可抵禦明文攻擊的一種機制

Abstract

在本篇論文中，我們提出利用加入一個隨機變數和基底的轉換的機制對明文先做一個處理，使得在密碼系統中同樣的一個明文可以因此而產生出不同的密文。一方面因為隨機變數是不固定的，若其長度為r，則可產生出2|r|不同的隨機變數。另一方面，我們運用基底轉換的技巧打亂了原來的訊息。如此一來，讓攻擊者很難做攻擊。此外，在此篇論文中，我們另外將此種可抵禦明文攻擊的機制應用在DES和AES上。整個方法的安全性是建立於我們採用的區塊加密法DES或AES。本方法讓攻擊者更難攻擊，使得原有的DES或AES演算法擁有更進一步清楚而明確的安全性質。

In this thesis, we suggest a new method to add random number and convert among radices such as the fixed plaintext can produce more and different ciphertext in AES. On the one hand, because the random number is not fixed, that is to say, if the length of random number is r, then it can produce 2|r| different random number. On the other hand, we utilize the method of converting among radices to disarrange original message. Then, it is more difficult for an attacker. Furthermore, we apply this scheme to DES and AES in this thesis. The security of the whole scheme is based on the block cipher, AES and DES. Our method makes the attacker is difficult to decrypt, and that improve the original AES or DES algorithm to have more clear security properties.