Incremental efficient ciphertext retrieval method with dynamic time attribute control

Abstract

The application provides an incremental high-efficiency ciphertext retrieval method with dynamic time attribute control, wherein a data uploader is registered and authenticated by a time server, and the authenticated data uploader has the right to generate and upload an encrypted index and authorize others to search; a data user who needs to search ciphertext on a cloud server needs to apply to the data uploader for the right to search the ciphertext uploaded by the data uploader, and after obtaining the authorization of the data uploader, the data user receives an update voucher broadcast by the time server to update the authorization; the authenticated data uploader can set the access limit of the release time of the encrypted index according to the specific application requirement, and realizes the access control in the time dimension; the scheme has the full incremental property, and the communication and storage overheads are reduced compared with the previous schemes; the data availability is ensured while the user privacy and data privacy are protected.

Description

Technical Field

[0001] The present invention belongs to the field of computer application technology, and in particular relates to an incremental and efficient ciphertext retrieval method with dynamic time attribute control. Background Art

[0002] With the rapid development of cloud service technology, users and businesses are increasingly inclined to store their data on remote cloud servers. This has led to the development of numerous cloud-based applications, such as outsourced data storage and backup, cloud-based data hosting and synchronization, and cloud databases. However, while enjoying the convenience of cloud services, users and businesses are also increasingly exposed to potential threats. Since data owners lose physical control of their data after outsourcing it to cloud service providers, they can only blindly trust that cloud service providers will protect the privacy of their data. Contrary to expectations, numerous cloud service data breaches have occurred globally in recent years. To protect the privacy of outsourced data, encrypting it before uploading is a good approach, but this compromises data availability. To balance data confidentiality and availability while still enjoying the benefits of cloud services, searchable encryption has emerged.

[0003] Searchable encryption is a primitive whose encrypted ciphertext can be matched with a specific search trapdoor, thereby obtaining ciphertext containing specific information. If a general encryption scheme is used in a cloud service scenario, since ciphertext does not reveal the plaintext, after uploading a large amount of data to a cloud server, users who want to search for a keyword in the data must download the entire data from the cloud server to their local computer, decrypt it, and then search the plaintext. This inevitably incurs significant communication and computational overhead. If searchable encryption is employed, such as public key searchable encryption, the data user generates a public-private key pair and retains the private key. During the encryption process, the data uploader uses the public key to encrypt the keywords in the data, generating a searchable encrypted index, which is then uploaded to the cloud server along with the encrypted document. During the search process, the data user uses the private key to calculate a search trapdoor for the desired keyword and upload it to the cloud server. The cloud server uses the search trapdoor to search the encrypted index. If a match is found, the cloud server returns the corresponding ciphertext to the data user. Otherwise, the data user receives information that does not contain the keyword. Since the encrypted index does not leak information about related keywords, the search trap does not leak the request privacy of the data user, and the data uploaded by the data uploader is also encrypted, the server does not obtain relevant information about the data uploader and the data user, protecting data privacy while ensuring data availability.

[0004] Time is an important attribute in time-related scenarios. For example, in sealed auctions, encrypted bids cannot be decrypted until after the release time. Incorporating time-based access control into searchable encryption schemes allows for searches to be made only after the release time, which is of great significance and application. However, we cannot guarantee that users will search at the set release time. Therefore, existing searchable encryption schemes with time-release search control require all time credentials before the system time to be recorded in the cloud server so that users can search for documents with release times before the system time. This incurs a large amount of additional storage overhead and computational overhead due to traversing time credentials during searches. Furthermore, this approach does not support efficient modification of indexing strategies or revocation of user search capabilities during system operation. Summary of the Invention

[0005] The purpose of the present invention is to provide an incremental and efficient ciphertext retrieval method with dynamic time attribute control, aiming to improve the functionality and efficiency of existing ciphertext retrieval methods with time-release search control.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] An incremental and efficient ciphertext retrieval method with dynamic time attribute control comprises the following steps:

[0008] Step 1, initialization: the time server generates public parameters, a preset time tree, and the time server's public and private key pair, and the data user generates the data user's public and private key pair;

