Applied Cryptography Rearch For Outsourced Big-data Service Security And Privacy Protection

With recent advance in related technical and industrial areas,we have stepped into the era of big-data.The strategical significance of big-data technology lies in that,via specialized processing,it is feasible to explore the potential value implicitly contained in the massive data,so as to provide a reliable basis for analysis,forecasting and decision-making.Thus,bigdata-related industry has been paid special emphasis by national governments.However,data collection,cleaning,storage and analysis heavily depend on professional facilities,which is normally unaffordable for individuals and small enterprise for purchase and maintenance.Cloud computing,as a new service computing paradigm that provides users with convenient data storage,data processing,information sharing and virtualization services,has become ideal solution for large data engineering.Users can outsource their data to the cloud service providers,and latterly,retrieve the appropriate data according to their own requirements,or access to data-based services,this model is generally referred as outsourced computing.However,an important factor that restricts the popularity and proliferation of outsourced data services is the anxiety on data security and privacy.Especially in sensitive areas such as finance and healthcare,if data is compromised or leaked by cloud service providers,it will cause catastrophic damages to the users.Cryptography is a basic tool for data privacy insurance.Traditional encryption schemes can be used for ensuring data confidentiality,but encryption will impose restrictions on the data availability,which may disable the cloud's capabilities in processing,analysis and mining on the data.Thus,it is required to design new cryptographic primitives,which not only can protect data privacy,but also allow the cloud service provider to perform certain operation on the data.Searchable Encryption is a significant cryptographic primitive to insure storage security and data privacy in cloud computing environment.It allows a client to store a collection of encrypted documents on server;and latterly,according his specific search criteria,the client can perform keyword based searches and retrieve the documents,meanwhile ensuring that it reveals minimal information to the server.Early research on searchable encryption scheme mainly focused on efficiency,security and query expressiveness,whereas recently,the studies having been paid attention on searchable encryption that support dataset update dynamically.In this paper,we propose a new dynamic symmetric searchable encryption scheme.In the aspect of efficiency,the complexity of search algorithm is O(1),while file addition and deletion is 0(m"n)and O(N)respectively(here m" means the number of keywords in a document,N means the number of document-keyword pairs and n means the size of dictionary),which means the overall efficiency superior to the existing schemes;in the aspect of security,this scheme can resist selective keyword attack,and compared with former ones,it achieves less information leakage.One of the prominent deficiencies existed in current searchable encryption schemes is that most of the schemes regard keyword as query criteria.However,this manner is not applicable to agglutinative language corpus,because in this kind of language,the semantics is expressed by long strings composed of short morpheme.Thus,searching in such language should treat characters as basic unit.In this paper,we choose longest common substring as criterion for assessing the similarity of the string.Using somewhat homomorphic encryption as basic cryptography primitive we constructed the scheme to solve the longest common substring over encrypted data.Our scheme is of high efficiency and scalability.Implementation of this scheme only requires homomorphic circuits with logarithmic depth and only requires 0(?-1)log(?-1))homomorphic multiplication operation(in which ? is the length of bits used to encoding one character).As the basic component in privacy-preserving outsourced computing,our scheme will play a significant role in solving a wide range of concrete problems.