Visual Cryptography Implementation

Overview

This project implements Visual Cryptography, a cryptographic technique that allows visual information (images, text, etc.) to be encrypted in a way that the decryption can be performed by the human visual system, without the aid of computers.

What is Visual Cryptography?

Visual Cryptography is a method of encrypting a visual information (picture, text, etc.) in such a way that:

• The original information is divided into two or more pieces (shares)
• Each individual share reveals no information about the original image
• When the shares are properly aligned and overlaid, the original information becomes visible

Basic Principle

For a binary image (black and white):

• Each pixel is divided into 2×2 sub-pixels

• For a white pixel: Share 1: [1 0] Share 2: [1 0] Overlay: [1 0] = White pixel [0 1] [0 1] [0 1]

• For a black pixel: Share 1: [1 0] Share 2: [0 1] Overlay: [0 0] = Black pixel [0 1] [1 0] [0 0]

Features

• Converts input images to binary (black and white) format
• Generates two complementary shares
• Supports image overlay to reveal the secret
• Handles various image sizes with automatic scaling
• Includes error handling and memory management
• Provides visual feedback through OpenCV windows

Requirements

• Visual Studio 2019/2022
• OpenCV 4.12.0
• C++17 or later
• Windows OS (for current implementation)

Installation & Setup

1. Install OpenCV

1. Download OpenCV 4.12.0 from the official website
2. Extract to C:\opencv
3. Add OpenCV bin directory to system PATH: C:\opencv\build\x64\vc16\bin

2. Project Setup in Visual Studio

1. Create new Empty C++ Project
2. Set platform to x64
3. Configure project properties:

a. Include Directories: C:\opencv\build\include

b. Library Directories: C:\opencv\build\x64\vc16\lib

c. Additional Dependencies: opencv_world4120d.lib (Debug) opencv_world4120.lib (Release)

3. DLL Setup

Copy from C:\opencv\build\x64\vc16\bin:

• For Debug: opencv_world4120d.dll
• For Release: opencv_world4120.dll

To your project's output directory: YourProject\x64\Debug YourProject\x64\Release\

Usage

Basic Usage

// Create or load an image cv::Mat inputImage = cv::imread("input.png", cv::IMREAD_GRAYSCALE);

// Initialize Visual Cryptography VisualCryptography vc(inputImage);

// Generate shares auto shares = vc.generateShares(); cv::Mat share1 = shares.first; cv::Mat share2 = shares.second;

// Create overlay (decrypt) cv::Mat result = vc.overlayShares(share1, share2); Running the Demo Build the project in Visual Studio Run the executable

The program will:

Create a test image Generate two shares Save shares as PNG files Display all images in windows Create and show the overlay result Technical Details Implementation Logic

Image Processing:

• Convert input to binary (black/white) format
• Scale image if needed
• Process image in memory-efficient chunks

Share Generation:

• Each pixel is expanded to 2×2 sub-pixels
• Random pattern selection for white pixels
• Complementary patterns for black pixels
• Shares are stored as separate images

Overlay Process:

• Bitwise AND operation between shares
• Processed in chunks for memory efficiency
• Results in visible secret image

Memory Management

• Automatic image scaling for large inputs
• Chunk-based processing for memory efficiency
• Proper cleanup of OpenCV resources

Limitations

• Works with binary (black and white) images only
• Output images are 2x larger than input
• Some loss of resolution due to pixel expansion

Contributing

Feel free to fork this repository and submit pull requests. For major changes, please open an issue first to discuss what you would like to change.

License

MIT License

Acknowledgments

• OpenCV team for the computer vision library
• Visual Cryptography concept by Moni Naor and Adi Shamir (1994)