An Approach to Search for Multi-Round Differential Characteristics of Cypress-256
Mariia Rodinko, Roman Oliynykov · 2018
In this work it is considered the differential cryptanalysis of the lightweight block cipher Cypress that was recently developed in Ukraine. Firstly, a cryptanalysis model for Cypress block cipher is introduced. Then a method for searching for multi-round differential characteristics for Cypress-256 is proposed. The method includes the construction of a big set of one-round characteristics with further combination of them. The application of the proposed method reveled no match within the constructed set that is good for Cypress-256 from the point of view of its strength to differential cryptanalysis. The analysis of constructed set showed that inputs with the minimal Hemming weight are not always leads to high probable characteristics (especially, multi-round ones) and the most popular characteristics with a high probability have inputs with 5-6 active bits.