There are two main branches in the application of cryptography: 1) cryptography: it mainly studies the method of transforming information in the process of channel to protect it from being stolen, deciphered and used by opponents. 2) Password analysis: mainly study how to analyze and decipher passwords, also known as password attacks.

Passwords were originally used to encrypt information, and there are many cryptographic techniques in the computer field. However, with the application of cryptography, passwords are also used for identity authentication, denial prevention and other functions. Cryptography is an important secret means for communication parties to convert special information according to agreed rules. According to these laws, changing plaintext into ciphertext is called encryption transformation; Turning ciphertext into plaintext is called decryption transformation. In the early days, passwords only changed the encryption and decryption of characters or numbers. With the development of communication technology, voice, image and data can be encrypted and decrypted.

Cryptography is an ancient and profound subject, which is only used in a small range, such as military, diplomatic and intelligence departments. Computer cryptography is a science that studies the encryption, decryption and transformation of computer information. It is an interdisciplinary subject between mathematics and computer, and it is also a new subject. Cryptography is one of the main research directions of cyberspace security, and it is also the basis of many security mechanisms.