ElGamal Digital Signature Implementation

This project implements a Digital Signature Algorithm (DSA) based on the ElGamal signature scheme using a discrete logarithm problem (DLP). It provides both a graphical user interface and a command-line interface for key generation, file signing, and signature verification.

Contents

• ElGamal_signature.java — core implementation of the ElGamal signature scheme.
• Utils.java — utility class for file hashing using SHA-256.
• ElGamalGUITool.java — main application class with both GUI and CLI modes.

Features

• Generation of cryptographically secure parameters: a safe prime p = 2q + 1 where q is also prime.
• SHA-256 hashing of file content for signature binding.
• Support for metadata in keys: full name, email, and creation date.
• Base64-encoded public parameters in certificates for readability and compatibility.
• Swing-based GUI with three tabs:
  • Key Generation
  • File Signing
  • Signature Verification
• Fully functional CLI mode for scripting and automation.

Build and Run

1. Compilation

javac ElGamal_signature.java Utils.java ElGamalGUITool.java

2. Launch GUI (default)

java ElGamalGUITool

3. Command-Line Usage

# Generate key pair
java ElGamalGUITool -g

# Sign a file
java ElGamalGUITool -s document.txt private.key

# Verify a signature
java ElGamalGUITool -c document.txt document.txt.sig public.cert

# Show help
java ElGamalGUITool -h

Security Notes

• Uses Java’s SecureRandom for cryptographically strong randomness.
• Default key size: 512 bits (suitable for educational purposes; not recommended for production).

Important: This implementation wal developed as an educational project and is intended for demonstration purposes only. Do not use it in production systems without a thorough security review and parameter hardening.

File Formats

private.key

# ЗАКРЫТЫЙ КЛЮЧ ЭЦП - ХРАНИТЕ В СЕКРЕТЕ!
# Владелец: John Doe
name:John Doe
email:john@example.com
p:<hex>
g:<hex>
x:<hex>

public.cert

-----BEGIN ELGAMAL CERTIFICATE-----
Owner: John Doe
Email: john@example.com
Created: 2025-12-29
p:<base64>
g:<base64>
y:<base64>
-----END ELGAMAL CERTIFICATE-----

<file>.sig

-----BEGIN ELGAMAL SIGNATURE-----
File: document.txt
Owner: John Doe
Email: john@example.com
Hash:<base64>
r:<base64>
s:<base64>
-----END ELGAMAL SIGNATURE-----