CN108111587B

CN108111587B - Cloud storage searching method based on time release

Info

Publication number: CN108111587B
Application number: CN201711344491.1A
Authority: CN
Inventors: 李会格; 张方国; 田海博
Original assignee: National Sun Yat Sen University
Current assignee: National Sun Yat Sen University
Priority date: 2017-12-15
Filing date: 2017-12-15
Publication date: 2020-11-06
Anticipated expiration: 2037-12-15
Also published as: CN108111587A

Abstract

The invention belongs to the field of cloud storage, and particularly relates to a cloud storage searching method based on time release. The invention stipulates the time authority for the plaintext data, and stores the plaintext data to the cloud after encryption processing. When a user wants to search a document, the server utilizes a search instruction generated by the user to search, and the server, the user and the time server interact with each other in the searching process to finally obtain a needed ciphertext file. And then the user and the time server continue to communicate to obtain a decryption key corresponding to the ciphertext, and the file is decrypted on line. The invention fully considers the requirement of the time consulting authority of the electronic document, ensures the privacy of the data and the time consulting authority, and has strong practicability.

Description

Cloud storage searching method based on time release

Technical Field

The invention belongs to the field of cloud storage, and particularly relates to a method for realizing searching on an encrypted electronic document in a certain time period in the future.

Background

With the rapid spread of the Internet, the storage of information has also moved from traditional paper archives to electronic archives using local physical disks. However, the society of today is an era of information explosion, and the storage amount of information is exponentially increased, which means that the costs for information maintenance and management, disk purchase and the like are continuously increased. On 9.8.2006, Google's first executive Auger, Schmidt (Eric Schmidt) first proposed the concept of "Cloud Computing" (Cloud Computing) at the search engine Congress (SES San Jose 2006). Then, amazon, microsoft, IBM, etc., have announced their respective cloud concept products-cloud storage.

The cloud storage refers to a system which integrates a large number of storage devices of various types in a network through application software to cooperatively work through functions such as cluster application, network technology or a distributed file system and provides data storage and service access functions to the outside. The system can reduce the local physical and cost expenses of the user, and the user really experiences the interest of inquiring personal data anytime and anywhere, so more and more users upload personal local data to the cloud. However, once the data is stored in the cloud, the user itself loses direct control of the data. Sensitive information in the data is often a target stolen by others, and in recent years, frequently-outbreak data leakage events make users more and more aware of the importance of guaranteeing data privacy and security.

The data are encrypted by using a cryptographic technology and then uploaded to the cloud, so that the privacy and the safety of the data are guaranteed to a certain extent, and the data query efficiency is influenced by the encryption technology. If the conventional encryption technology is adopted, the user needs to download all the cloud data, then decrypt the cloud data on the local server, and finally screen out the document set required by the user. Assuming that the fiber bandwidth used by the user is 100M, theoretically only 12.8Mb of files can be downloaded per second, and for 100G of data, it takes about 2 hours to completely download. Therefore, for light-weight data, the user can use this traditional search method, but this method is not practical when the data is large.

Song et al, 2000, proposed the concept of search encryption and presented a viable solution. The scheme mainly uses a pseudo-random function and a pseudo-random generator, in the process of executing search, a server needs to carry out bit-by-bit matching test on a search instruction and a ciphertext, and if the test is successful, the ciphertext is returned, so the search complexity of the protocol is O (n), wherein n is the length of a single document. Boneh et al introduced the concept of search encryption into the public key cryptosystem in 2003 and proposed a public key encryption search scheme (PEKS), so far, search encryption mainly includes two directions of public key search encryption and Symmetric Search Encryption (SSE). Generally, public key search encryption is powerful, but most PEKS schemes generally use bilinear pairs, so the search efficiency is not high. In the scheme of the SSE, the encryption and decryption keys of the users are the same, so that the SSE needs to broadcast the key to the users to realize the simultaneous uploading of documents by multiple users, which indirectly results in that the function of the SSE is not powerful enough, but the efficiency of the SSE is much higher than that of PEKS.

