An introduction to cryptography

One of the most important things in cryptography is to understand definitions and notations. I have never been a fan of definitions and notations, first of all, because I am the only one to use notations that I've invented. But I realize that it is very important, especially when we are talking about something related to mathematics, to agree among ourselves. Thus, in this section, I will introduce basic information and citations relating to cryptography.We start with a definition of an algorithm.In mathematics and computer science, an algorithm is a finite sequence of well-defined computer-implementable instructions.An important question is: what is a cipher?A cipher is a system of any type able to transform plaintext (a message) into not-intelligible text (a ciphertext or cryptogram):

Figure 1.1 – Encryption process

To get some utility from a cipher, we have to set up two operations: encryption and decryption. In simpler terms, we have to...