Computer Security and Cryptography

9.14 AND THE WINNER IS!

Rijndael was announced as the winning algorithm in October 2000 [Daemen and Rijmen, 1999] and is specified in [FIPS, 2001, FIPS-197]. Susan Landau [2004] wrote

Daemen and Rijmen sought simiplicity – simplicity of specification and simplicity of analysis. Not every cryptographer sees simplicity as an important goal – two AES finalists, MARS and Twofish, have far more complex designs. Some observers felt that this complexity was part of the reason the two algorithms were not chosen as the Advanced Encryption Standard, as their round functions were simply too difficult to analyze fully.

Too difficult to analyze! Indeed!

Rijndael is a block cipher supporting a variety of plaintext block sizes and cipher key lengths. The cipher key k is an array of dimension 4 × Nk (a total of Nk 4-byte words)

Each {k_i,j} is regarded as both

• An 8-bit byte, that is, an element in the set and
• An integer in the set

Rijndael supports the Nk values of 4, 6, and 8 words (128, 192, and 256 bits).

The cipher key k is read into and from the array by columns from left to right

Plaintext ...