System and method for utilizing off-line electronic archive file based on PDF (Portable Document Format) security mechanism

Abstract

The invention discloses a method for utilizing an off-line electronic archive file based on a PDF security mechanism, which comprises the following steps: when an archive management system receives an archive off-line utilization application, the archive management system generates an off-line copy file of the electronic archive, approves and sets an access control authority; the method comprises the following steps: writing an electronic archive access control authority into a security mechanism of a PDF copy file, setting a utilization authority of an archive offline copy file, opening the offline copy file by a specified archive offline reader, querying an access control metadata object in an access control table, and according to the utilization authority in the metadata object, accessing the PDF copy file; and controlling the offline reader to use the electronic file to offline copy the file.

Description

Technical Field

[0001] The present invention relates to the field of electronic file and information security technology, and is a protection technology for offline use of electronic archives, and in particular to a protection method for offline use of electronic archives based on PDF security mechanism extension. Background Art

[0002] At present, in the process of offline sharing and utilization of electronic archives, electronic archives are usually generated as archive copy files in PDF format. Security behavior controls are added to the archive copy files (such as: opening password, whether printing is allowed, whether editing is allowed), and then downloaded or copied to the local device for subsequent use. Generally, only the problem of "who can view" is solved, but how to further restrict the viewing process and the behavior after viewing cannot be controlled. Whether the downloaded copy file can be viewed again after the utilization time expires, such as whether it should be destroyed regularly after viewing, etc. Therefore, there is a great risk of file leakage in the offline use of electronic archive files.

[0003] Publication number: CN 117609967, title: "An application of archive preview authority based on non-proliferation technology". A method for applying archive preview authority based on non-proliferation technology is provided, which uses digital encryption technology and non-proliferation watermark processing to achieve safe reading and use of archives. This method can limit the illegal use of archive information and greatly reduce the risk of document proliferation.

[0004] In summary, the offline use of electronic archive files urgently requires a method for secure access control of electronic files to effectively solve the problems of anti-leakage, anti-diffusion and anti-tampering in the offline use of electronic archives. Summary of the invention

[0005] In order to solve the above problems, the present invention provides a protection method for offline use of electronic archives based on the expansion of PDF security mechanism. By setting security policies for offline electronic archive files, the requirements for electronic archive access control are written into the security mechanism of PDF files, and then the operation of archive copy files is controlled by the archive offline reader, so as to achieve the prevention of leakage, diffusion and tampering of archive information.

[0006] Based on the first aspect of the present invention, a system for utilizing offline electronic archive files based on a PDF security mechanism is proposed. The archive management system reviews the identity identification of the archive offline reader and sets access control permissions based on the received archive offline utilization application, generates an electronic archive offline copy file, and writes the electronic archive offline utilization access control permissions into the offline copy file; the archive offline reader that passes the review obtains the offline copy file, reads the access control metadata structure table of the offline copy file, obtains the access control permissions of the offline copy file, and controls the utilization of the offline copy file based on the access control permissions.

[0007] Further preferably, the generation of offline copy files of electronic archives includes: the archive management system generates PDF format documents from the electronic archive files that are agreed to be used, sets offline use permissions and generates watermark information, and writes the watermark information and access control permissions into the PDF copy files.

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

[0009] Further preferably, the step of writing the object into the PDF archive file tail includes: encrypting the access control metadata in the access control metadata table to obtain a series of ciphertext values ​​(C1, C2...C n ), combine the obtained ciphertext value and the archive offline reader special identifier into extended data, merge the extended data and the end of the electronic archive PDF file to obtain the merged information, calculate the hash value of the merged information, digitally sign the hash value, and put the digitally signed hash value before the end identifier of the PDF archive file.

[0010] Further preferably, the document access control items include: offline copy file opening password, opening times, opening time limit, copy control, save control, print control, and hardware binding. The archive offline reader reads the access control metadata each time it opens the offline copy file, reads the access control metadata object at the end of the file, decrypts the metadata value using the key, obtains the archive offline reader's special identifier and access control list, obtains the operation control authority, calculates the opening times, and then encrypts and updates it to the access control metadata object.