In SSE, there are mainly three participants: data owner U, server S and retrieval user U₁. Retrieving user U₁And the data owner U can be the same person or different, if U₁Different from U, then U₁The key K needs to be broadcast to U. The main ideas of SSE are: the data owner U uses the key K to change the local data D to (D)₁,D₂,…,D_n) Encrypted to C ═ C₁,C₂,…,C_n). Meanwhile, the data owner U creates an index table I for the data D, and finally the U stores C and I on the server S. Retrieving user U₁If a document containing a keyword w is to be queried, he first generates a search instruction t (w) for the keyword w by using the key K, and then sends t (w) to the server S. S finds out the pointer set of the document containing w in I through t (w), and then returns the corresponding ciphertext data to the user U according to the pointers₁. Finally, U₁The cryptograms are decrypted at the local device using the key K.

Early SSE schemes only supported precise searches for a single keyword, and later researchers extended the functions of SSE to some extent, such as fuzzy searches, range searches, subset searches, dynamic searches, ranking searches, sentence searches, and borolean searches. However, these functions have certain limitations and cannot solve the search problem in special occasions. For example, in the current SSE scheme, the time authority problem of the user for referring to the files is not considered, so that according to the current search mode, once the user performs a search, he will immediately obtain all the files required by himself. However, in many practical search problems, a time factor is considered.

For example, to avoid disputes between children and their own due to property segmentation, many merchants currently prescribe their own testimonials in advance and have lawyers manage the documents in a confidential manner. The order can only be opened at a specific time as specified. Since the existing encryption search technology cannot effectively solve such problems, the application range of the cloud storage technology is limited. For another example, in the electronic voting system, each voter anonymously uploads the voting result of the voter to the cloud. The candidate cannot know the ticket number of the candidate in advance, and only at the stage of disclosure, the candidate knows the total ticket number of the candidate. In fact, the search encryption technology based on time release is used in law offices and electronic voting systems, and has other application occasions, such as national examination result inquiry systems and the like.

At present, a method for solving the above problems is that an administrator uploads a file in the previous second of a specified time, however, this method is considerable for lightweight data, but when the file size is large and the number is large, network congestion is easily caused, and thus a user cannot obtain a corresponding query result at the first time. On the other hand, the existing technology does not consider the privacy of data, so that the potential of information leakage exists at any time.

In view of the above problems, it is desirable to provide a method for searching encrypted electronic documents in a specific time period.

Disclosure of Invention

In order to realize searching on the encrypted electronic document after a certain time point in the future, the invention provides a cloud storage searching method based on time release. Time release is an encryption algorithm based at some point in time in the future, the purpose of which is to ensure that encrypted information cannot be decrypted until a specified time.

The invention provides a cloud storage searching method based on time release, which comprises a data owner, a cloud server and a user;

the data owner is used for encrypting the local data and uploading the local data to the cloud server.

The cloud server is used for storing data and helping a user to search the data.

The method is characterized in that: the system also comprises a time server which is a trusted center;

mainly comprises the following steps:

(S1) the data owner inputs a system security parameter lambda to generate a key array used for encrypting the document and constructing the index, which is expressed as an n + 3-dimensional key

n is an integer of 1 or more, and represents the number of documents included in the document set D. The time server inputs a safety parameter lambda, randomly generates and broadcasts a series of public keys related to time; is shown as

And PK_1,1,…,PK_m,sM and s are integers which are more than or equal to 1, m is the number of keywords in the database, and the value of s depends on the maximum value of the number of the documents related to the keywords in the database.

(S2), the data owner sets the local document set D ═ D (D)₁,D₂,…,D_n) Encrypted ciphertext file set C ═ (C)₁,C₂,…,C_n). Meanwhile, the data owner creates an encryption index table I for the document set D, and the data owner stores the ciphertext document set C and the index table I to the cloud server. Wherein each document is represented as D_i(1 ≦ i ≦ n), and each ciphertext document is represented as: c_i(1≤i≤n)。

(S3), the legal user inquiry contains the key word w_α(1. ltoreq. alpha. ltoreq.m) using the key as the key word w_αGenerating a search instruction Tr (w)_α) Then search instruction Tr (w)_α) And sending the data to the cloud server.

