Ceaser Cypher

This project implements Caesar Cipher encryption and decryption in Assembly language using the Irvine32 library. The program allows users to input a text file and a shift key, then either encrypts or decrypts the text based on the user's choice.

Group Members

• Radeel Ahmed
• Muhammad Abdullah

Project Structure

• Irvine32.inc and macros.inc are included for basic I/O operations.
• BUFFER_SIZE is set to 100 bytes to handle input data.
• data section contains necessary variables and prompts for user input.
• code section contains the main procedure and encryption/decryption logic.

How to Run the Program

• Compile and Link: Use an assembler like MASM to compile and link the program.

ml /c /coff yourfilename.asm
link /subsystem:console yourfilename.obj Irvine32.lib

• Execute the Program: Run the compiled executable.

yourfilename.exe

• Input Filename: Enter the name of the input file containing the plaintext or ciphertext.

• Select Choice: Enter 1 for encryption. Enter 2 for decryption.

• Enter Shift: Input the shift key (a numerical value) for the Caesar Cipher.

• View Results: The program will display the ciphertext if you selected encryption or the plaintext if you selected decryption.

Detailed Description

Main Procedure

• Displays the project title and group member names.
• Prompts the user for the input filename.
• Opens the specified file and reads its contents into a buffer.
• Asks the user to choose between encryption and decryption.
• Prompts the user to enter a shift key for the Caesar Cipher.

Encryption

• Iterates over each character in the buffer.
• Checks if the character is uppercase or lowercase.
• Applies the Caesar Cipher shift to each letter.
• Stores the encrypted characters in an array.
• Displays the resulting ciphertext.

Decryption

• Iterates over each character in the buffer.
• Checks if the character is uppercase or lowercase.
• Applies the reverse Caesar Cipher shift to each letter.
• Stores the decrypted characters in an array.
• Displays the resulting plaintext.

Example

***********************
Project Caesar Cipher
***********************

---------------------------------------------------
Group Members
Radeel Ahmad - 221544
Muhammad Abdullah - 221546
-----------------------------------------------------

Enter an input filename: input.txt
Select Choice
1. For encryption
2. For decryption
Enter shift: 3

Plaintext is: HELLO
Ciphertext is: KHOOR

Notes

• Ensure the input file exists in the same directory as the executable.
• The shift key should be a positive integer.
• The program only processes alphabetic characters; other characters are left unchanged.