[0011] Further preferably, the offline reader opens the PDF copy file, reads the access control object metadata of the PDF file, uses the key to access the access control metadata structure table, uses the AES-256 algorithm to decrypt and read the opening password field of each metadata in the access control metadata structure table, reads the function control field respectively, and the offline reader controls the use of the offline copy file according to the content of the control field.

[0012] Based on the second aspect of the present application, a method for utilizing offline electronic archive files based on a PDF security mechanism is proposed, including: the archive management system reviews the identity identification of the archive offline reader and sets access control permissions based on the received archive offline utilization application, generates an electronic archive offline copy file, and writes the electronic archive offline utilization access control permissions into the offline copy file; the archive offline reader that has passed the review obtains the offline copy file, reads the access control metadata structure table of the offline copy file, obtains the access control permissions of the offline copy file, and controls the utilization of the offline copy file according to the access control permissions.

[0013] Further preferably, the generation of an offline copy file of an electronic archive includes: the archive management system generates a PDF format document from the electronic archive file that is agreed to be used, sets offline use permissions and generates watermark information, and writes the watermark information and access control permissions into the PDF copy file; the writing of access control permissions into the PDF copy file includes: encrypting the access control metadata table, writing it into the end of the PDF archive file as an object, adding a file access control metadata object that records document access control items at the end of the PDF document, and generating an archive copy file.

[0014] Further preferably, the step of writing the object into the PDF archive file tail includes: encrypting the access control metadata in the access control metadata table to obtain a series of ciphertext values ​​(C1, C2...C n ), combine the obtained ciphertext value and the archive offline reader special identifier into extended data, merge the extended data and the end of the electronic archive PDF file to obtain the merged information, calculate the hash value of the merged information, digitally sign the hash value, and put the digitally signed hash value before the end identifier of the PDF archive file.

[0015] Further preferably, the offline reader opens the PDF copy file, reads the access control object metadata of the PDF file, uses the key to access the access control metadata structure table, uses the AES-256 algorithm to decrypt and read the opening password field of each metadata in the access control metadata structure table, reads the function control field respectively, and the offline reader controls the use of the offline copy file according to the content of the control field.

[0016] The present invention effectively manages and constrains the archive file copies downloaded or copied to local devices for subsequent use by adding security behavior control to the archive copy files, writes the requirements of electronic archive access control into the security mechanism of PDF files by setting security policies for the files, and then controls the operation of the archive copy files by the archive offline reader to achieve the prevention of archive information leakage, diffusion and tampering. It not only solves the problem of "who can read", but also solves the problem of how to use it, manages and controls the reading objects, time, number of times, copying, printing, saving and other capabilities of offline electronic archive files, and solves the risks of file leakage and expansion of scope in the offline use of electronic archive files. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0018] Figure 2 A schematic diagram of generating a copy file for adding an access control metadata object in this exemplary embodiment;

[0019] Figure 3 Schematic diagram of the offline reader access control flow in this exemplary embodiment. DETAILED DESCRIPTION

[0020] The present invention provides a protection method for offline use of electronic archives based on the expansion of PDF security mechanism. By setting security policies for files, the requirements for electronic archive access control are written into the security mechanism of PDF files, and then the operation of archive copy files is controlled by an archive offline reader, so as to achieve the prevention of archive information leakage, diffusion and tampering.

[0021] like Figure 1 The schematic diagram of the overall business process of archive offline utilization in this exemplary embodiment is shown. The archive management system generates an offline copy file of an electronic archive in PDF format, writes an access control table of the electronic archive into the security mechanism of the PDF copy file, sets the utilization rights of the offline copy file of the archive, and when the archive management system receives an application for offline utilization of the archive, the specified offline reader of the archive opens the offline copy file, queries the access control metadata object in the access control table, and controls the offline reader to utilize the offline copy file of the electronic archive according to the utilization rights in the metadata object.

[0022] Application for offline use of archives. The archive user searches for the archives he needs to use based on the archive number and other information, fills in and submits the archive use application information, which includes the use method, use time, purpose and other information.

[0023] For example, if the user of the archives applies for the pre-job training plan and obtains the training courseware, the user submits the application, and the system searches for the storage location of the training plan and training courseware, the current status and usage of the archives, the usage rights, and whether approval is required.

