達到快速擴散的線性轉換

Abstract

擴散層是對稱性金鑰加解密演算法中重要的一部份，經由擴散層可以使得每一個明文或金鑰的輸入位元都有可能影響輸出密文的每一個位元，並且增加各種攻擊方法的困難度。 目前的對稱性金鑰加解密演算法的擴散層大多以線性轉換的方式來達成，在本篇論文中，我們提出一個能夠達到快速擴散效果的線性轉換，並且與 AES加解密演算法四個提案中的擴散層做一個評估與比較，我們的方法相較於其他演算法具有較快的擴散效果。

Diffusion layer is an important part of symmetric key block cipher. With the ability of diffusion layer, the change of every plaintext bit or every key bit affects every output bit. It also increases the difficulty of attack methods. The diffusion layer of most existing symmetric key block cipher is performed by linear transformation. In this thesis, a fast diffusion linear transformation is proposed. This approach enables symmetric key block cipher algorithm, after performing fewer rounds, to reach the desired results. We evaluate the byte diffusion order and bit diffusion degree of our method in compare with four AES proposals. The diffusion order of our method is 8. The diffusion degree of our method is 49 in worst case and is 64 in average case.