(S4) the cloud server searches for the instruction Tr (w)_α) Finding the contained key word w in the index table I_αA set of pointers to a document

Since the cloud server does not have these file pointer sets

Corresponding decryption key SK_α,1,…,SK_α,sThe server needs to point these file pointers

And returned to the user. User receives file pointer set

And then communicates with the time server. The time server firstly verifies whether the identity information of the user is legal or not, and if so, the time server sends the corresponding decryption key { SK ] in a specified time period_α,1,…,SK_α,sAnd sending the data to the user safely. The user receives the decryption key SK_α,1,…,SK_α,sAfter, from the file pointer set

In-process decryption to obtain plaintext file identity identifier

The user communicates with the cloud server again and returns the corresponding ciphertext document

(S5), decryption stage: user receives ciphertext set

Thereafter, again communicate with the timeserver and obtain a corresponding decryption key from the timeserver

These keys are utilized by the end-user

Respectively for ciphertext

Decrypting to obtain corresponding plaintext information

In the step (S2), the data owner encrypts the document and establishes the index table by using a method of combining a symmetric encryption system and a public key encryption system, and finally generates a corresponding ciphertext and the index table.

Specifically, the process for the data owner to encrypt the document is as follows:

(S2 a.) data owner utilizes a key

Separately encrypting documents D₁,…,D_n：

I is more than or equal to 1 and less than or equal to n, wherein

Representing document D_iThe result of the corresponding encryption is that,

represents a symmetric encryption algorithm in which the encryption key used is

I is more than or equal to 1 and less than or equal to n. The data owner then chooses n time-dependent public keys

One-by-one pair of private keys used in encrypting documents

Carry out encryption, we denote by cki

The encryption result of (1):

here, the

Represents a public key encryption algorithm in which the encryption public key used is

Document D_iThe corresponding ciphertext is noted

User ciphertext C_i(i ═ 1, …, n) uploading to a cloud server;

specifically, the process of the data owner constructing the index table is as follows:

(S2b 1.) the data owner extracts a set of keywords W from the document set D₁,…,w_m}. Suppose each document D_i(1 ≦ i ≦ n) all have a unique ID id_i(i-1, …, n), which may be represented by a k-bit binary string. For each keyword w_le.W (l is 1, …, m), and selecting a null set D (W) with the size of s_l) And for the set D (w) as follows_l) Assigning values to the elements in (1): if document D_i(1. ltoreq. i. ltoreq. n) contains a keyword w_lThen document D is added_iCorresponding identity identifier id_iIs stored in D (w)_l) In (1). Order to

If D (w)_l) When the number of the elements in the series is less than s, s- | D (w) is randomly selected_l) The | k-bit binary string is padded with the symbol id'_j(id′_j≠id_j) Represents the corresponding identity identifier, where j ═ 1, …, s- | D (w)_l) L. Data owner using key K₁And a pseudo-random function F₁For each keyword w_l(l 1, …, m) the encryption process becomes t (w)_l)＝F₁(K₁,w_l) (l ═ 1, …, m). Suppose A is an m x s dimensional array initialized to empty, which is used to store D (w)_l) (l ═ 1, …, m) of each element. Specifically, the data owner is for each D (w)_l)(l＝1,…Id of element in m)_j(j is more than or equal to 1 and less than or equal to s) are encrypted one by one, and then the encryption results are stored in A (addr (N) in a linked list correlation mode respectively_l,1)),A(addr(N_l,2)),,…,A(addr(N_l,s) Therein addr (N)_l,1),addr(N_l,2),…,addr(N_l,s) Representing s different positions in the matrix a. The data owner selects a {0,1}^k×{0,1}^kAnd each key w in array A_l(l is more than or equal to 1 and less than or equal to m) corresponding to the position information addr (N) of the head node of the linked list_l,1) And t (w)_l) (1. ltoreq. l. ltoreq.m) is encrypted as (t (w)_l)，l(w_l)⊕addr(N_l,1) And stored in table T).

(S2b 2.) the index table I ═ a, T is uploaded to the cloud server.