[0024] Approval for offline use of archives. For archives that require approval, archive management personnel approve electronic archive use applications, review use information, and set use permissions and time limits for offline use of electronic archives. Specifically, corresponding file operation control permissions can be set for the use of offline electronic archive copies (such as setting open passwords, opening times, opening time limits, copy control, save control, print control, hardware binding, etc.).

[0025] For example, the permission settings for offline copies of archives include: setting the password for opening the offline copy of the archive, the number of times it can be opened, the validity period, the opening device (specified terminal or all terminals), whether to allow file printing, saving, save as, copying, screenshots, the name of the person using the offline archive, etc.

[0026] Archive copy file generation. The archive management system packages the electronic files involved in the electronic archives that have been reviewed and approved for use into a PDF format archive copy file. The copy file generation includes: generating watermark information based on the archive application applicant, the validity period of the copy, and the use rights, writing the watermark information into the PDF format file of the electronic archive to be used, and encrypting the various access control permission items set during approval and writing them into the PDF file. Encrypting the PDF file ensures that the file can only be parsed using the specified archive offline reader.

[0027] Specifically, a file access control metadata object is added at the end of the PDF document to record the document access control items. The document access control items are written into the access control metadata object. The document access control items include: PDF copy document opening password, opening times, opening time limit, copy control, save control, print control, hardware binding and other permissions. After the electronic archive offline reader reads the access control metadata each time a document is opened, the control metadata is decrypted using the key. At the same time, the access times are calculated and then encrypted and updated to the access control metadata object.

[0028] First, encrypt the access control metadata table and write it to the end of the PDF archive file as an object to generate an archive copy file. Encrypt the metadata in the access control metadata table to obtain a series of ciphertext values ​​(C1, C2...C n ), the obtained ciphertext value and the archive offline reader special identifier are combined into extended data, the extended data and the electronic archive PDF file tail are merged to obtain merged information, the hash value of the merged information is calculated, and the hash value is digitally signed.

[0029] Archive copy files and access control authority analysis. When an offline file is needed to be opened by an archive offline reader, the offline file PDF document structure is first analyzed, the access control metadata object at the end of the file is read, the metadata value is decrypted using the key, and the archive offline reader special identifier and access control list are obtained to obtain the operation control authority.

[0030] Through the above method, when the electronic archive file needs to be downloaded for offline use, the digital signature information at the end of the archive PDF file is used to verify the security of the dedicated archive offline reader and its access control authority, thereby preventing unauthorized readers from obtaining the offline archive file and further controlling the operation and processing of the offline electronic archive file.

[0031] A timestamp can be added when signing to provide support for the subsequent use of electronic archive files to authenticate the signature time. The signature value can be placed between the merged information and the tail identifier of the offline electronic file.

[0032] The access count is updated in real time, and encryption and signing are used to ensure that the file access control metadata object itself cannot be tampered with.

[0033] Design access control metadata objects, embed them into the metadata of PDF documents, and associate them with PDF copy documents using a unique identifier. Metadata objects include: opening password, number of allowed openings, number of openings, validity period, copy control, print control, save control, etc.

[0034] like Figure 2 The figure shows a schematic diagram of adding access control metadata objects to generate a copy file.

[0035] Archive copy file generation. Encrypt the access control metadata structure table and put it into 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 into the electronic archive PDF copy file as an object, and generate an 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 Number of opens allowed 3 3 Number of times opened 1 4 Document validity period 2024 / 2 / 1 / 23:59 5 Copy Control Allow / Disallow 6 Save Control Allow / Disallow 7 Save Control Allow / Disallow 8 Print Control Allow / Disallow 9 Screenshot Control Allow / Disallow 10 Device Control Bse72u 11 CPU serial number Bse72u

[0039] Encryption protection and digital signature can be used to encrypt access control metadata. An access password can be set for the access control to metadata structure table to ensure that the access control metadata can only be decrypted by a dedicated archive reader. The access control metadata can be signed with a digital signature.

[0040] Encryption protection: AES-256 encryption algorithm can be used to encrypt access control metadata data or source data tables to ensure that the metadata value can only be decrypted and modified by the archive offline reader.

