Encryption-Decryption MASM615

A comprehensive encryption and decryption program developed entirely in Assembly Language using XOR bitwise operations. This project demonstrates secure data handling, file I/O operations, and low-level programming concepts in a user-friendly console interface.

Table of Contents

• Overview
• Features
• Technical Specifications
• Program Functionality
• Installation & Setup
• Usage Guide
• File Structure
• Technical Implementation
• Deployment
• Troubleshooting
• Contributing
• License
• Author
• Acknowledgments

Overview

The Encryption-Decryption project is a semester project that showcases the power of Assembly Language in implementing cryptographic operations. Built using MASM615, this program provides a complete solution for encrypting text data using XOR operations and storing it securely in files.

Key Highlights

• Pure Assembly Language Implementation: Demonstrates low-level programming expertise
• XOR Encryption Algorithm: Simple yet effective symmetric encryption
• File-based Data Persistence: Secure storage and retrieval of encrypted data
• Interactive Menu System: User-friendly console interface
• Educational Value: Perfect for understanding encryption concepts and Assembly programming

Features

• 🔐 Data Encryption: Encrypt text strings using XOR bitwise operations
• 🔓 Data Decryption: Decrypt and view original data seamlessly
• 💾 File Operations: Store encrypted data in files (MICHU.txt)
• 👁️ Data Visualization: Display encrypted data in its raw form
• 🗑️ Data Management: Delete stored encrypted data
• 📋 Menu-Driven Interface: Easy-to-use console navigation
• ⚡ Fast Processing: Optimized Assembly code for efficient execution
• 🔄 Session Management: Continue operations until user exits

Technical Specifications

Specification	Details
Language	Assembly Language (MASM615)
Architecture	x86 (16-bit)
Memory Model	Small Model
Stack Size	100h bytes
Encryption Method	XOR Bitwise Operation
File Format	Plain text (.txt)
Platform	DOSBox recommended
Assembler	MASM615

Program Functionality

The program offers five main operations through an interactive menu:

Menu Options

----------------------------------
1-ADD Data in Encrypted file
2-Read decrypted data
3-show Data from Encrypted file
4-Delete Data from Encrypted file
5-Exit Program
----------------------------------

Detailed Operation Descriptions

1. ADD Data in Encrypted File

• Prompts user to enter a string
• Applies XOR encryption (key: 1)
• Stores encrypted data in MICHU.txt
• Confirms successful encryption

2. Read Decrypted Data

• Reads encrypted data from file
• Applies XOR decryption to restore original text
• Displays the decrypted string on screen

3. Show Data from Encrypted File

• Reads and displays raw encrypted data
• Shows the actual encrypted bytes stored in file
• Useful for understanding encryption results

4. Delete Data from Encrypted File

• Allows user to specify file for deletion
• Creates user-defined files for data management
• Provides file creation confirmation

5. Exit Program

• Safely terminates the application
• Cleans up resources and memory

Installation & Setup

Prerequisites

1. DOSBox Emulator

   • Download from dosbox.com
   • Install and configure DOSBox on your system

2. MASM615 Assembler

   • Ensure MASM615 is available in your DOSBox environment
   • Set up proper PATH variables for MASM tools

Setup Instructions

1. Clone the Repository

   git clone https://github.com/chmuhammadasim/Encryption-Decryption-masm615.git
   cd Encryption-Decryption-masm615

2. Mount Directory in DOSBox

   mount c: /path/to/project/directory
   c:
   

3. Compile the Program

   masm asim.asm
   link asim.obj
   

4. Run the Executable

   asim.exe
   

Usage Guide

Starting the Program

1. Launch the compiled executable
2. The program displays a welcome screen with menu options
3. Enter your choice (1-5) when prompted

Example Workflow

1. Encrypt Data:

   • Select option 1
   • Enter your text string
   • Program encrypts and saves to file

2. View Encrypted Data:

   • Select option 3
   • View the raw encrypted content

3. Decrypt Data:

   • Select option 2
   • See your original text restored

4. Exit:

   • Select option 5 to terminate

Sample Session

Enter Option : 1
Enter String 1: Hello World
Your data has been encrypted!