The matrix a in the step (S2b1) is constructed as follows:

(S2b11). for D (w)_l) (1. ltoreq. l. ltoreq.m) each element id_jAnd (j is more than or equal to 1 and less than or equal to s) the encryption is carried out by utilizing the idea of combining symmetric encryption and public key encryption. Specifically, id for each element_jUsing a secret key K₃And a keyword w_lAnd (3) calculating:

(l is more than or equal to 1 and less than or equal to m, and j is more than or equal to 1 and less than or equal to s). Then, a symmetric encryption scheme is used, Enc (,) and

will id_jIs encrypted as

(l is more than or equal to 1 and less than or equal to m, and j is more than or equal to 1 and less than or equal to s). Selecting s public keys PK related to time from all public key sets published by cloud server_l,1,…,PK_l,sAnd using a public key encryption scheme₂Enc (·, ·,) encrypts keys used herein one by one

The corresponding ciphertext is noted

(j is more than or equal to 1 and less than or equal to s). Finally order

This value represents the element id_jThe result of the encryption. For each keyword w_l(l is more than or equal to 1 and less than or equal to m) s different empty positions addr (N) are randomly selected from A_l,1),…,addr(N_l,s) (1. ltoreq. l. ltoreq. m,) and information is expressed

(1. ltoreq. l.ltoreq.m, 1. ltoreq. j.ltoreq.s) are stored in the corresponding positions in sequence, where addr (N)_l,s+1) And ═ represents the end symbol of the read data and write data programs.

The table T in the step (S2b1) is configured as follows:

(S2b 12.) data owner utilizes a pseudo-random function F₁Secret key K₁,K₂For each keyword w_l(1. ltoreq. l. ltoreq.m): t (w)_l)＝F₁(K₁,w_l)，l(w_l)＝F₁(K₂,w_l). Then the array (t (w)_l)，

) Stored in the table T in a lexicographical ordering manner.

Specifically, the specific procedure of the step (S3) is as follows:

(S3 a.) user utilizes secret key (K)₁,K₂) For the keyword w desired to be inquired_αe.W generates a search instruction Tr (W)_α)＝(t(w_α),l(w_α),h(w_α))＝(F₁(K₁,w_α),F₁(K₂,w_α)，F₃(K₁,w_α) And sends it to the server, where t (w)_α) For searching for instruction Tr (w)_α) The first score in, l (w)_α) For searchingInstruction Tr (w)_α) The second score in (d), h (w)_α) For searching for instruction Tr (w)_α) The third score in (1).

Specifically, the step (S4) includes the following steps:

(S4a) the cloud server searches the instruction Tr (w)_α) First score t (w) of_α) Find the corresponding value in the table T

Then using Tr (w)_α) Second score of l (w)_α) XOR with γ to get the address addr (N)_α,1). The server extracts array A (addr (N)_α,1) Data stored in (c) in

Saving pointer information values of the first portion

And using Tr (w)_α) Third score h (w) of_α) And data

XOR to get addr (N)_α,2). Read array A (addr (N)_α,2) Data stored in (c) in

Saving pointer information values

Then using Tr (w)_α) Third score h (w) of_α) And data

XOR to get addr (N)_α,3). Repeat the above steps until the server encounters addr (N)_α,(s+1)) T ═ so long that the cloud server can obtain the pointer information in turn

(S4 b.) the cloud server assembles the pointer information in the last step

And returned to the user.

(S4c) the user receives the set of pointer information

Thereafter, it communicates with the time server in order to obtain the corresponding decryption key SK_α,1,…,SK_α,s。

(S4d) the user receives the decryption key SK released by the time server_α,j(t 1, …, s) and then use the key SK_α,jDecrypting array

The second component of

Then use

Decryption

The first component of

The user then continues to communicate with the cloud server.

(S4e) the cloud server receives the request of the user

Then, the corresponding ciphertext document is found out in C

And return it toA user.