[0009] Step 2: The time server assists the data uploader in generating an encrypted index and search authorization, and sends them to the cloud server and authorized data users respectively;

[0010] Step 3: The data user receives the time information from the time server and generates a search trap based on the authorization and time information;

[0011] Step 4, search phase: the data user uploads the generated search trapdoor to the server, and the server performs the search process. If there is a matching result, the corresponding document is returned to the data user; otherwise, the information that there is no document related to the corresponding keyword in the database is returned;

[0012] Step 5, revocation phase: When the data user's search permission needs to be revoked, the time server assists the data uploader in generating a revocation certificate, uploads it to the cloud server, terminates the data user's search process, and revokes their search permission;

[0013] Step 6, extension phase: If the time space set during initialization is exhausted, the time server generates an extension credential and broadcasts it to the cloud server and data user. The cloud server and data user extend the ciphertext and authorized time space.

[0014] Furthermore, the step 2 specifically includes:

[0015] In step 2.1, the data uploader sends verification information and a blinded release time information set to the time server, i.e., the path of the release time in the time tree. The time server verifies the identity of the data uploader. If the verification is successful, the time server assists the data uploader in generating an initial authorization set for the release time based on the release time information set requested by the data uploader.

[0016] In step 2.2, the data uploader unblinds the initial authorization set, uses it as the set to be verified by the cryptographic dynamic accumulator, calculates the aggregate value, and uploads the aggregate value to the cloud server;

[0017] In step 2.3, the data user verifies the data uploader. If the verification is successful, the data uploader generates an authorization corresponding to the keyword and the relevant release time based on the deblinded initial authorization set, and sends the authorization to the data user.

[0018] Furthermore, the step 3 specifically includes:

[0019] Step 3.1: The time server uses the public parameters to calculate the update credentials for each time period and broadcasts them to the cloud server and all data users;

[0020] In step 3.2, the data user generates a search trapdoor after the release time and sends the search trapdoor to the server to search the encrypted index.

[0021] Furthermore, the sizes of the revocation certificate, the extension certificate, and the update certificate are constant.

[0022] Furthermore, generating a search trapdoor in step 3.2 specifically includes:

[0023] (1) The data user stays online, receives updated credentials at a specific time, and updates the authorization immediately after receiving the updated credentials; when a search is required, the latest authorization is used to generate a search trap;

[0024] (2) The data user goes online at a specific time and receives updated credentials. Only the credentials at the release time and the latest credentials received are retained. When a search is required, the retained credentials are used to update the authorization, and the latest authorization is used to generate a search trapdoor.

[0025] Furthermore, the step 5 specifically includes:

[0026] Step 5.1: The data uploader sends verification information, revocation type, and blinded revocation information to the time server. The time server verifies the identity of the data uploader and, if successful, assists the data uploader in generating an initial authorization set for revocation information based on the revocation information requested by the data uploader.

[0027] In step 5.2, the data uploader deblinds the initial authorization set, generates corresponding revocation certificates based on the content, and uploads them to the cloud server;

[0028] In step 5.3, the cloud server uses the revocation credentials to revoke the user's search capability or change the search strategy of the encrypted index.

[0029] Compared with the prior art, the present invention has the following positive effects:

[0030] 1. This invention provides a searchable encryption method with release time search control. Authenticated data uploaders can set release time access restrictions for encryption indexes based on specific application requirements, thus achieving time-dimensional access control.

[0031] 2. The present invention reduces the additional storage overhead caused by implementing time-release search control;

[0032] 3. The present invention realizes the functionality of permission revocation, policy modification, and time and space expansion;

[0033] 4. The present invention realizes the property of full increment. While ensuring functionality, the size of the certificate is constant, reducing communication overhead and the additional computing overhead brought by realizing functionality. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a system model diagram of a searchable encryption method with time dimension access control.

[0035] Figure 2 This is a flow chart of the program.

[0036] Figure 3 This is the flowchart of the revocation algorithm.

[0037] Figure 4 The flowchart of the extended algorithm. DETAILED DESCRIPTION

[0038] In order to make the above features and advantages of the present invention more clearly understood, the following examples are given and described in detail with reference to the accompanying drawings.

