Research And Implementation Of The Encryption And Ciphertext Query Of Cloud Storage Based On DAS Model

With the rapid development of the computer technology and applications,the amount of data of enterprise users is growing exponentially.And it has brought a sharp increase in costs for data storage and data maintenance which consumes the energy of the companies to a certain degree.They have to buy more hardware devices in order to expand the storage capacity.And even need to hire professionals to manage and maintain these data.To some extent,it limits the development of existing business.Thus,cloud storage service based on DAS model emerges.In this model,the client asks the third party DBSP to store and manage the sensitive data.However,the new storage model also brings new problems.Since the storage and access of data are dependent on the DBSP,enterprises are vulnerable to be attacked by the internal staff of the DBSP.If the data is not processed,they can easily get the data.So the client needs to encrypt the data before they are stored and managed by the DBSP.But the encrypted data lose the original similarity,order and comparability,which results in a significant decline in retrieval performance.Therefore,how to ensure data security in the premise,to improve ciphertext data retrieval performance is an urgent problem.The main research work is as follows:1.For numerical data,in the field of encryption,presented an improved encryption algorithm based on IDEA.Using the function to generate fixed range but random numbers,and adds the numbers to the multiples expanded original plaintext.So that the same value will be generated into different ciphertext after encryption.In the field of ciphertext query,presented an improved strategy in which the client first obtains the reference sequence of the distribution of values which is operated by the secure hash algorithm SHA-256 with the key.Then makes the original plaintext data map with the reference sequence.And stores the mapping result in the client database to prepare for late query.Then presented a range query strategy using numerical approximation strategy based on binary search.Compared with the original strategy,the query efficiency has been improved by using the core idea of binary search.2.For character data,in the field of encryption,presented an improved encryption algorithm based on IDEA.Using the function to generate fixed length but random character sequences,and used the sequences to be the header of the original plaintext.Through experiment,this encryption method has greatly improved the speed of encryption/decryption while ensuring the security.In the field of ciphertext query,presented an improved method of buckets partition which changes the characters into numerical values.And before the characters are divided into the buckets turns the IDs of the buckets into random numbers.Then divides random numbers of characters into the buckets while the numbers are generated by a random function.The characters are represented by the IDs of the buckets.Then the information of the characters are hided.At last,presented an improved index generating strategy which combines the generating strategy of the character set index based on BloomFilter and the generating strategy of the character position relation index based on dual encoding mapping function.Through experiment,the performance of this strategy of ciphertext query has been improved compared with the past ones.3.Based on DAS model,using the Ali cloud as the third party DBSP to store and manage the sensitive data.And has completed encryption and ciphertext query of character data using Java language in cloud storage environment based on DAS service model.Then gives a detail introduction of the code of the encryption/decryption module,character information hide module,character set features index generation module,character position relation features index generation module and ciphertext query module etc.And through experiments of encryption and ciphertext query,it has proved that the strategy has a higher retrieval performance while ensuring safety.