RSA Key Generator (C + GMP + OpenSSL)

Welcome to my first github project ! A custom RSA key pair generator written in C, using GMP/MPIR and OpenSSL. Now this might look like reinventing the wheel but the sole purpose of this project was for me to have an understanding and feel for combining encryption algorithms with C programming. This is just for learning purposes only and should not be used in production systems. By using this, you acknowledge that it may contain vulnerabilites and are doing it at your own risk.

Features

• Generate RSA public/private key pairs
• Configurable key sizes: 512, 1024, 2048, 3072, 4096 bits
• Outputs keys in standard PEM format (PKCS#1)
• Passphrase-protected private keys using AES-256-CBC
• Optimized with Chinese Remainder Theorem (CRT) parameters
• Compatible with OpenSSL tools
• Lightweight and fast (uses GMP/MPIR for big integer math)

Demo

$ ./build/rsa_program --outdir output
Enter key size (bits): 2048
[+] Generating 2048-bit RSA keypair...
[+] Exporting keys...
[+] RSA key validated successfully.
[+] Public key exported to output/public.pem
[+] Private key exported to output/private.pem
[+] RSA keypair generation complete. Keys are stored in 'output'.

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Installation & Build

Windows

• Make sure you're Windows 10/11 64-bit x86_64 arch
• Download and install MinGW-w64 and add the 'bin' folder to your system PATH
• Usually MinGW also installs GNU Make along with it, if not, download GNU Make For Windows
• Download Git for Windows and make sure to check installing Git Bash
• Clone and set up vcpkg

  git clone https://github.com/microsoft/vcpkg.git
  cd vcpkg
  .\bootstrap-vcpkg.bat

• Install the following dependencies using vcpkg

  vcpkg install mpir:x64-windows
  vcpkg install openssl:x64-windows
  vcpkg install gmp:x64-windows

• Integrate vcpkg globally

  vcpkg integrate install

• Clone the RSA repository

  git clone https://github.com/sidhantsharma24/RSA.git

Build the project

• Use Git Bash for this step

  make windows VCPKG_DIR=/c/Users/YourUsername/vcpkg/installed/x64-windows

Run the program

cd build
./rsa_program.exe

Linux (debian)

• GCC (Linux) or MinGW (Windows)
• GMP or MPIR library installed
• OpenSSL development libraries installed

You might need to build MPIR from source

• MPIR Library

Additional packages

sudo apt-get install libgmp-dev libssl-dev

Build project

make

Clean build files

make clean

Usage

./build/rsa_program --outdir output

Output

Keys will be exported in PEM format to the specified directory (or the default output/ directory).

File	Description
public.pem	RSA Public Key in PKCS#1 PEM format
private.pem	RSA Private Key in PKCS#1 PEM format, encrypted with AES-256-CBC and passphrase: passphrase123

View keys

• Private Key

  openssl rsa -in output/private.pem -text -noout

• Public key

  openssl rsa -pubin -in output/public.pem -text -noout

Author

Sidhant Sharma (Github)