[0039] Please see Figure 1The incremental efficient ciphertext retrieval method of the present invention mainly includes four participating entities: time server, cloud server, data uploader and data user. Different entities have different functions and responsibilities.

[0040] The time server provides user authentication, assists in generating encrypted indexes and authorization, and publishes update services. It authenticates data uploaders and assists authenticated data uploaders in generating encrypted indexes and authorization, generates and broadcasts update credentials, assists in generating revocation credentials, and generates extended credentials.

[0041] The cloud server provides cloud storage and computing services, stores encrypted indexes and files, searches the encrypted indexes based on data users' requests, returns search results, and executes revocation and extension algorithms after receiving revocation and extension credentials.

[0042] The data uploader is the generator of private data and is a user authenticated by the time server. They can interact with the time server to generate encrypted indexes or revoke credentials and upload them to the cloud server (using the data user's private key and using an encryption algorithm to build encrypted indexes for keywords in the file, attaching release time attributes to these indexes and uploading them to the cloud server with the encrypted files);

[0043] Data users are users of private data and need to apply for search permissions for keywords from the data uploader. They need to receive update information broadcast by the time server at regular intervals, receive update credentials for updates after authorization, calculate the search trapdoor and upload it to the cloud server, and search the encrypted index in the cloud server after the corresponding release time.

[0044] In this encryption scheme, the time server registers and authenticates the data uploader. Authenticated data uploaders are granted the ability to generate and upload encrypted indexes and authorize others to search them. Data users who need to search ciphertext on the cloud server must request permission from the data uploader to search their uploaded ciphertext. After receiving authorization from the data uploader, the data user receives an update certificate broadcast by the time server to update their authorization.

[0045] When the scheme is running, we must ensure the security of some private data: when the time server assists the data uploader in generating the initial authorization set, the time server cannot know the information requested by the data uploader, that is, the requested keywords and the corresponding release time information; after the data uploader uploads the encrypted index to the cloud server, the cloud server cannot obtain the plaintext information corresponding to the encrypted index; the search trap generated by the data user will not leak any information about the relevant keywords; unauthorized users cannot collude with the cloud server to generate legal authorization; authorized users cannot effectively search the encrypted index before the release time; revocation credentials and extended credentials cannot be forged, otherwise the data stored in the cloud server may be maliciously tampered with.

[0046] Aiming at the different needs of four different participating roles and their possible malicious behaviors, the present invention designs an incremental and efficient ciphertext retrieval method with dynamic time attribute control, including the following steps:

[0047] Step 1: The time server generates public parameters, a preset time tree and a public-private key pair of the time server, and the data user generates a public-private key pair of the data user.

[0048] Step 2: The time server assists the data uploader in generating an encrypted index and search authorization, which are then sent to the cloud server and the authorized data user. The authorization process includes the following sub-steps:

[0049] In step 2.1, the data uploader sends verification information and a blinded set of release time information (i.e., the path of the release time in the time tree) to the time server. The time server verifies the identity of the data uploader. If the verification is successful, it assists the data uploader in generating an initial authorization set for the release time based on the release time information set requested by the data uploader.

[0050] In step 2.2, the data uploader unblinds the initial authorization set, uses it as the set that needs to be verified by the cryptographic dynamic accumulator to calculate the aggregate value, and uploads the aggregate value to the cloud server.

[0051] In step 2.3, the data user verifies the data uploader. If the verification is successful, the data uploader generates an authorization based on the unblinded initial authorization set, that is, the member certificate corresponding to the release time in the path, and sends the authorization to the data user.

[0052] Step 3: The data user receives the time information from the time server and generates a search trap based on the authorization and time information. The steps include:

[0053] In step 3.1, the time server uses the public parameters to calculate the update credentials for each period and broadcasts them to the cloud server and all data users.

[0054] In step 3.2, the data user can generate a trapdoor after the release time and send it to the server to search the encrypted index. The trapdoor generation algorithm is divided into two types according to different scenarios: (1) The data user remains online for a long time, receives updated credentials at a specific time, and updates the authorization immediately after receiving the updated credentials. When a search is required, the latest authorization is used to generate a search trapdoor. (2) The data user goes online at a specific time and receives updated credentials, retaining only the credentials at the release time and the latest credentials received. When a search is required, the retained credentials are used to update the authorization, and the latest authorization is used to generate a search trapdoor.