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

[0042] Download the archive copy file. After the archive use application is approved, the archive management system checks the operating system (Windows, Linux, Android) of the archive user's device, selects the format corresponding to the operating system, and downloads the approved archive copy file together with the PDF archive offline reader to the archive user's device.

[0043] Archive offline reader detection. When the archive copy file is opened, the archive management system verifies whether the key detection is for archive offline reader access. If it is for archive offline reader access, it agrees to open the access control metadata structure table and read the access control metadata therein, and agrees to open the archive copy file. If it is not for archive offline reader access, the archive management system refuses to access the archive copy file and prompts "Please download the dedicated archive offline reader".

[0044] like Figure 3 The access control implementation process in this exemplary embodiment is shown, including: the offline reader opens the archive copy PDF file, performs file structure analysis, determines whether the offline reader used to open the file is a dedicated reader of the archive copy according to the key, if so, the dedicated reader analyzes the file structure, reads the "access control" object metadata of the PDF file, reads the open password field of the object metadata, detects and compares the open password with the password entered by the user, passes user identity authentication, reads the allowed opening times field, reads the opened times field, compares it with the allowed opening times in the object metadata, if it is less than the allowed opening times, reads the archive copy document validity period control field, reads the system current time, compares whether the current time is greater than the validity period, if it is less than the validity period, 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 the printing; reads the save control field, if the save control field is prohibited, the offline reader controls the archive copy to be saved; reads the save control field, if the save control field is prohibited, the offline reader controls the save. When it is greater than the allowed opening times or greater than the valid opening period of the copy file, the offline reader is prohibited from opening the archive copy file.

[0045] Control measures include:

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

[0047] (2) Opening times control: The archive offline reader reads the "allowed opening times" and "opening times" fields in the metadata object of the file access control, obtains the corresponding field values, and compares them with the opening times and opening times of the copy file. If the opening times are greater than the allowed opening times, the archive management system sends a reminder that "the archive has exceeded the allowed access times and is not allowed to be accessed". When the opening times are greater than the allowed opening times, the offline reader parses and displays the content of the file according to the PDF parsing standard, and at the same time, adds 1 to the opening times and encrypts it using the AES-256 encryption algorithm and writes it back to the "opening times" field in the metadata object.

[0048] (2) Validity period control: When an offline reader opens an archive copy file, it first accesses the time server on the Internet to obtain the current operation time. If the Internet cannot be accessed, it obtains the operating system time as the current time; it extracts the "document validity period" field in the metadata object of the file access control, reads the corresponding field value and compares it with the current time. If the current time is greater than the document validity period, a reminder "The archive has exceeded the validity period and access is not allowed" is sent. If the current time is less than the document validity period, the offline reader parses and displays the file content according to the PDF parsing standard.

[0049] (3) Copy control: Read the "Copy Control" field in the metadata object of the access control. If the field value is prohibited, the offline reader issues a disable command to disable the operating system's "Ctrl+C" and copy key copy functions, and also disables the "Copy" function button of the right mouse button, thereby limiting the copying of file contents and preventing leakage and spread.

[0050] (4) Save Control: Read the "Save Control" field in the metadata object of the access control. If the field value is prohibited, the save button of the file is 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 the access control. If the field value is prohibited, the Save As button of the file is disabled to prevent the user from saving as another file.

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

[0053] (6) Open device: Read the "Open device" field in the metadata object of access control. If the field value is not empty, it is required to open in the specified settings. Read the CPU serial number of the current computer through the offline reader. If the field value is consistent with the CPU serial number of the specified device, the device is allowed to open the archive file copy; compare it with the "CPU serial number" field value in the metadata object. If the field value is inconsistent with the CPU serial number of the current computer, remind the user that "the archive is not allowed to be accessed outside the specified computer". If they are consistent, the file content is displayed.

[0054] (8) Screenshot control: Read the "Screenshot control" field in the metadata object of the access control. If the field value is prohibited, the archive offline reader monitors the keyboard and mouse events of the operating system. When the mouse moves out of the reader's file content display area or triggers a keyboard key, the file display content is masked using a mask page. After masking, the mouse moves back to the mask page and clicks it to hide the mask page again and display the file content again to prevent leakage and spread.

