).
Specifically, these are: Linear Mix Transform, Non-linear Transform and Key Addition Transform.

The technical description of the new standard was published by the NIST as FIPS PUB 197 in the year 2001.



AES-Lounge at Graz University of Technology

(find out about recent attacks on AES and different AES implementations)


A good description of the Rijndael scheme


Find out how AES works by using this applet


Biography of Vincent Rijmen


Biography of Joan Daemen