The specific process of the step (S4c) is as follows:

(S4c1) the time server firstly verifies the identity information of the user, if the identity is legal, then checks whether the public key PK can be released currently_α,1,…,PK_α,sCorresponding private key SK_α,1,…,SK_α,s. If the private key SK can now be released_α,j(j is more than or equal to 1 and less than or equal to s), the value is sent to the user; if the specified time period is not reached, the private key SK is not returned_α,j(1≤j≤s)。

Specifically, the step (S5) includes the following steps:

(S5a) to be received by the user

Thereafter, the user continues to communicate with the time server to obtain the associated decryption key

The time server firstly verifies the identity information of the user, if the identity is legal, the time server checks whether the public key can be released currently

Corresponding decryption key

If so, the value is sent to the user. Herein, the

Is encryption

The public key used.

(S5b) the user receives the decryption key

Then, firstly, the

Second component ck α_jAnd (3) decryption:

then use

Decryption

First component of

Compared with the prior art, the invention has the following beneficial effects.

1. The privacy of the cloud documents is guaranteed. The plaintext data are encrypted and then stored in the cloud, so that on one hand, the privacy of the data is protected, on the other hand, convenience is brought to a user, and the user can inquire the own data on any equipment at any time and any place.

2. Data can be uploaded in advance, and the workload of a data owner is simplified. In the previous manner, the data owner needs to wait until the first second of a specific time to upload the document and is subject to network congestion during the process of uploading the document. The data is processed by utilizing an encryption mode of a time release mechanism, so that the data can be uploaded to the cloud in advance.

3. The time of the user query is normalized. Some data in actual life can only be inquired within a certain specified time period in the future, such as the leave orders, the national unified examination score inquiry and the like. The invention constructs an index related to time for the database, so that a user can only inquire the data set related to the key words in a specific time period.

Drawings

FIG. 1 is a system framework of the present invention.

Detailed Description

The technical solution of the present invention will be specifically described below by taking embodiment 1 as an example, with reference to the accompanying drawings. First we briefly describe the mathematical notation used.

_a＝(_a.Enc(·，·)，_aDec (·, ·,)) a secure cryptosystem algorithm, wherein_aEnc is the corresponding encryption algorithm,_adec is the corresponding decryption algorithm. When a is 1, the algorithm is a symmetric encryption algorithm, and when a is 2, the algorithm is a public key encryption algorithm.

-Enc (·,. Dec (·,)) determines a symmetric encryption algorithm, where Enc is the respective encryption algorithm and Dec is the corresponding decryption algorithm. The output length of the algorithm is k bits.

(PK, SK) a public-private key pair, where PK is the public key and SK is the corresponding private key.

F_b:{0,1}^k×{0,1}*→{0,1}^kPseudo-random function, b1, 2, 3.

π:{0,1}^k×{0,1}^k→{0,1}^kπ is the pseudo-random permutation of k-bit to k-bit.

D＝(D₁,D₂,…,D_n) A collection of documents.

D (w) a set of document identifiers comprising the keyword w.

W is a set of keys in D.

id_iIth document D_iAnd the corresponding file identifier consists of a k-bit binary character string.

A m · s.

addr(N_i,j) The addr (N) of the array A_i,j) Each position is represented by a k-bit binary string.

T{0,1}^k×{0,1}^kAn array of (2).

The number of elements in the set W.

Example 1

In this embodiment, a total of four participants are involved: data owner, cloud server, time server, user. The concrete implementation process comprises five links:

1. and a key generation stage: in this phase, the user enters a security parameter λ, generating an array of keys

And the time server inputs the security parameter lambda and broadcasts the public key to all members

And PK_1,1,…,PK_m,sThe private keys corresponding to these public keys are published to the legitimate users by the time server at a later specified time. The security parameter lambda takes a binary number of at least 256 bits.

2. And (3) an encryption stage: suppose a data owner has n documents D ═ D (D)₁,D₂,…,D_n) It needs to be uploaded to the cloud, for which he will complete the following two steps:

a) encrypt the document data. Data owner for each document D_iUsing cryptographic keys

Is encrypted, i.e.

