System and method for utilizing offline electronic portfolio based on pdf security mechanism

Abstract

The application discloses a method for utilizing offline electronic archives based on a PDF security mechanism, and comprises the following steps: when an archive management system receives an application for utilizing archives offline, the archive management system generates an offline copy file of the electronic archives, and approves and sets access control permissions; the access control permissions of the electronic archives are written into the security mechanism of the PDF copy file, the utilization permissions of the offline copy file of the archives are set, a specified archive offline reader opens the offline copy file, the access control metadata objects in an access control table are inquired, and the utilization of the offline copy file of the electronic archives by the offline reader is controlled according to the utilization permissions in the metadata objects.

Description

Technical Field

[0001] This invention relates to the field of electronic document and information security technology, and is a protection technology for offline use of electronic archives, specifically a protection method for offline use of electronic archives based on PDF security mechanism extensions. Background Technology

[0002] Currently, in the process of offline sharing and utilization of electronic archives, electronic archives are usually generated as PDF format archive copies. Security behavior controls are added to the archive copies (such as: opening password, whether printing is allowed, whether editing is allowed) before downloading or copying to local devices for subsequent use. Generally, this only solves the problem of "who can view it", but it cannot control how to further restrict the viewing process, or how the behavior is controlled after viewing. It is also impossible to control whether the downloaded copy can still be viewed after the utilization period expires, or whether it is destroyed regularly after viewing. Therefore, there is a great risk of file leakage in the offline utilization of electronic archives.

[0003] Publication No.: CN 117609967, Title: "An Application of Anti-proliferation Technology in Document Preview Permissions". This paper provides a method for applying anti-proliferation technology to document preview permissions. By using digital encryption and anti-proliferation watermarking techniques, it achieves secure reading and use of documents. This method can restrict unauthorized use of document information and significantly reduce the risk of document dissemination.

[0004] In conclusion, the offline use of electronic archives urgently requires a method for secure access control of electronic documents to effectively address the issues of preventing leakage, dissemination, and tampering during offline use. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides a method for protecting offline access to electronic archives based on an extension of the PDF security mechanism. By setting security policies for offline electronic archive files, the requirements for access control of electronic archives are written into the security mechanism of PDF files. Then, by controlling the operation of archive copy files through an offline archive reader, the leakage, dissemination, and tampering of archive information can be prevented.

[0006] Based on the first aspect of this invention, a system for utilizing offline electronic archive files based on a PDF security mechanism is proposed. The archive management system verifies the identity of the offline archive reader and sets access control permissions upon receiving an application for offline access to the archive, generates an offline copy file of the electronic archive, and writes the access control permissions for offline access to the electronic archive into the offline copy file. The offline archive reader that passes the verification obtains the offline copy file, reads the access control metadata structure table of the offline copy file, obtains the access control permissions for the offline copy file, and controls the use of the offline copy file according to the access control permissions.

[0007] Further preferably, the generation of offline copy files of electronic archives includes: the archive management system generating PDF documents from the electronic archive files that have been approved for use, setting offline access permissions and generating watermark information, and writing the watermark information and access control permissions into the PDF copy file.

[0008] Further preferably, the step of writing access control permissions into the PDF copy file includes: encrypting the access control metadata table, writing it as an object to the end of the PDF archive file, adding a file access control metadata object that records document access control items to the end of the PDF document, and generating an archive copy file.

[0009] Further preferably, the step of writing the object to the end of the PDF archive file includes: encrypting the access control metadata in the access control metadata table to obtain a series of ciphertext values ​​(C1, C2...C...). n The obtained ciphertext value and the offline reader's special identifier are combined into extended data. The extended data and the end of the electronic document PDF file are merged to obtain merge information. The hash value of the merge information is calculated, and the hash value is digitally signed. The hash value of the digital signature is placed before the end identifier of the PDF document.

[0010] Further optimization includes document access control items such as: password for opening offline copy files, number of openings, opening time limit, copy control, save as control, print control, and hardware binding. Each time the offline file reader opens an offline copy file, it reads the access control metadata, reads the access control metadata object at the end of the file, decrypts the metadata value using a key, obtains the offline file reader's unique identifier and access control list, obtains operation control permissions, calculates the number of openings, and then encrypts and updates the access control metadata object.

[0011] Further optimization involves the offline reader opening a PDF copy file, reading the PDF file's access control object metadata, accessing the access control metadata structure table using a key, decrypting and reading the open password field of each metadata element in the access control metadata structure table using the AES-256 algorithm, and reading the function control fields respectively. The offline reader controls the utilization behavior of the offline copy file based on the content of the control fields.