[0055] Step 4, search method, the data user uploads the generated search trap to the server, and the server executes the search process. If there is a matching result, the corresponding document is returned to the data user; otherwise, the information that there is no corresponding keyword-related document in the database is returned.

[0056] Step 5: During the operation of this solution, some data users may lose trust, and the data uploader may want to revoke their search permissions for certain keywords. Therefore, the solution provides a revocation method that can prevent the file from being indexed or revoke it until a later time. The time server helps the data uploader generate a revocation certificate and upload it to the cloud server. The generation process includes the following sub-steps:

[0057] In step 5.1, the data uploader sends verification information, the revocation type, and the blinded revocation information to the time server. This information is the path between the previous release time and the desired release time on the time tree. The time server verifies the data uploader's identity. If verification is successful, it assists the data uploader in generating an initial authorization set for the revocation information based on the requested revocation information.

[0058] In step 5.2, the data uploader deblinds the initial authorization set, generates corresponding revocation credentials based on the content, and uploads them to the cloud server.

[0059] In step 5.3, the cloud server uses the revocation credential to execute the revocation algorithm, revoking the user's search capability or changing the search strategy of the encrypted index.

[0060] Step 6, extension method, the time server generates an extended credential when the time space is exhausted and broadcasts it to the cloud server and data user. The cloud server and data user execute the extension algorithm to extend the ciphertext and the authorized time space.

[0061] This invention draws on the idea of ​​cryptographic dynamic accumulators: In terms of search, the search strategy (i.e., all time after the release time) is aggregated, reducing the additional storage overhead caused by the introduction of time-dimensional search control. In terms of functionality, because the scheme retains the computability of the encryption index, the data uploader can calculate the encrypted index using credentials and change the search strategy of the encrypted index to achieve the purpose of policy change, revocation, and time-space expansion. We use a full binary tree with post-order traversal to represent linear time space. This can represent system time while retaining minimal credentials, reducing the number of elements that may require membership proof, further reducing storage overhead and computational overhead during search. At the same time, the root node of the binary tree can be set as keyword information, binding the keyword information to the access strategy to prevent combination attacks.

[0062] In terms of security, the scheme's update credentials, revocation credentials, extension credentials, and authorizations are all impossible to forge. In terms of efficiency, the scheme achieves a fully incremental nature, that is, the size of the credentials is constant, and only entities holding authorizations or encryption indexes can perform update, revoke, extension, and search operations. For the search process, the update credentials ensure that the authorizations held by the user can be searched at any time after the release time, so that the time server does not need to save authorizations for all time periods, reducing the storage and computing overhead of the time server; for the revocation and extension functions, the data uploader does not need to recalculate the encryption index after the policy is changed, and the time server does not need to regenerate the system after the time space is exhausted, reducing the computing overhead required to implement the revocation and extension functions.

[0063] Example

[0064] An incremental and efficient ciphertext retrieval method with dynamic time attribute control is proposed. During initialization, the time server generates a public parameter pp according to the security parameter λ, and the time tree T and its public-private key pair (pk ts ,sk ts ), the data user generates his public-private key pair (pk u ,sk u After registering and authenticating with the time server, the data uploader can generate an encrypted index CT and corresponding authorization Aut about a specific keyword and its release time after interacting with the time server, and upload the ciphertext to the cloud server. The data user applies to the data uploader for search permissions for specific keywords, and the data uploader sends the corresponding authorization to the data user. The time server uses its own private key sk ts Calculate update certificate tkn updThe information broadcast by the time server is not related to the user's private information and is not generated for a specific user. Therefore, it can be broadcast publicly and any user can update their authorization by updating the certificate. The data user receives a specific update certificate to update the authorization. When searching, use the keyword W to be searched, the corresponding authorization Aut and their own private key sk u Generate search trapdoor Tr W The cloud server receives the search trapdoor and matches it with the encrypted index CT. If the corresponding keywords are the same and the current time is after the corresponding release time, the corresponding document is returned. In the revocation phase, the data uploader determines the keywords to be revoked and the time to be revoked, and interacts with the time server to generate the corresponding revocation certificate tkn re Upload to the cloud server, the cloud server executes the revocation algorithm to change the corresponding encryption index. In the extension phase, the time server determines the period that needs to be extended. When the period arrives, the time server uses its own private key sk ts Generate extended credentials.

