Boxcryptor Single File Decryptor

This project provides a command-line utility for decrypting Boxcryptor-encrypted files. It's built with .NET 8.0 and requires the Microsoft.AspNetCore.Cryptography.KeyDerivation package.

Requirements

• .NET 8.0 SDK or runtime
• Microsoft.AspNetCore.Cryptography.KeyDerivation NuGet package (automatically restored when building)

Building the Project

Using build scripts

The project includes convenient build scripts for both Linux/macOS and Windows:

Linux/macOS:

./build.sh

Windows:

build.bat

These scripts will build the project, run tests, and optionally create standalone executables for multiple platforms.

Manual build

To build the project manually, use the .NET CLI:

dotnet build

Creating standalone executables

To create standalone executables that don't require .NET to be installed:

dotnet publish BCFileDecryptor/BCFileDecryptor.csproj -c Release -r win-x64 --self-contained true -p:PublishSingleFile=true -o publish/win-x64

Replace win-x64 with linux-x64 or osx-x64 for other platforms.

Usage

BCFileDecryptor [path to .bckey file] [path to encrypted file] [pwd] [path for output (optional)]

Where:

• [path to .bckey file] is the path to your Boxcryptor key file
• [path to encrypted file] is the path to the encrypted file you want to decrypt
• [pwd] is your Boxcryptor password
• [path for output (optional)] is the output path for the decrypted file (if not provided, it will be derived from the encrypted file name)

Testing

The project includes a comprehensive test suite built with xUnit. The tests cover all the helper classes used in the decryption process:

• Base64Helper: Tests for Base64 encoding and decoding operations
• HashHelper: Tests for the SHA256 HMAC hash computation
• AESHelper: Tests for AES decryption functionality
• PBKDF2Helper: Tests for key derivation using PBKDF2
• RSAHelper: Tests for RSA decryption
• IntegrationTests: Tests for the overall workflow (with skipped tests that require real files)

To run the tests, use the .NET CLI:

dotnet test

Project Structure

• BCFileDecryptor: The main application containing the decryption logic

  • BCFileDecryptor.cs: Main entry point and decryption workflow
  • AccountData.cs: Handles parsing of the .bckey file
  • AESHelper.cs: Provides AES encryption/decryption functions
  • Base64Helper.cs: Handles Base64 encoding/decoding
  • FileData.cs: Parses encrypted file headers
  • HashHelper.cs: Computes SHA256 HMAC hashes
  • PBKDF2Helper.cs: Implements PBKDF2 key derivation
  • RSAHelper.cs: Handles RSA decryption

• BCFileDecryptorTests: Unit tests for the application

  • Base64HelperTests.cs: Tests for Base64 encoding/decoding (5 tests)
  • HashHelperTests.cs: Tests for HMAC functionality (5 tests)
  • AESHelperTests.cs: Tests for AES encryption/decryption (5 tests)
  • PBKDF2HelperTests.cs: Tests for key derivation (6 tests)
  • RSAHelperTests.cs: Tests for RSA decryption (3 tests)
  • IntegrationTests.cs: Tests for the overall workflow (3 tests, currently skipped)

Test Coverage

The test suite includes 28 tests in total, covering:

• 25 passing unit tests for the helper classes
• 3 integration tests (currently skipped as they require real Boxcryptor files)

These tests ensure:

• Correct Base64 encoding and decoding
• Proper HMAC hash generation and verification
• Accurate AES decryption with various parameters
• Correct PBKDF2 key derivation
• Proper handling of RSA decryption
• Error handling for invalid inputs

Continuous Integration/Deployment

This project uses GitHub Actions with separate workflows for CI and CD, each with multiple jobs:

CI Workflow (.NET CI)

The CI workflow has two jobs that run sequentially:

1. Build Job

   • Automatically runs on each push and pull request
   • Builds the project using .NET 8.0
   • Uploads build artifacts for the test job

2. Test Job

   • Runs after the build job completes successfully
   • Downloads the build artifacts
   • Runs all unit tests
   • Ensures code quality across platforms

CD Workflow (.NET CD - Release)

The CD workflow also has two jobs that run sequentially:

1. Build Release Job

   • Triggered manually or when a new release is created on GitHub
   • Builds the project using .NET 8.0
   • Generates standalone executables for Windows, Linux, and macOS
   • Uploads build outputs for the packaging job

2. Package Job

   • Runs after the build release job completes
   • Downloads the build outputs
   • Creates zip archives of the builds
   • Uploads build artifacts for easy downloading
   • Attaches the binaries to GitHub releases (when triggered by a release)

This separation allows for:

• Fast feedback on code changes via the CI pipeline
• Better parallelization and resource utilization
• Clear separation of concerns between building and testing/packaging
• Controlled releases via the manual CD pipeline
• Clean, versioned releases with properly packaged artifacts

Notes

• This tool only supports decryption of files encrypted with Boxcryptor.
• The application currently supports the bc01 file version.
• The decryption process requires the correct .bckey file and password for the encrypted files.
• The project has been updated from .NET Core 3.1 to .NET 8.0.
• Cross-platform builds are available through the CI/CD pipeline.