| With the advent of the 5G era,fast and secure data sharing in the cloud is attracting increasing attentions.In the proposed solutions,keyword search plays an important role because it can identify the user and search ciphertext without decryption.However,the existing searchable algorithms have many limitations,such as strong central authority,matching process only executes on the cloud server,easy to cause center corruption and single point of failure,making the fairness of keyword search still a challenge.In addition,with the continuous developments of the Internet and the gradual improvement of living standards,the security requirements for data sharing are no longer exclusive to special organizations.However,the existing research is mainly based on accurate search,which requires too much input when searching ciphertext,and fails in taking into account the differences of users resulting in non-standard input format and spelling errors.It leads to the great inconvenience for the users in the search ciphertext.Aiming at these problems,the main work of this thesis is as follows:1.A cloud-based multi-cloud and multi-authorization searchable encryption scheme based on blockchain is proposed.This scheme takes into account that the cloud server is not a completely trusted institution,and uses the public and immutable characteristics of blockchain to ensure the security of trap door matching while moving it to the blockchain,effectively preventing the problem of the cloud server not matching truthfully in order to save computing resources.At the same time,the solution adopts the multi-cloud block storage technology to store the ciphertext in the form of blocks on multiple cloud servers.The integrity and correctness of the returned ciphertext can be verified,which can ensure that the damage of a single cloud server will not affect the overall data.It can also prevent the cloud from sending relevant ciphertext falsely and users from making malicious accusations against the cloud due to the unidentifiable features of ciphertext,so as to make ciphertext retrieval fair and just.In addition,the scheme is implemented based on multi-attribute authorization authority.Each authorization center only manages a set of attributes and allocates a private key to the attribute.The final private key is synthesized by the user.The analysis of security and efficiency shows that this scheme can satisfy the security retrieval of cloud ciphertext and its efficiency is significantly improved.2.A multi-authorization multi-keyword hierarchical fuzzy search scheme based on blockchain is proposed.The solution based on precise search requires that the keywords entered in the search must be exactly the same as the pre-set keywords in ciphertext.Considering that data uploaders and downloaders do not contact each other during the sharing process,the query keywords are affected by the personal preferences and retrieval habits of data users,leading to certain differences in input,which causes inconvenience for data sharing.To solve this problem,this scheme proposes a multi-keyword fuzzy searchable encryption algorithm based on vector inner product.By comparing the similarity of key words to return ciphertext,it can effectively solve the retrieval difficulties caused by personal preferences or spelling mistakes of users,and expand the application range of searchable encryption.Meanwhile,the scheme takes into account that the shared data set can be classified according to attributes such as organization and discipline.By constructing access tree and authenticating the advanced attribute,the ciphertext set corresponding to the authenticated access tree can be retrieved,which can not only reduce the number of matches,but also prevent the user from wasting resources and risking ciphertext leakage caused by unauthorized ciphertext downloading.In addition,the solution also supports multiple authorization and allows ciphertext storage and trap matching to be separated,in the form of co-supervised trap matching on the blockchain.The efficiency analysis shows that this scheme has obvious improvement compared with similar schemes. |
