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README.txt

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Noekeon Block Cipher

Designers Joan Daemen, Michaël Peeters,
Gilles Van Assche, Vincent Rijmen
First published 2000-09
Derived from 3-Way, BaseKing
Key sizes 128 bits
Block sizes 128 bits
Rounds 16

Noekeon is a Substitution-Permutation Network operating on blocks of 128
bits using a 128-bits key. It operates on 4 words of 32 bits except for
the S-Box layer, "Gamma", which operates on 4-bits nibbles. The same
round key is used in every round; how it is derived depends on whether
related-key attacks must be considered or not. However, there exists
related-key differentials for both key schedules[96] It uses the
following operations.

Gamma: Consists in applying a 4-bit involution S-Box on nibbles
independently. Each of the 32 nibbles considered in Gamma is made of the
bits of index i in each of the 4 words for all i in [0, 31]. This leads
to a simple bitslice implementation of this layer. Most choices for
Gamma generated using the same design criteria would have lead to weak
ciphers but the one chosen in Noekeon does not[96]. Theta: A linear
layer which mixes words with each other and operates at the byte level.
It has a Lai-Massey structure where the Lai-Massey function is linear: x
\mapsto x \oplus (x <<< 8) \oplus (x >>> 8). The round key is XOR-ed
between the 2-steps of the Lai-Lassey operation. shift operations: Three
of the four words are rotated by different offsets, namely 1, 5 and 2.
Each rotations and their inverses are used.

A round constant is XOR-ed in the internal state before applying Gamma
during encryption. Since the components are involution-based, decryption
can be implemented using the same circuit as encryption. 16 rounds are
used.

It is claimed to be suitable for implementation in hardware and on 8-bit
processors.

The best attack by the designers is a linear attack based on a 2-rounds
iterative linear trail covering 9 rounds, which is then extended to
cover 12 rounds through key guessing.