Cryptosystem A cryptosystem is composed of a set Ee eEK) consisting of enciphering transformations and the corresponding set (Eel:ee)={Da:deX) of deciphering transformations.In other words,for each eK,there exists a unique deK such that Da=E,so that Da(Ee(m))=m for all mM. The keys (e,d)are called a key pair where possibly e=d.A cryptosystem is also called a cipher
Cryptosystem
问题3： 所谓“key”究竟是什么？
古典密码：德国陆军强于恺撒 The German ADFGVX Field Cipher A G X Plaintext:field cipher A B 3 D ↓ F H DF AX FG AV GF FA AX VX FX FG AG G ↓ key X R F L 5 3 2 4 D A X F G A G F 你试试： F A XFVAXAFFGXFFGXFXFXXGDXDAFGVA A G FFVGAVAXFAAFGXGXFDGFXA
古典密码：德国陆军强于恺撒 Plaintext: field cipher key 你试试：
问题4： 现在你能说清楚“钥”和 函数”之间的关系了吗
间题5： 你能香说说什么叫破解一个 密码系统？ 一个“好”的密码系统应该 是什么样的？