Cryptography originated from "crypt" in Greek kryptós and "writing" in gráphein. It is a subject that studies information security and confidentiality, involving cryptographic coding and cryptanalysis.

Cryptography has a long history, and its origin can be traced back to ancient Egypt, ancient Babylon, ancient Rome and ancient Greece thousands of years ago. According to China's ancient art classic "Liu Tao", as early as the Zhou Dynasty, there were two ways of keeping secrets: "Yin Fu" and "Yin Shu". Yin character is to make some bamboo pieces of different lengths in advance and agree on the content represented by each bamboo piece.

Because of the limited information conveyed by negative characters, a "negative book" appeared later, that is, the information was written in plain text on bamboo slips, and then the bamboo slips were randomly divided into three parts, each of which was given to a messenger. After the recipients have collected all the books, they can put these three "Yin Books" together and get the complete content.

The development of cryptography is generally divided into two stages: traditional cryptography and modern cryptography. The demarcation mark is Shannon's classic paper Communication Theory of Security System published in 1949.

Before that, in the traditional password stage with thousands of years' history, the password was mainly realized by substitution and substitution, and it was just an art of text transformation. Shannon introduced information theory into cryptography, which laid a solid theoretical foundation for cryptography and formed a scientific cryptography system.