Cryptography has been produced as early as 400 BC, and the history of human using passwords is almost as long as that of using words. The development of cryptography can be divided into four stages: ancient encryption methods. Classic password. Modern password. Modern password.

Cryptography (in Western European languages, it comes from the Greek words kryptós "hiding" and gráphein "writing") is a subject that studies how to secretly transmit information. In modern times, especially the mathematical research on information and its transmission is often regarded as a branch of mathematics and computer science, and it is also closely related to information theory.

In BC, secret letters were used in war. Herodotus, the father of western historiography, recorded some of the earliest secret stories in history. In the 5th century BC, in order to resist slavery and aggression, the Greek city-states had many conflicts and wars with Persia.

The development of cryptography can be roughly divided into three stages: classical cryptography, modern cryptography and modern cryptography. The classical cryptographic phase refers to a long time before the end of 19, and its basic feature is manual encryption and decryption.

Memorabilia of Historical Cryptography In the 5th century BC, primitive cryptographers appeared in Sparta, ancient Greece. A tape is wound around a wooden stick, and plain text is written along the longitudinal axis of the stick. There are only confused secret letters on the untied tape.