Data owner selects public key

Pairing keys according to the idea of the public key cryptosystem

Carry out encryption

Final document D_iThe corresponding ciphertext is

b) Construct index table I. The data owner extracts the set of keywords W, assuming | W | ═ m. Then for each keyword w_lE.g. W, minSet D (w) of pairs_l) And (4) assignment is carried out: if document D_j(j ═ 1, …, n) contains a key w_l(l 1, …, m), then D is added_jDocument identifier id of_j(j ═ 1, …, n) is stored in set D (w)_l) In (1). Remember of s_l＝|D(w_l) 1 (…, m), and let

If D (w)_l) The number of the elements in (1) is less than s, then s-s is randomly selected_lA k-dimensional character string {0,1}^kD (w)_l) (l 1, …, m) is filled up to s elements. Let global variable ctr equal to 1, from keyword w₁Starting with the keyword w one by one_l(l ═ 1., m) the following is done:

I) calculate t (w)_l)←F₁(K₁,w_l)，l(w_l)←F₁(K₂,w_l)，

Will array (t (w)_l)，

) Stored in a dictionary ordering manner in a table T, where

Representing integer x by a pseudorandom permutation function

Mapping to the position of the addr (y) of the array A.

II) to D (w)_l) Each element in (1)

Selecting a time dependent public key PK_l,j(j ═ 1, …, s), and the following operations are performed:

and

and order

III) let ctr ═ ctr +1, calculate

Will be provided with

Is stored in array A (addr (N)_l,j) J ═ 1, …, s), where addr (N)_l,(s+1)) ═ denotes a null character, meaning the operation ends.

Let index table I equal (a, T), the data owner uploads ciphertexts C and I to the cloud.

3. A search instruction generation stage: when the user wants to inquire whether the keyword w is included_αThe user utilizes the key K₁,K₂For the keyword w_αCalculating t (w)_α)←F₁(K₁,w_α)，l(w_α)←F₁(K₂,w_α) And h (w)_α)←F₃(K₁,w_α). Let Tr (w)_α)＝(t(w_α),l(w_α),h(w_α) Is a search instruction and sends the value to the cloud server.

4. A search execution stage: when the cloud server receives a search instruction Tr (w) sent by a user_α) Then, it first uses t (w)_α) Found in Table T

Then by l (w)_α) To obtain

Read array A (addr (N)_α,1) Information in (2)

Storing information

Due to h (w)_α)＝F₃(K₁,w_α) So the cloud server can calculate

The cloud server continues to read A (addr (N)_α,2) Value in (1)

The above process is repeated until addr (N)_l,(s+1)) T, the cloud server may fetch in sequence

And returns it to the user.

User receives

Then sending the identity information to the time server, and once the verification is passed, the time server consults whether the public key PK can be released currently_α,j(j ═ 1, …, s) corresponding private key SK_α,1,…,SK_α,s. If the release is currently possible, the time server will use the corresponding private key SK_α,j(j is more than or equal to 1 and less than or equal to s) is returned to the user, if the private key SK is not allowed to be released currently_α,j(j is more than or equal to 1 and less than or equal to s), the value is not returned to the user.

User receives SK_α,j(j is not less than 1 and not more than s), and then using the value pair

Second component of

And (3) decryption:

(j is more than or equal to 1 and less than or equal to s). Then use

To corresponding

First component of

The following operations are performed:

user asks cloud server for

Corresponding ciphertext document

After receiving the instruction, the cloud server returns the corresponding ciphertext document

To the user.

5. And a decryption stage: user receives

Thereafter, the public key is again solicited from the time server

Corresponding decryption key

The time server responds to the user and combines

The corresponding decryption key is embedded in the time information according to the specified time

And sending the data to the user. End user receives

j is less than or equal to s), using these

To pair

Second component ck α_j(1. ltoreq. j. ltoreq. s) calculation

Then use

To corresponding

First component of

And (3) calculating:

(j is more than or equal to 1 and less than or equal to s). Eventually, the user gets the inclusion keyword w_αDocument of

The foregoing is only a preferred embodiment of the present invention, and it should be noted that those skilled in the art can make various improvements and modifications without departing from the principle of the present invention, and these improvements and modifications should also be construed as the protection scope of the present invention.

