AcornUnObfuscate

By Aidan Hutchinson, 06/02/2025

Acorn BBC BASIC Detokenizer and Deobfuscator

A Windows application for detokenizing and deobfuscating BBC BASIC source code files from Acorn/RISC OS systems. Features syntax highlighting similar to Visual Studio's style.

Features

• Detokenization: Converts tokenized BBC BASIC files (.bas) back into readable text
• Deobfuscation: Intelligently renames variables and procedures to make code more readable
• Syntax Highlighting: Visual Studio-style syntax highlighting for:
  • BBC BASIC keywords
  • String literals
  • Numbers (including hexadecimal)
  • Comments
  • Procedures and Functions
  • SYS calls
  • Operators

Installation

1. Download the latest release from the releases page
2. Extract the ZIP file to your desired location
3. Run AcornUnObfuscate.exe

Usage

Opening Files

1. Click File -> Open or press Ctrl+O
2. Select a BBC BASIC file (.bas extension or All Files to load ,bas file)
3. The detokenized source code will be displayed with syntax highlighting

Deobfuscating Code

1. Open a BBC BASIC file
2. Click Deobfuscate -> Deobfuscate to process the code
3. The deobfuscated version will appear with:
   • Meaningful variable names
   • Restructured procedure names
   • Preserved functionality
4. Use Deobfuscate -> Revert Changes to return to the original code

Supported File Formats

• BBC BASIC V tokenized files (.bas)
• Files from RISC OS and earlier Acorn systems

Technical Details

BBC BASIC File Format

The application handles the BBC BASIC V file format which includes:

• Line-based structure with line numbers
• Tokenized keywords
• Special handling for PROC/FN definitions
• SYS call formatting
• REM statement preservation

Deobfuscation Rules

Variables are renamed based on their:

• Usage context
• Data type (%, $, or no suffix)
• Scope (LOCAL or global)
• Relationship to procedures

Procedures are renamed based on their:

• Functionality
• System call patterns
• Usage context

Building from Source

Prerequisites

• Visual Studio 2022
• .NET 8

Build Steps

1. Clone the repository:

git clone https://github.com/aidanhutch/AcornUnObfuscate.git

2. Open AcornBasicDetokenizer.sln in Visual Studio

3. Build the solution:

   In Visual Studio press F5 or click green arrow to Build/Run app. Or in Visual Studio Code Terminal window type:

dotnet build

Contributing

1. Clone the repository
2. Create your feature branch (git checkout -b feature/amazing-feature)
3. Commit your changes (git commit -m 'Add some amazing feature')
4. Push to the branch (git push origin feature/amazing-feature)
5. Open a Pull Request
6. Contact me for review

License

This project is licensed under the MIT License - see the LICENSE file for details.

Acknowledgments

• Thanks to the Acorn/RISC OS community for documenting the BBC BASIC file format
• Built on research and documentation about the BBC BASIC tokenization system
• Inspired by the need for modern tools to work with classic Acorn software

Contact

Aidan Hutchinson - @aidanhutch

Release History

• 1.0.0
  • Initial release
  • Basic detokenization and syntax highlighting
• 1.1.0
  • Added deobfuscation feature
  • Improved syntax highlighting
• 1.2.0
  • Enhanced Visual Studio-style theme
  • Bug fixes for keyword highlighting