1, the second floor points out the content of discrete mathematics, and the third floor makes sense, but it is biased.

Discrete mathematics is not directly related to cryptography, but it is necessary to study it, especially for information security majors.

There are many textbooks about cryptography, among which the classic is Principles and Practice of Cryptography (translated by Douglas R. Stinson Feng Dengguo). The knowledge of discrete mathematics does not affect the understanding of encryption algorithm. The basic courses of cryptography include number theory, algebra, finite fields and so on.

Many cryptographic algorithms, such as DES, can be understood without advanced mathematics knowledge. AES is a kind of block cipher, which requires a little knowledge of limited fields. Public key encryption and signature algorithms require knowledge of number theory.

You can't understand it, perhaps because you are a novice in this subject. You might as well read more articles, and your meaning will show.

Let's talk about the postgraduate entrance examination. If you take the cryptology exam in a professional course, I suggest you write an article on number theory first. Number theory is too important for cryptography. It is the cornerstone of public key cryptography and signature algorithm. Learn modern algebra properly and understand groups, rings and fields. Finite fields are also extremely important to cryptography, but for an undergraduate, it is enough to know finite fields.