Claims

1. A cloud storage searching method based on time release mainly comprises a data owner, a cloud server and a user, and is characterized in that:

the system also comprises a time server which is a trusted center;

the method comprises the following steps:

(S1) the data owner inputs the security parameter lambda to generate a security key for encryptionKey array of documents and construction indexes, expressed as n +3 dimensional keys

n is an integer greater than or equal to 1 and represents the number of documents contained in the document set D; the time server inputs a safety parameter lambda, randomly generates and broadcasts a series of public keys related to time; is shown as

And PK_1,1,…,PK_m,sM and s are integers which are more than or equal to 1, m is the number of keywords in the database, and the value of s is determined by the maximum value of the number of documents related to the keywords in the database;

(S2), the data owner sets the local document set D ═ D (D)₁,D₂,…,D_n) Encrypted ciphertext file set C ═ (C)₁,C₂,…,C_n) (ii) a Meanwhile, the data owner creates an encryption index table I for the document set D, and the data owner stores the ciphertext document set C and the index table I to the cloud server; wherein each document is represented as D_i(1 ≦ i ≦ n), the corresponding ciphertext document is represented as: c_i(1≤i≤n)；

(S3), the legal user inquiry contains the key word w_α(1. ltoreq. alpha. ltoreq.m) document, the user first using the key as the keyword w_αGenerating a search instruction Tr (w)_α) Then search instruction Tr (w)_α) Sending the data to a cloud server;

The server needs to point these file pointers

Returning to the user; user receives file pointer set

Then communicating with a time server; after the time server verifies that the identity information of the user is legal, the corresponding decryption key SK is used in a future specified time period_α,1,…,SK_α,sSending to the user, the user receiving the decryption key SK_α,1,…,SK_α,sThen, from the file pointer set

In the clear text document identity identifier

The legal user communicates with the cloud server again and returns the corresponding ciphertext document

(S5), decryption stage: user receives cipher text document

Thereafter, communicating with the timeserver and obtaining a corresponding decryption key from the timeserver

The user utilizes these key pairs to encrypt the set of text

Decrypting to obtain corresponding plaintext information

2. The cloud storage searching method based on time release according to claim 1, wherein: in the step (S2), both the method of combining the symmetric encryption system and the public key encryption system is adopted when the data owner encrypts the document and generates the index table, and finally the ciphertext and the encrypted index table are generated.

3. The cloud storage searching method based on time release according to claim 2, wherein:

the specific process of encrypting the document by the data owner is as follows:

(S2 a.) data owner utilizes a key

Encrypted document D_i(1≤i≤n)：

Wherein

A symmetric encryption scheme is shown that is,

it is shown that the process of encryption,

which represents the process of decryption of the content,

indicating the keys used in the encryption and decryption processes,

representing the corresponding encryption result; then using n public keys related to time

Separately encrypting keys

Represents an encryption process of a public key encryption scheme using a public key of

Document D_iThe corresponding ciphertext document is

The data owner sets the ciphertext document set C ═ C (C)₁,…,C_n) Uploading to a cloud server;

the specific process of constructing the index table by the data owner is as follows:

(S2b 1.) the data owner extracts a set of keywords W from the set of documents D, and for each keyword W_lE.g. W (l ═ 1.., m), calculate D (W)_l) D (w) as defined above_l) Is composed of a key word w_lDocument D of_jIdentifier id of_jSet of constituent documents identifier id_jIs a binary string of k bits; data owner using key K₁And a pseudo-random function F₁Each keyword w_lIs encrypted into t (w)_l) (l ═ 1,. m); the data owner chooses an array A of dimensions | W | × s initialized to empty for storing D (W | ×)_l) (l ═ 1.., m) for each element; data owner first pair D (w)_l) Each element of (1., m)

The encryption process then stores these values in the addr (N) of matrix A in linked list association_l,1),…,addr(N_l,s) Position; if D (w)_l) When the number of elements in (l ═ 1., m) is less than s, the data owner randomly selects s- | D (w |, m)_l) Binary string of | k-dimensional bits

D (w)_l) Filling to s elements; the data owner selects one {0,1}^k×{0,1}^kAnd each key w in array A_l(l ═ 1.. multidata., m) of the head node position information addr (N) of the corresponding linked list_l,1) And a keyword w_lIs given by the cryptographic value t (w)_l) (l ═ 1.., m) is encrypted as

Then storing the result in a table T according to a dictionary sorting method;

the table T in the step (S2b1) is configured as follows:

(S2b 12.) data owner utilizes a pseudo-random function F₁Secret key K₁,K₂For each keyword w_l(1. ltoreq. l. ltoreq.m): t (w)_l)＝F₁(K₁,w_l)，l(w_l)＝F₁(K₂,w_l) (ii) a Then the array is

Storing the data in a table T according to a dictionary sorting method;

(S2b 2.) upload index table I ═ a, T to the cloud server.

