Table of Content
Offline Office files (locally stored Word, Excel, and PowerPoint documents) often contain a company’s core secrets—such as undisclosed financial reports, product formulas, and project blueprints. Once these files are removed from cloud-based controls, they become highly vulnerable to leakage via USB drives, email forwards, or screenshots. Traditional password protection only restricts access to open the file; once authorized users view the document, they can still content through printing, copy-paste, saving as PDF, or other means, leaving security ineffective.
bestCoffer has developed a dual “encryption + behavior control” technology solution to address the protection challenges of offline Office files. This article presents practical test results demonstrating its effectiveness in preventing printing and copying, offering insights for enterprises seeking to secure their core documents.
Test Environment and Methodology
Test Subjects
- Protected files: Confidential Word contracts (with text, tables, images), Excel financial models (with formulas and hidden sheets), and PowerPoint product plans (with sensitive diagrams).
- Protection tool: bestCoffer Enterprise Edition (V5.2.0), with the “Offline File Encryption” module enabled. Permissions were configured as “view-only; printing/copying/saving as prohibited.”
- Attack scenarios: Six common attempts by internal users to bypass protection were simulated: printing, copy-paste, screenshots, saving as alternative formats, format conversion, and file extension modification.
Core Technical Principles
bestCoffer employs a combined “application-layer encryption + driver-level control” approach:
- Office files are encrypted using the AES-256 algorithm, generating a protected proprietary format (.bcf) that can only be opened and decrypted via the bestCoffer client.
- When the file is opened, kernel-level drivers block system calls for printing, clipboard operations, and screen capture, fundamentally restricting content diffusion.
- Device fingerprinting (hardware ID + OS information) is bound to the file. Even if copied to another device, the file remains inaccessible without authorization.
Test Results for Six Attack Scenarios
Scenario 1: Anti-Printing Test
- Attempted operations: Opening the encrypted Word contract and attempting to print via “File > Print,” the Ctrl+P shortcut, or a virtual printer (e.g., Microsoft Print to PDF).
- Results: All printing options were grayed out, with a system message: “This file is protected and cannot be printed.” Reinstalling printers or using third-party print plugins did not bypass the restriction.
- Technical analysis: bestCoffer hooks into Office’s printing interfaces and system print services, blocking print commands for both physical and virtual printers, including third-party plugins.
Scenario 2: Anti-Copy-Paste Test
- Attempted operations:
- Selecting text/tables and using right-click “Copy” or Ctrl+C, then pasting into Notepad or a new document.
- Using the “Format Painter” to copy text styles (as an indirect method to extract content).
- Dragging selected content to other files.
- Results:
- Copy functions were disabled: the right-click “Copy” option was missing, and keyboard shortcuts had no effect.
- The Format Painter worked only within the protected document, not across files.
- Drag-and-drop operations failed to move content outside the document.
- Advantage over traditional methods: Basic password protection limits editing but not copying. bestCoffer directly blocks clipboard access, eliminating content extraction at the source.
Scenario 3: Anti-Screenshot Test
- Attempted operations:
- Using system screenshot tools (Win+Shift+S, Snipaste).
- Installing third-party screenshot software (e.g., FastStone Capture).
- Capturing the screen with a mobile phone camera.
- Results:
- System and third-party screenshot tools produced only blacked-out images for the protected document area.
- Mobile phone photos captured the content but revealed dynamic watermarks (with the user’s ID and device info), enabling leak (traceability).
- Security value: bestCoffer prevents digital screenshots and deters physical photography via watermarking, addressing the “loophole” of traditional encryption.
Scenario 4: Anti-Saving/Format Conversion Test
- Attempted operations:
- Using “Save As” to export the file as docx, pdf, or txt.
- Exporting via “Save as Web Page” to extract content.
- Converting the file using Office plugins (e.g., “Export to Image”).
- Results: All “Save As” options were disabled, and plugin-based conversions failed with the message: “Access to content is restricted.” No alternative formats could be generated.
Scenario 5: Anti-File Extension Modification Test
- Attempted operation: Renaming the encrypted .bcf file to .docx or .zip and attempting to open it with Office or compression software.
- Results: Modified files were unrecognizable by Office, and compression software reported “corrupted or invalid format.” No content could be extracted.
- (Principle): Encrypted files undergo structural reorganization (not just extension changes), ensuring only the bestCoffer client can parse them, resisting simple renaming attacks.
Scenario 6: Anti-Memory Extraction Test
- Attempted operation: Using memory-reading tools (e.g., Process Explorer) to extract plaintext content from the document while it was open.
- Results: Only encrypted data fragments were found in memory; no complete plaintext could be recovered.
- Security measure: A “memory encryption + real-time decryption” mechanism ensures content is only temporarily decrypted for on-screen rendering, with no full plaintext stored in memory, defending against advanced attacks.
Balancing Compatibility and User Experience
Encryption often comes at the cost of usability, but bestCoffer achieves a balance through thoughtful design:
- Granular permission control: Admins can configure “edit-allowed but copy-prohibited” access (e.g., enabling department managers to modify content while blocking leaks).
- Lightweight client: The 8MB installation package opens encrypted files almost as quickly as native Office (a 100-page Word document took <2 seconds to load in tests).
- Cross-version compatibility: Supports Office 2010–2021 and 365, as well as Windows 7/10/11, requiring no upgrades to existing enterprise software environments.
Feedback from a manufacturing enterprise test showed that after deploying bestCoffer, its R&D team’s offline product blueprints (Excel formulas + PowerPoint designs) remained secure during internal circulation, with no further leaks via copy-paste—all without sacrificing user workflow efficiency.
Conclusion: Core Advantages of Offline File Protection
Compared to traditional password protection or PDF encryption, bestCoffer’s offline Office protection technology offers three key benefits:
- Comprehensive protection coverage: Blocks all common leakage paths, from printing and copying to screenshots and format conversion, addressing the “security for honest users only” flaw of basic tools.
- Deep-layer security: Uses driver-level controls and memory encryption to resist technical bypass attempts, going beyond surface-level application restrictions.
- Usability-security balance: Maintains near-native Office performance while enforcing strict protection, reducing enterprise adoption barriers.
For enterprises needing to circulate core documents offline (e.g., R&D, finance, and legal departments), bestCoffer provides a “secure yet usable” solution, ensuring offline files no longer remain a weak link in data security.
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