[0012] Based on the second aspect of this application, a method for utilizing offline electronic archival files based on a PDF security mechanism is proposed. The method includes: a record management system, upon receiving an application for offline access to records, verifying the identity of the offline record reader and setting access control permissions, generating an offline copy of the electronic record, and writing the access control permissions for offline access to the offline copy file; an approved offline record reader acquiring the offline copy file, reading the access control metadata structure table of the offline copy file, obtaining the access control permissions for the offline copy file, and controlling the utilization of the offline copy file according to the access control permissions.

[0013] Further preferably, generating an offline copy of the electronic archive includes: the archive management system generating a PDF document from the electronic archive file that has been approved for use, setting offline access permissions and generating watermark information, and writing the watermark information and access control permissions into the PDF copy file; the step of writing access control permissions into the PDF copy file includes: encrypting the access control metadata table, writing it as an object at the end of the PDF archive file, adding a file access control metadata object that records document access control items at the end of the PDF document, and generating the archive copy file.

[0014] Further preferably, the step of writing the object to the end of the PDF archive file includes: encrypting the access control metadata in the access control metadata table to obtain a series of ciphertext values ​​(C1, C2...C...). n The obtained ciphertext value and the offline reader's special identifier are combined into extended data. The extended data and the end of the electronic document PDF file are merged to obtain merge information. The hash value of the merge information is calculated, and the hash value is digitally signed. The hash value of the digital signature is placed before the end identifier of the PDF document.

[0015] Further optimization involves the offline reader opening a PDF copy file, reading the PDF file's access control object metadata, accessing the access control metadata structure table using a key, decrypting and reading the open password field of each metadata element in the access control metadata structure table using the AES-256 algorithm, and reading the function control fields respectively. The offline reader controls the utilization behavior of the offline copy file based on the content of the control fields.

[0016] This invention effectively manages and restricts downloaded or copied archive copies for subsequent use by adding security behavior controls to archive copies. It establishes security policies for files, incorporating electronic archive access control requirements into the security mechanism of PDF files. Furthermore, it controls the operation of archive copies through an offline archive reader, thus preventing the leakage, dissemination, and tampering of archival information. This not only solves the problem of "who can view" but also how to use them, managing and controlling the reading targets, time, frequency, copying, printing, and saving capabilities of offline electronic archive files, thereby mitigating the risks of file leakage and expansion of information during offline use of electronic archive files. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the overall business process for offline file utilization in this exemplary embodiment;

[0018] Figure 2 This exemplary embodiment illustrates the generation of a copy file for the access control metadata object.

[0019] Figure 3 This is a schematic diagram of the offline reader access control flow in this exemplary embodiment. Detailed Implementation

[0020] This invention provides a protection method for offline use of electronic archives based on PDF security mechanism extension. By setting security policies for files, the requirements for access control of electronic archives are written into the security mechanism of PDF files. Then, by controlling the operation of archive copy files through an offline archive reader, the leakage, dissemination and tampering of archive information can be prevented.

[0021] like Figure 1 The diagram illustrates the overall business process for offline document utilization in this exemplary embodiment. The document management system generates PDF format electronic offline copies of the documents, establishes a security mechanism to write the electronic document access control table into the PDF copy file, sets utilization permissions for the offline copy file, and when the document management system receives an offline utilization request, the designated offline reader opens the offline copy file, queries the access control metadata object in the access control table, and controls the offline reader to utilize the electronic document offline copy file based on the utilization permissions in the metadata object.

[0022] Application for Offline Access to Archives. The archive user searches for the archive they need based on the archive number and other information, fills out and submits the archive access application information, which includes the access method, access time, purpose and other information.

[0023] If a user of an employee's personnel file requests access to a pre-employment training plan and training materials, the system will search for the location of the training plan and materials, the current status and usage of the personnel file, access permissions, and whether approval is required.

[0024] Offline access approval for archives. For archives requiring approval, archive management personnel approve electronic archive access applications, review access information, and set access permissions and time limits for offline access to electronic archives. Specifically, this may involve setting corresponding file operation control permissions for offline electronic archive copies (such as setting open passwords, number of open attempts, open time limits, copy control, save as control, print control, hardware binding, etc.).

