计算机问题求解一论题4-6 密码算法 2019年4月17日
计算机问题求解 – 论题4-6 - 密码算法 2019年4月17日
问题1： Cryptosystem是什么意思？它要解决 的基本问题是什么？
最古典：Caesar's Cipher Plain a b d e h k 1 m Cipher D E F G H K L M N P Plain n 0 P T t 心 U 0 E y Cipher Q R S T U W X Z A B a b c d e g h k m 0 1 2 3 4 5 6 7 8 9 10 11 12 m 0 p q r t u U U E y 2 13 14 15 16 17 18 19 20 21 22 23 24 25 Cipher=(Plain+3)mod 26 你试试：VKH GLH LV FDVW The die is cast
最古典: Caesar’s Cipher Cipher = (Plain + 3)mod 26 你试试: WKH GLH LV FDVW The die is cast
问题2： 你能不能用数学概念来描述加密和解密？
Transformations An enciphering transformation (also called an enciphering function)is a bijective function Ee MC, where the key e EK uniquely determines Ee acting upon plaintert message units m E M to get ciphertert message units Ee(m)=c∈C. A deciphering transformation (or deciphering function)is a bijective function Da:e→M, which is uniquely determined by a given key d E K,acting upon ciphertext message units c Ee to get plaintert message units Da(c)=m. The application of Ee to m,namely the operation Ee(m),is called enciphering, encoding,or encrypting m E M,whereas the application of Da to c is called deciphering,decoding,or decrypting ceC
Transformations