## martes, 16 de octubre de 2012

### Algoritmos Bloque/Bloque ciphers

Who and Where?
The new Block Cipher Rainbow, is the title of an article written by Chang-Hyi Lee and Jeong-Soo Kim in the  Samsung Advance Institute of Technology.

Type of math
Where propose another model of Block Cipher. This type of cipher has the substitution and permutation. similar to the block ciphers Square and SHARK

Why?
In the article, the authors mention:
"the motivation for develop the algorithm came out from the hope that, first, the block cipher has the structure of parallelism, second, it has a self-reciprocal structure and third its round encryption  involves no linear and efficient key dependent diffusion layer".
The authors implement the algorithm and obtain that the proposal its acceptable, encrypting of 9 to 10mb/secs on a 133 MHz Pentium PC.

How it works?
This type of cipher works by 3 layers related to the round key active diffution and the others ones relates to the non linear sustitution with simple permutation.

G-Function
Where Xi are 32 bit subblocks and K be a 128 bit round key and  $\oplus$ denotes bit by bit logic XOR.

B-Function
Taking that x and k are the same that the previous.

Where ^ denotes bit by bit logic AND.

R-Function
This function consists in 3 types of components functions, P1, P2, P3, which all are defined in the following as functions of the sub-data block, GF(2³²) to GF(2³²). Let x = (x3, x2, x1, x0), Xi $\in$ GF(2⁸) and so x $\in$ GF(2³²). Let's define:

f be a bijective nonlinear function of GF(2⁸) to GF(2⁸)

f and f⁻¹ tables:

Performance: