The direct application of cryptography is to encrypt data and keep information confidential. In addition, cryptography can also be used to realize many aspects of information security, such as the integrity and indivisibility of information.

① Information authentication: to confirm the integrity of information, that is, the original message sent by the message sender has not been tampered with or forged by a third party during the message transmission.

② Protocol authentication: to confirm the authenticity of the subject, which is suitable for the first authentication of the system.

③ Digital signature: authenticate the source of data, verify whether the data has changed, and prevent the communication parties from cheating each other.

④ Public key infrastructure PKI: an information system that provides general security services for information security. KPI mainly includes CA, RA, certificate base, certificate management system, key management and other components.