A Study of the Programmable Substitution-Permutation Cipher System

　　　　　本文使用可變替換盒及可程式化的交換盒設計密碼系統以改進傳統SP密碼系統之安全性。 我們使用新式交換盒的觀念設計一種可程式化的交換盒電路，使用密碼系統輸出密文的一個位元， 送入替換盒的移位暫存器以改變替換盒的金匙。此種密碼系統除了可程式化外亦可改變替換盒的金 匙，因此其安全性將較傳統僅可改變替換盒的密碼系統更安全。
　　　　　A technique for the variable substitution box and programmable permutation box was developed in this paper for improving the security of conventional SP ciphers. A hardware circuit of the new P-box was designed with this technique, and a new variable version of substitution box which takes one bit of output ciphertext and shifts into the S-box key shift registers to vary the S-box keys. The new SP cipher system is more secure than those conventional SP ones. Furthermore, the SP cipher system was observed as having regular, modular and local data communication features, which is well suited for VLSL implementation.