🕵️ LSB Image Steganography — C Project

Hide secrets in plain sight. A command-line tool written in C that invisibly embeds and extracts secret files inside 24-bit BMP images using the Least Significant Bit (LSB) technique — pixel-perfect and visually undetectable.

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🔍 How It Works

Each bit of your secret file is embedded into the Least Significant Bit of the image's pixel bytes. Since the human eye cannot detect a 1-bit change in color intensity, the stego image looks 100% identical to the original.

Original pixel byte:  1 1 0 1 0 1 1 [0]
Secret bit embedded:  1 1 0 1 0 1 1 [1]  ← Only LSB changes

• 🔐 A magic string #* is embedded during encoding and verified during decoding to authenticate stego images
• 🖼️ The output image retains the exact same dimensions, format, and visual quality
• ⚡ Works at the bit level — fast, lightweight, no external libraries needed

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✨ Features

Feature	Description
📥 Encode	Hide any file (.txt, .c, .sh, .h) inside a BMP image
📤 Decode	Extract hidden files from stego images
📏 Capacity Check	Validates image size before encoding to prevent overflow
🔑 Magic String Auth	#* marker ensures only valid stego images are decoded
🗂️ Multi-format Support	Supports multiple secret file types
🖼️ Lossless Quality	Original image dimensions and visual quality fully preserved

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🗂️ Project Structure

LSB-Steganography/
├── 📄 main.c          # Entry point — handles encode/decode routing
├── 📄 main.h          # Enums: OperationType, Status, uint
├── 📄 encode.c        # Full encoding logic
├── 📄 encode.h        # EncodeInfo struct and encoding function declarations
├── 📄 decode.c        # Full decoding logic
├── 📄 decode.h        # DecodeInfo struct and decoding function declarations
├── 📄 common.h        # Shared constants (magic string)
├── 📄 types.h         # User-defined types (Status, uint)
├── 🖼️ beautiful.bmp   # Sample source BMP image for testing
├── 🔒 secret.txt      # Sample secret file for encoding test
└── 📝 output.txt      # Output file after decoding

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🚀 Getting Started

🛠️ Prerequisites

• GCC compiler
• Linux / Unix environment

🔧 Build

# Clone the repository
git clone https://github.com/<your-username>/LSB-Steganography.git
cd LSB-Steganography

# Compile
gcc main.c encode.c decode.c -o stego

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📖 Usage

🔒 Encoding — Hide a secret file inside a BMP image

./stego -e <source.bmp> <secret_file> <output_stego.bmp>

Example:

./stego -e beautiful.bmp secret.txt stego.bmp

Output:

[INFO]    Mode: ENCODING
[INFO]    All input files validated. Starting encoding process...
[SUCCESS] Secret file has been encoded into the BMP image successfully!
          Output (stego image): stego.bmp

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🔓 Decoding — Extract a hidden file from a stego image

./stego -d <stego.bmp> <output_filename>

Example:

./stego -d stego.bmp output.txt

Output:

[INFO]    Mode: DECODING
[INFO]    Input stego image validated. Starting decoding process...
[SUCCESS] Secret file extraction complete!
          Output file: output.txt

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⚠️ Error Handling

❌ Error	💬 Message
Insufficient image capacity	Error: Image does not have sufficient capacity
Invalid BMP file	Error: Invalid argument for encoding/decoding
File not found	ERROR: Unable to open file
Wrong magic string	Error: Magic string mismatch

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🧠 Concepts Used

Concept	Role in Project
🔢 Bitwise Operations	Core LSB embedding and extraction logic
📁 File Handling	Reading BMP and secret files in binary mode
🖼️ BMP Image Format	Understanding pixel layout and header structure
🔏 LSB Technique	Hiding data in the least significant bits of pixel bytes
💻 Command-Line Arguments	Routing encode/decode operations via argc/argv
🧱 Structs	EncodeInfo and DecodeInfo for clean data management

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🛠️ Technologies Used

• Language: C
• Compiler: GCC
• Platform: Linux / Unix

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👤 Author

Amar C M 🔧 Embedded Systems Engineer

📧 amarcm1502@gmail.com

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📜 License

This project is open-source and available under the MIT License.

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💡 "The best hidden message is the one no one knows exists."