Enter Option : 3
encrypted Data: Ifmmp!Xpsme

Enter Option : 2
decryption: Hello World

File Structure

Encryption-Decryption-masm615/
├── asim.asm          # Main assembly source code
├── asimlib.lib       # Assembly library file
├── README.md         # Project documentation
├── LICENSE          # MIT License file
├── MICHU.txt        # Generated encrypted data file (runtime)
└── .gitattributes   # Git configuration

File Descriptions

• asim.asm: Core implementation containing all procedures and program logic
• asimlib.lib: External library providing additional assembly functions
• MICHU.txt: Default output file for storing encrypted data (created at runtime)

Technical Implementation

Encryption Algorithm

The program uses a simple XOR cipher with key value 1:

encryption proc near
    mov dx,offset mybuf1
    mov ah, 3Fh
    int 21h
    mov cx,lengthof mybuf1
    mov bx,0
    l1:
    xor mybuf1[bx],1    ; XOR each byte with 1
    inc bx
    loop l1
    ret
encryption endp

Key Components

1. Data Structures:

   • Menu strings for user interface
   • Input/output buffers (100 bytes)
   • File handle management
   • User choice storage

2. File Operations:

   • File creation and opening
   • Reading and writing encrypted data
   • Proper file handle management

3. Memory Management:

   • Register clearing procedures
   • Stack and data segment setup
   • Buffer management

Security Considerations

• XOR with key 1: Simple encryption suitable for educational purposes
• File-based storage: Data persists between program sessions
• Memory clearing: Registers are cleared after operations

Deployment

Production Environment

For optimal deployment and execution:

1. Recommended Platform: DOSBox v0.74 or higher
2. Assembler: MASM615 (Microsoft Macro Assembler)
3. Memory Requirements: Minimal (16-bit addressing)
4. Storage: Small footprint (~10KB for source files)

Compilation Steps

# Step 1: Assemble source code
masm asim.asm;

# Step 2: Link object file
link asim.obj;

# Step 3: Run executable
asim.exe

Distribution

The compiled executable (asim.exe) can be distributed independently with DOSBox for cross-platform compatibility.

Troubleshooting

Common Issues

1. "File not found" error

   • Ensure asimlib.lib is in the same directory
   • Check file permissions

2. Compilation errors

   • Verify MASM615 is properly installed
   • Check syntax and include paths

3. Runtime crashes

   • Ensure sufficient memory in DOSBox
   • Check stack size configuration

4. File access issues

   • Verify write permissions in directory
   • Check if MICHU.txt is locked by another process

Debug Tips

• Use DOSBox's debug mode for step-by-step execution
• Check register values during encryption/decryption
• Verify file contents with hex editor

Contributing

Contributions are welcome! Here's how you can help:

How to Contribute

1. Fork the Repository
2. Create a Feature Branch

   git checkout -b feature/amazing-feature

3. Make Your Changes
   • Follow assembly coding conventions
   • Add comments for complex operations
   • Test thoroughly in DOSBox
4. Commit Your Changes

   git commit -m 'Add amazing feature'

5. Push to Branch

   git push origin feature/amazing-feature

6. Open a Pull Request

Contribution Guidelines

• Maintain code readability and documentation
• Test all changes in DOSBox environment
• Follow existing code style and structure
• Update README if adding new features

Badges

License

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

Author

Muhammad Asim Chattha

• GitHub: @chmuhammadasim
• Institution: Air University, Islamabad, Pakistan
• Field: Computer Science Student

🚀 About Me

Hello, I'm Muhammad Asim Chattha, a dedicated Computer Science student currently pursuing my studies at Air University in Islamabad, Pakistan. This Encryption-Decryption project represents my semester work, showcasing expertise in Assembly Language programming and cryptographic concepts.

This project is not just a coding exercise but a journey into the realm of secure data handling through the ingenious use of XOR bitwise operations, demonstrating the power and precision of low-level programming.

Acknowledgments

• Air University - For providing the educational foundation
• Assembly Language Community - For continuous learning resources
• DOSBox Development Team - For maintaining compatibility
• Open Source Community - For inspiration and collaboration opportunities

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Feel free to explore, contribute, and delve into the fascinating world of assembly language and encryption! ⚡🔐