[0025] For example, setting permissions for offline copies of archives includes: setting the password to open the offline copy file, the number of times it can be opened, the validity period, the device to open it (specified terminal or all terminals), whether to allow printing, saving, saving as, copying, and screenshotting of the file, and the name of the user of the offline archive, etc.

[0026] Document copy generation. The document management system packages the electronic documents involved in the approved electronic documents into a single PDF document for use. The document generation process includes: generating watermark information based on the applicant, the validity period of the copy, and usage permissions; writing the watermark information into the PDF file of the electronic document to be used; and encrypting all access control permissions set during the approval process before writing them into the PDF file. PDF file encryption ensures that the file can only be parsed using a designated offline document reader.

[0027] Specifically, a file access control metadata object is added to the end of the PDF document to record document access control items. These items include: password for opening PDF copies, number of opening attempts, opening time limit, copy control, save as control, print control, and hardware binding permissions. Each time the offline electronic document reader opens a document, it reads the access control metadata, decrypts it using a key, calculates the access count, and then encrypts and updates it to the access control metadata object.

[0028] First, the access control metadata table is encrypted and written as an object to the end of the PDF archive file, generating a copy of the archive file. The encrypted metadata in the access control metadata table yields a series of ciphertext values ​​(C1, C2...C...). n The obtained ciphertext value and the offline reader's unique identifier are combined into extended data. The extended data and the end of the electronic document PDF file are merged to obtain merged information. The hash value of the merged information is calculated and digitally signed.

[0029] File copy and access control permission parsing. When the offline file reader needs to open an offline file, the structure of the offline file PDF document is first parsed, the access control metadata object at the end of the file is read, the metadata value is decrypted using a key, the offline file reader's unique identifier and access control list are obtained, and operation control permissions are acquired.

[0030] Using the above method, when it is necessary to download electronic archive files for offline use, a dedicated offline archive reader is secured by verifying the digital signature information at the end of the PDF file, as well as its access control permissions, to prevent unauthorized readers from obtaining offline archive files and to further control the operation and processing of offline electronic archive files.

[0031] A timestamp can be added during signing to support signature time verification for subsequent use of electronic documents. The signature value can be placed between the merged information and the offline electronic document's end identifier.

[0032] Access counts are updated in real time, and encryption and signatures ensure that the file access control metadata object itself is immutable.

[0033] Design an access control metadata object and embed it into the metadata of the PDF document. Use a unique identifier to associate it with the PDF copy document. The metadata object includes: opening password, allowed number of openings, number of times it has been opened, validity period, copy control, printing control, and save as control.

[0034] like Figure 2 The diagram illustrates the generation of a copy file for the added access control metadata object.

[0035] Generate a copy of the archive file. Encrypt the access control metadata structure table and append it to the end of the electronic archive file (PDF) file structure.

[0036] Construct an access control metadata structure table including names and values ​​(as shown in Table 1), encrypt the access control metadata, write it as an object into the electronic archive PDF copy file, and generate the archive copy file.

[0037] Table 1: Access Control Metadata Structure Table

[0038] Serial Number Access control metadata name Access control metadata 1 Open Password 12345678 2 Allowed number of times to open 3 3 Number of times opened 1 4 Document validity period 2024 / 2 / 1 / 23:59 5 Copy control Allow / Prohibit 6 Save control Allow / Prohibit 7 Save As Control Allow / Prohibit 8 Printing control Allow / Prohibit 9 Screenshot control Allow / Prohibit 10 Equipment control Bse72u 11 CPU serial number Bse72u

[0039] Encryption of access control metadata can be achieved through encryption protection and digital signatures. An access password can be set for the access control metadata structure table to ensure that the access control metadata can only be decrypted by a dedicated file reader. Digital signatures can be used to sign the access control metadata.

[0040] Encryption protection: Access control metadata or source data tables can be encrypted using the AES-256 encryption algorithm, ensuring that the metadata values ​​can only be decrypted and modified by an offline file reader.

[0041] Signature mechanism: Digitally sign access control metadata to ensure its integrity and prevent unauthorized tampering. Signatures can be verified using PKI (Public Key Infrastructure) technology.

[0042] Downloading document copies. After the document access application is approved, the document management system checks the user's device operating system (Windows, Linux, Android), selects the format corresponding to the operating system, and downloads the approved document copy along with a PDF offline reader to the user's device.

[0043] Offline document reader detection. When a copy of a document is opened, the document management system verifies the key to check if it is accessed by an offline document reader. If it is, the system grants permission to open the access control metadata structure table and reads the access control metadata from it, thus granting permission to open the copy of the document. If it is not accessed by an offline document reader, the document management system denies access to the copy of the document and prompts "Please download a dedicated offline document reader".

