What is privacy protection? Privacy protection is a very complex concept, which usually refers to the protection of information that entities such as individuals or groups do not want to be known by outsiders. For individuals, an important type of privacy is personal identity information, that is, the use of this information can be directly or indirectly traced back to a certain person at a certain time and place through a connection query; for a collective , Privacy generally refers to sensitive information representing various behaviors of a group, that is, a group did something at a certain time and place [1].

There are many privacy protection technologies. For example, the privacy protection technologies for identity include obfuscation, group signature, blind signature, k-anonymity, differential privacy, multi-party secure computing and other technologies. Even the onion router tor belongs to an identity protection technology. Different privacy protection technologies solve privacy protection problems in different scenarios, and sometimes these technologies are used together