Cryptography is a science with a long history. In ancient times, passwords were used to transmit secret information. In modern wars, the transmission of information and the command of war are inseparable from passwords, and so is the diplomatic struggle. Passwords are generally used for the confidentiality of information communication transmission and storage. With the development of computer and information technology, the development of cryptography is also very rapid, and its application field is also expanding. Passwords are not only used for information encryption, but also for data information signature and security authentication.