[0065] The following is the algorithm process Figure 2 Further detailed description of the searchable encryption algorithm based on incremental time release:

[0066] 1. System initialization, the time server generates public parameters pp, time tree T, and generates the public and private key pair of the time server (pk ts ,sk ts ), the data user generates the public and private key pair (pk u ,sk u ).

[0067] 2. After the data uploader registers and authenticates with the time server, the data uploader will interact with the time server as follows:

[0068] a. The data uploader sets the release time t for the keyword W r , get t r All nodes on the path in the time tree. Calculate the blinded values ​​for all nodes and send them to the time server.

[0069] b. The time server uses its own private key sk ts Each blinded value is signed and the result is sent to the data uploader.

[0070] c. The data uploader receives the information and unblinds it, calculating its hash value H.

[0071] 3. The data uploader uses the data user's public key and the information obtained from interacting with the time server to calculate the encryption index CT and authorization Aut, uploads the encryption index to the cloud server, sends the authorization to the requesting data user, and retains information c about the encryption index random number and the data user's public key.

[0072] 4. The time server uses the private key sk ts Calculate the specific information of each period and calculate its hash value H t Broadcast to cloud servers and data users.

[0073] 5. Data users receive H t Calculate it with Aut to get the latest authorized Aut t .

[0074] 6. Data users use keyword W and private key sk u And the latest authorized Aut t Calculate the search trapdoor Tr W And upload it to the cloud server.

[0075] 7. The cloud server receives the search trap Tr W , run the search algorithm, obtain relevant documents containing keywords, and return the results to the data user.

[0076] The following is the algorithm process Figure 3 and Figure 4 Describe the revocation algorithm and extension algorithm in the scheme:

[0077] 8. The data uploader can choose two types of revocation according to their needs. If the index needs to be revoked to a certain time in the future, the keyword W to be revoked and the previous release time t are determined. r The time to cancel If the index needs to be completely revoked, a random number x is generated, blinded, and passed to the time server. The time server signs it and sends it to the data uploader. The data uploader unblinds the returned information and calculates the revocation certificate based on the retained information c associated with the keyword W and document D to be revoked. The revocation certificate is then uploaded to the cloud server. The cloud server executes the revocation algorithm and changes the information of the relevant encrypted index.

[0078] 9. After the current time reaches the right child node of the time tree root node, the time server uses its private key sk ts The extended credentials are calculated and broadcast to the cloud server and data users. The cloud server aggregates the extended credentials into the ciphertext to complete the ciphertext update. The user uses the extended credentials as the update credentials and updates the authorization according to the update phase method.

[0079] In the above scheme, the time server registers and authenticates the data uploader, restricting the data uploader to generate a valid encrypted index and granting the data uploader the ability to add time dimension access control and authorized user search permissions to the encrypted index.

[0080] This embodiment provides an incremental efficient ciphertext retrieval device, comprising: a memory, a processor, and a computer program stored in the memory, wherein the processor implements the steps of the incremental efficient ciphertext retrieval method when executing the computer program.

[0081] This embodiment provides a computer storage medium, wherein the computer storage medium stores an executable program, and the executable program is executed by a processor to implement the steps of the incremental efficient ciphertext retrieval method.

[0082] This invention proposes an efficient incremental ciphertext retrieval method with dynamic time attribute control. Data uploaders can encrypt files and set a keyword search release time based on their needs. This means that files related to the keyword can only be searched after this time. The encrypted files are then outsourced to a cloud server that provides cloud storage and computing services. Data users authorized to search for a keyword are then allowed to search for the keyword on the cloud server after the corresponding search release time. This approach allows for time-based access control of data users while ensuring data confidentiality and availability.

[0083] This method allows data uploaders to add dynamic time-based access control to encrypted indexes. This means that data users can only effectively search the encrypted index after a specified time point. Furthermore, this method supports data uploaders modifying the time access policy corresponding to an already generated encrypted index. This solution ensures data availability while protecting the privacy of uploaded data and user requests.