[0044] like Figure 3 The diagram illustrates the access control implementation process in this exemplary embodiment. It includes: an offline reader opening a PDF file copy, parsing the file structure, determining whether the offline reader used to open the file is a dedicated reader for that file copy based on a key; if so, the dedicated reader parses the file structure, reads the PDF file's "Access Control" object metadata, reads the open password field from the object metadata, compares the open password with the user-input password, authenticates the user, reads the allowed number of openings field, reads the number of times already opened, and compares it with the allowed number of openings in the object metadata. If the number is less than the allowed number of openings, the offline reader reads the file copy document validity period control field, reads the current system time, and compares whether the current time is greater than the validity period. If it is less than the validity period, the offline reader reads the copy control field; if the copy content control field is prohibited, the offline reader controls the copy operation; reads the print control field; if the print control field is prohibited, the offline reader controls printing; reads the save as control field; if the save as control field is prohibited, the offline reader controls saving the file copy; and reads the save control field; if the save control field is prohibited, the offline reader controls saving. When the number of allowed openings or the validity period of the file copy is exceeded, the offline reader is prohibited from opening the file copy.

[0045] Control measures include:

[0046] (1) Open Password: The offline file reader reads the "Open Password" field in the file access control metadata object. If the value is not empty, it retrieves the value of the field. The offline reader pops up a password input box, and the user enters the password characters. The entered characters are encrypted using the MD5 algorithm and then compared with the value of the "Open Password" field. If the characters match, the offline file reader is allowed to open the offline file and proceed to the next verification step.

[0047] (2) Opening count control: The offline file reader reads the “Allowed opening count” and “Opened count” fields from the file access control metadata object, obtains the corresponding field values, and compares them with the opening count and opened count of the copy file. If the opened count is greater than the allowed opening count, the file management system sends a “This file has exceeded the allowed access count and is not allowed to be accessed” reminder. When the opening count is greater than the allowed opening count, the offline reader parses and displays the file content according to the PDF parsing standard, and at the same time increments the opened count by 1 and encrypts it using the AES-256 encryption algorithm before writing it back to the “Opened count” field in the metadata object.

[0048] (2) Validity period control: When the offline reader opens a copy of the file, it first accesses a time server on the Internet to obtain the current operation time. If the Internet cannot be accessed, the operating system time is used as the current time. The "Document Validity Period" field is extracted from the metadata object of the file access control. The corresponding field value is read and compared with the current time. If the current time is greater than the document validity period, a "This file has exceeded its validity period and access is not allowed" reminder is sent. If the current time is less than the document validity period, the offline reader then parses and displays the content of the file according to the PDF parsing standard.

[0049] (3) Copy control: Read the “Copy control” field in the metadata object of access control. If the field value is prohibited, the offline reader issues a disable command to disable the “Ctrl+C” and copy button functions of the operating system, and at the same time disable the “copy” function button of the right mouse button to restrict the copying of file content and prevent leakage and dissemination.

[0050] (4) Save control: Read the "Save control" field in the metadata object of access control. If the field value is prohibited, set the save button of the file to be disabled to control the modification of the file content.

[0051] (5) Save As Control: Read the “Save As Control” field in the metadata object of access control. If the field value is prohibited, disable the save as button for the file to prevent the user from saving it as another file.

[0052] (6) Print control: Read the “Print control” field in the metadata object of access control. If the field value is prohibited, disable the file print button to prevent leakage through paper.

[0053] (6) Open Device: Read the "Open Device" field from the access control metadata object. If the field value is not empty, it needs to be opened under specified settings. Read the CPU serial number of the current computer through an offline reader. If the field value matches the CPU serial number of the specified device, allow the device to open the file copy. Compare it with the "CPU Serial Number" field value in the metadata object. If the field value does not match the CPU serial number of the current computer, remind the user that "this file is not allowed to be accessed outside the specified computer". If they match, display the file content.

[0054] (8) Screenshot control: Read the “screenshot control” field in the metadata object of access control. If the field value is prohibited, the offline file reader monitors the keyboard and mouse events of the operating system. When the mouse moves out of the file content display area of ​​the reader or a key is pressed, the file content is masked with a mask. After the mask is applied, the mouse moves back to the mask page and clicks to hide the mask page again and display the file content again to prevent leakage and dissemination.