4. The cloud storage searching method based on time release according to claim 3, wherein:

the matrix a in the step (S2b1) is constructed as follows:

(S2b11). first, for each D (w)_l) Each element id in (1., m)_j(j ═ 1.., s) as follows: using a secret key K₃And a keyword w_lAnd (3) calculating:

enc (·, ·) and

will id_j(1. ltoreq. j. ltoreq. s) is encrypted as

Selecting s time-dependent public keys PK_l,1,…,PK_l,sAnd using a public key encryption scheme₂Enc (·, ·,) encrypts keys used herein one by one

The corresponding ciphertext is noted

Finally order

The value is expressed as an element id_jThe encryption pointer value of (a); randomly selecting s different empty positions addr (N) in A_l,1),…,addr(N_l,s) Respectively transmit the information

Is stored in A (addr (N)_l,j) J is more than or equal to 1 and less than or equal to s); addr (N)_l,s+1) And ═ is used as the end symbol of the read data and the write data.

5. The time release-based cloud storage searching method according to claim 3 or 4, wherein: the specific process of the step (S3) is as follows:

(S3 a.) user utilizes secret key (K)₁,K₂) Keyword w queried for oneself_αGenerating a search instruction Tr (w)_α)＝(t(w_α),l(w_α),h(w_α) And sends it to the server; wherein t (w)_α) For searching for instruction Tr (w)_α) The first score in, l (w)_α) For searching for instruction Tr (w)_α) The second score in (d), h (w)_α) For searching for instruction Tr (w)_α) The third score in (1).

6. The cloud storage searching method based on time release according to claim 5, wherein: the specific process of the step (S4) is as follows:

Using Tr (w)_α) Second score of l (w)_α) Is transformed to gamma

Get the address addr (N)_α,1) The information of (a); the cloud server extracts array A (addr (N)_α,1) Data stored in (c) in

Saving pointer values in the data

Using Tr (w)_α) Third score h (w) of_α) For the above data

And (3) transformation:

obtaining addr (N)_α,2) (ii) a Repeating the above steps until the cloud server encounters addr (N)_α,(s+1)) Until ═ t, the cloud server can obtain the set of pointers in turn

(S4b) the cloud server sets the pointers in the step (S4a)

The value of (d) is returned to the user;

(S4c) user receipt

Thereafter, it communicates with the time server in order to obtain the corresponding decryption key SK_α,1,…,SK_α,s；

(S4d) the user receives the decryption key SK released by the time server_α,j(j is more than or equal to 1 and less than or equal to s), and then the key SK is utilized_α,j(j is more than or equal to 1 and less than or equal to s) decryption array

Is a second component value

By using

Decrypting array

Is measured at the first component value of

The user will

Sending the data to a cloud server;

(S4e) the cloud server receives the request of the user

Then, the corresponding ciphertext document is found out in C

And returns it to the user.

7. The cloud storage searching method based on time release according to claim 6, wherein:

the specific process of the step (S4c) is as follows:

(S4c1) the time server firstly verifies the identity information of the user, if the identity is legal, the public key PK is checked_α,1,…,PK_α,sThe release time of the corresponding private key; if the release of the private key SK is currently reached_α,1,…,SK_α,sThe corresponding private key SK_α,j(j is more than or equal to 1 and less than or equal to s) is sent to the user; if the specified time period is not reached, the private key SK is not returned_α,j(1≤j≤s)。

8. The time release-based cloud storage searching method according to claim 6 or 7, wherein: the specific process of the step (S5) is as follows:

(S5a) to be received by the user