Claims

1. An incremental and efficient ciphertext retrieval method with dynamic time attribute control, characterized in that: Including steps: Step 1, initialization: the time server generates public parameters, a preset time tree, and the time server's public and private key pair, and the data user generates the data user's public and private key pair; Step 2: The time server assists the data uploader in generating an encrypted index and search authorization, and sends them to the cloud server and authorized data users respectively; Step 3: The data user receives the time information from the time server and generates a search trap based on the authorization and time information; Step 4, search phase: the data user uploads the generated search trapdoor to the server, and the server performs the search process. If there is a matching result, the corresponding document is returned to the data user; otherwise, the information that there is no document related to the corresponding keyword in the database is returned; Step 5, revocation phase: When the data user's search permission needs to be revoked, the time server assists the data uploader in generating a revocation certificate, uploads it to the cloud server, terminates the data user's search process, and revokes their search permission; Step 6, extension phase: If the time space set during initialization is exhausted, the time server generates an extension credential and broadcasts it to the cloud server and data user. The cloud server and data user extend the ciphertext and authorized time space.

2. The incremental efficient ciphertext retrieval method with dynamic time attribute control according to claim 1, characterized in that: The step 2 specifically includes: In step 2.1, the data uploader sends verification information and a blinded release time information set to the time server, i.e., the path of the release time in the time tree. The time server verifies the identity of the data uploader. If the verification is successful, the time server assists the data uploader in generating an initial authorization set for the release time based on the release time information set requested by the data uploader. In step 2.2, the data uploader unblinds the initial authorization set, uses it as the set to be verified by the cryptographic dynamic accumulator, calculates the aggregate value, and uploads the aggregate value to the cloud server; In step 2.3, the data user verifies the data uploader. If the verification is successful, the data uploader generates an authorization corresponding to the keyword and the relevant release time based on the deblinded initial authorization set, and sends the authorization to the data user.

3. The incremental efficient ciphertext retrieval method with dynamic time attribute control according to claim 1, characterized in that: The step 3 specifically includes: Step 3.1: The time server uses the public parameters to calculate the update credentials for each time period and broadcasts them to the cloud server and all data users; In step 3.2, the data user generates a search trapdoor after the release time and sends the search trapdoor to the server to search the encrypted index.

4. The incremental efficient ciphertext retrieval method with dynamic time attribute control according to claim 1, characterized in that: The sizes of the revocation certificate, extension certificate, and update certificate are constant.

5. The incremental efficient ciphertext retrieval method with dynamic time attribute control according to claim 1, characterized in that: Generating a search trapdoor in step 3.2 specifically includes: (1) The data user stays online, receives updated credentials at a specific time, and updates the authorization immediately after receiving the updated credentials; when a search is required, the latest authorization is used to generate a search trap; (2) The data user goes online at a specific time and receives updated credentials. Only the credentials at the release time and the latest credentials received are retained. When a search is required, the retained credentials are used to update the authorization, and the latest authorization is used to generate a search trapdoor.

6. The incremental efficient ciphertext retrieval method with dynamic time attribute control according to claim 1, characterized in that: The step 5 specifically includes: Step 5.1: The data uploader sends verification information, revocation type, and blinded revocation information to the time server. The time server verifies the identity of the data uploader and, if successful, assists the data uploader in generating an initial authorization set for revocation information based on the revocation information requested by the data uploader. In step 5.2, the data uploader deblinds the initial authorization set, generates corresponding revocation certificates based on the content, and uploads them to the cloud server; In step 5.3, the cloud server uses the revocation credentials to revoke the user's search capability or change the search strategy of the encrypted index.

7. An incremental and efficient ciphertext retrieval device, characterized in that: include: A memory, a processor, and a computer program stored in the memory, wherein when the processor executes the computer program, the steps of the incremental efficient ciphertext retrieval method according to any one of claims 1 to 6 are implemented.

8. A computer storage medium, characterized in that The computer storage medium stores an executable program, and the executable program is executed by a processor to implement the steps of the incremental efficient ciphertext retrieval method according to any one of claims 1 to 6.

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