README.md

ElGamal Public-Key Encryption Implementation

Overview

This project implements the ElGamal Public-Key Encryption scheme in C++ using the BigInt library for working with large integers. The program allows users to generate public and private keys, encrypt plaintext messages, and decrypt ciphertext messages.

Implementation Details

• Language: C++11 or older
• BigInt

Files and Folders Included

• BigInt: Contains the BigInt header file
  • bigint.h: BigInt header file also containing inline implementations
• ElGamal: Containts the ElGamal header file and implementation file
  • elgamal.h: Contains header for libraries included, functions, and public key variables
  • elgamal.cpp: Implementation file containing implementation of all ElGamal functions
• main.cpp: Main file implementating the console interface for encryting and decryting messages

How to run with VSCode

1. Open the main.cpp directory.
2. Build and Run
3. If there is error linking the files
   1. Open the tasks.json file in your Visual Studio Code workspace (.vscode directory)
   2. Ensure that the args property within the "tasks" array looks like the following:

          "args": [
              "-fdiagnostics-color=always",
              "-g",
              "main.cpp",               // Compile main.cpp
              "ElGamal/elgamal.cpp",    // Compile ElGamal/elgamal.cpp
              "-I",
              "BigInt",                 // Include BigInt folder
              "-o",
              "${fileDirname}\\${fileBasenameNoExtension}.exe"
          ],

   3. Save the tasks.json file.
   4. Build and Run in main.cpp

How to run with command line

1. Build: g++ -o output.exe main.cpp ElGamal/elgamal.cpp -I BigInt -std=c++11
2. Run: ./main.exe

Interacting with the Program

• Follow the on-screen instructions provided by the program:
  • Encryption
    • Type 'E' to encrypt a message
    • Enter message for encrytion
    • Enter desire key size(must be larger than message)
      • [!WARNING] encryption will take longer with large messages and key size
    • You be provided with the public key, secret private key, and cipher text γ and δ
  • Decryption (must first encrypt a message while program is running to decrypt)
    • Provide γ and δ and private key
    • You will be provided the original message.