Claims

1. A system for utilizing offline electronic archive files based on PDF security mechanism, characterized in that: The archive management system reviews the identity of the archive offline reader and sets access control permissions based on the received archive offline use application, generates an offline copy file of the electronic archive, and writes the access control permissions for offline use of the electronic archive into the offline copy file; The approved archive offline reader obtains the offline copy file, reads the access control metadata structure table of the offline copy file, obtains the access control authority of the offline copy file, and controls the use of the offline copy file according to the access control authority.

2. The system according to claim 1, characterized in that The generation of offline copy files of electronic archives includes: the archive management system generates PDF format documents from the electronic archive files that are approved for use, sets offline use permissions and generates watermark information, and writes the watermark information and access control permissions into the PDF copy files.

3. The system according to claim 2, characterized in that The writing of access control permissions into the PDF copy file includes: encrypting the access control metadata table, writing it into the end of the PDF archive file as an object, adding a file access control metadata object recording document access control items at 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 PDF archive file tail as an object comprises: encrypting the access control metadata in the access control metadata table to obtain a series of ciphertext values ​​(C1, C2...C n ), combine the obtained ciphertext value and the archive offline reader special identifier into extended data, merge the extended data and the end of the electronic archive PDF file to obtain the merged information, calculate the hash value of the merged information, digitally sign the hash value, and put the digitally signed hash value before the end identifier of the PDF archive file.

5. The system according to claims 1-4, characterized in that: Document access control items include: offline copy file opening password, opening times, opening time limit, copy control, save control, print control, and hardware binding. The archive offline reader reads the access control metadata each time it opens an offline copy file, reads the access control metadata object at the end of the file, decrypts the metadata value using the key, obtains the archive offline reader's special identifier and access control list, obtains operation control permissions, calculates the opening times, and then encrypts and updates it to the access control metadata object.

6. The system according to claims 1-4, characterized in that: The offline reader opens the PDF copy file, reads the access control object metadata of the PDF file, uses the key to access the access control metadata structure table, uses the AES-256 algorithm to decrypt and read the opening password field of each metadata in the access control metadata structure table, and reads the function control field respectively. The offline reader controls the use of the offline copy file according to the content of the control field.

7. A method for utilizing offline electronic archive files based on PDF security mechanism, characterized in that: The archive management system reviews the identity of the archive offline reader and sets access control permissions based on the received archive offline use application, generates an offline copy file of the electronic archive, and writes the access control permissions for offline use of the electronic archive into the offline copy file; The approved archive offline reader obtains the offline copy file, reads the access control metadata structure table of the offline copy file, obtains the access control authority of the offline copy file, and controls the use of the offline copy file according to the access control authority.

8. The method according to claim 7, characterized in that The generation of an offline copy file of an electronic archive includes: the archive management system generates a PDF format document from the electronic archive file that is agreed to be used, sets offline use permissions and generates watermark information, and writes the watermark information and access control permissions into the PDF copy file; the writing of access control permissions into the PDF copy file includes: encrypting the access control metadata table, writing it into the end of the PDF archive file as an object, adding a file access control metadata object that records document access control items at the end of the PDF document, and generating an archive copy file.

9. The method according to claim 8, characterized in that The step of writing the PDF archive file tail as an object comprises: encrypting the access control metadata in the access control metadata table to obtain a series of ciphertext values ​​(C1, C2...C n ), combine the obtained ciphertext value and the archive offline reader special identifier into extended data, merge the extended data and the end of the electronic archive PDF file to obtain the merged information, calculate the hash value of the merged information, digitally sign the hash value, and put the digitally signed hash value before the end identifier of the PDF archive file.

10. The method according to any one of claims 7 to 9, characterized in that: The offline reader opens the PDF copy file, reads the access control object metadata of the PDF file, uses the key to access the access control metadata structure table, uses the AES-256 algorithm to decrypt and read the opening password field of each metadata in the access control metadata structure table, and reads the function control field respectively. The offline reader controls the use of the offline copy file according to the content of the control field.

Images