问题9：monoalphabetic cryptosystems和 polyalphabetic cryptosysteml的区别是什么？ polyalphabetic cryptosystem letters.We can store a pair of letters pi and p2 in a vector p- Let A be a 2 x 2 invertible matrix with entries in Z26.We can define an encoding function by f(p)=Ap+b, where b is a fixed column vector and matrix operations are performed in Z26.The decoding function must be f-(p)=A-p-A-1b.问题9：monoalphabetic cryptosystems 和 polyalphabetic cryptosystem的区别是什么？ polyalphabetic cryptosystem