Claims

1. A system for utilizing offline electronic archive files based on PDF security mechanisms, characterized in that, The document management system verifies the identity of the offline document reader and sets access control permissions based on the received application for offline document access, generates an offline copy of the electronic document, and writes the access control permissions for offline access of the electronic document into the offline copy file; Once approved, the offline document reader acquires an offline copy file, reads the access control metadata structure table of the offline copy file, obtains the access control permissions for that offline copy file, and controls the use of the offline copy file based on the access control permissions. Document access control items include: offline copy file opening password, number of openings, opening time limit, copy control, save as control, print control, and hardware binding. Each time the offline document reader opens an offline copy file, it reads the access control metadata, reads the access control metadata object at the end of the file, decrypts the metadata value using a key, obtains the offline document reader's unique identifier and access control list, acquires operation control permissions, calculates the number of openings, and then encrypts and updates the access control metadata object.

2. The system according to claim 1, characterized in that, The process of generating an offline copy of an electronic archive includes: the archive management system generating a PDF document from the electronic archive files that have been approved for use, setting offline access permissions and generating watermark information, and writing the watermark information and access control permissions into the PDF copy file.

3. The system according to claim 2, characterized in that, Writing access control permissions to a PDF copy file includes: encrypting the access control metadata table, writing it as an object to the end of the PDF archive file, adding a file access control metadata object recording document access control items to the end of the PDF document, and generating an archive copy file.

4. The system according to claim 3, characterized in that, The step of writing the object to the end of the PDF archive file includes: encrypting the access control metadata in the access control metadata table to obtain a series of ciphertext values ​​( , ... The obtained ciphertext value and the offline reader's special identifier are combined into extended data. The extended data and the end of the electronic document PDF file are merged to obtain merge information. The hash value of the merge information is calculated, and the hash value is digitally signed. The hash value of the digital signature is placed before the end identifier of the PDF document.

5. The system according to any one of claims 1-4, characterized in that, The offline reader opens a PDF copy file, reads the access control object metadata of the PDF file, accesses the access control metadata structure table using a key, decrypts and reads the open password field of each metadata in the access control metadata structure table using the AES-256 algorithm, and reads the function control fields respectively. The offline reader controls the use of the offline copy file based on the content of the control fields.

6. A method for utilizing offline electronic archive files based on PDF security mechanisms, characterized in that, The document management system verifies the identity of the offline document reader and sets access control permissions based on the received application for offline document access, generates an offline copy of the electronic document, and writes the access control permissions for offline access of the electronic document into the offline copy file; Once approved, the offline document reader acquires an offline copy file, reads the access control metadata structure table of the offline copy file, obtains the access control permissions for that offline copy file, and controls the use of the offline copy file based on the access control permissions. Document access control items include: offline copy file opening password, number of openings, opening time limit, copy control, save as control, print control, and hardware binding. Each time the offline document reader opens an offline copy file, it reads the access control metadata, reads the access control metadata object at the end of the file, decrypts the metadata value using a key, obtains the offline document reader's unique identifier and access control list, acquires operation control permissions, calculates the number of openings, and then encrypts and updates the access control metadata object.

7. The method according to claim 6, characterized in that, The process of generating an offline copy of an electronic archive includes: the archive management system generating a PDF document from the electronic archive file that has been approved for use, setting offline access permissions and generating watermark information, and writing the watermark information and access control permissions into the PDF copy file; writing access control permissions into the PDF copy file includes: encrypting the access control metadata table, writing it as an object at the end of the PDF archive file, adding a file access control metadata object that records document access control items at the end of the PDF document, and generating the archive copy file.

8. The method according to claim 7, characterized in that, The step of writing the object to the end of the PDF archive file includes: encrypting the access control metadata in the access control metadata table to obtain a series of ciphertext values ​​( , ... The obtained ciphertext value and the offline reader's special identifier are combined into extended data. The extended data and the end of the electronic document PDF file are merged to obtain merge information. The hash value of the merge information is calculated, and the hash value is digitally signed. The hash value of the digital signature is placed before the end identifier of the PDF document.

9. The method according to any one of claims 6-8, characterized in that, The offline reader opens a PDF copy file, reads the access control object metadata of the PDF file, accesses the access control metadata structure table using a key, decrypts and reads the open password field of each metadata in the access control metadata structure table using the AES-256 algorithm, and reads the function control fields respectively. The offline reader controls the use of the offline copy file based on the content of the control fields.

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