🔐 Secure P2P Chat Application

A comprehensive secure peer-to-peer (P2P) chat application built with Java that implements enterprise-grade cryptographic security. This application features end-to-end encryption, perfect forward secrecy, digital signatures, and automatic peer discovery in a fully decentralized architecture.

🌟 Key Features

🔒 Advanced Security

• RSA 2048-bit Encryption - Initial handshake and key exchange
• Perfect Forward Secrecy (PFS) - Diffie-Hellman ephemeral key exchange
• AES Encryption - Message content encryption after DH exchange
• Digital Signatures - SHA256withRSA for message authenticity
• Message Freshness Validation - Timestamp-based replay attack protection
• Salted Password Hashing - Secure user authentication

🚀 User Experience

• Automatic Peer Discovery - No manual IP/port configuration needed
• GUI Interface - User-friendly graphical interface available
• Terminal Interface - Command-line interface for advanced users
• Real-time Messaging - Instant secure communication
• Chat Request System - Accept/reject incoming chat requests
• Online User Listing - View all available peers

🏗️ Architecture

• True P2P - No central server required
• Decentralized Registry - Peer discovery through local file system
• Multi-threaded - Concurrent handling of multiple connections
• Cross-platform - Java-based for universal compatibility

📋 Requirements

• Java JDK 11 or higher
• Terminal/Command Prompt for command-line interface
• Git (optional, for cloning repository)

🚀 Quick Start

1. Compilation

Navigate to the project directory and compile all Java files:

javac *.java

2. User Registration

Register users before chatting:

java RegisterUser

Example:

Enter username: alice
Enter password: mySecurePassword123
User registered successfully!

This creates:

• keys/alice.pub (RSA public key)
• keys/alice.pri (RSA private key)
• Adds user credentials to users.txt

Repeat for additional users (e.g., bob, charlie).

3. Starting the Application

Option A: Terminal Interface

java PeerChat

User Experience:

Enter username: alice
Enter password: mySecurePassword123
Authentication successful!
Enter your listening port: 5000
Listening for incoming connections on port 5000...

Enter 'list' to view online users or username to chat (or 'exit'): list

=== Online Peers ===
 - bob
 - charlie

Enter 'list' to view online users or username to chat (or 'exit'): bob
Start chatting with bob. Type 'quit' to end chat.
[You] > Hello Bob!
[bob] > Hi Alice! How are you?

Option B: GUI Interface

java ChatAppLauncher

Features a complete graphical interface with:

• Login window with authentication
• Registration dialog for new users
• Main chat window with peer discovery
• "List Online Users" button for peer selection
• Automatic connection handling

🔧 How It Works

Cryptographic Flow

1. Authentication - User credentials verified with salted hash
2. RSA Handshake - Initial secure channel establishment
3. DH Key Exchange - Ephemeral keys generated for PFS
4. AES Communication - All messages encrypted with shared secret
5. Digital Signatures - Every message signed and verified

Peer Discovery

1. Registration - Peers register IP:PORT in peers.txt
2. Discovery - Users can list all online peers
3. Connection - Connect by username (automatic IP/port lookup)
4. Request System - Chat requests must be accepted

Message Security

• End-to-End Encryption - Only sender/receiver can read messages
• Perfect Forward Secrecy - Each session uses unique keys
• Non-repudiation - All messages digitally signed
• Integrity Protection - Tampering detection via signatures

📁 Project Structure

Secure-P2P-ChatApp/
├── PeerChat.java           # Main P2P chat application
├── CryptoUtils.java        # Cryptographic utilities
├── UserManager.java        # User authentication system
├── RegisterUser.java       # User registration utility
├── MessageLogger.java      # Encrypted message logging
├── LogViewer.java         # Log file viewer
├── LoginFrame.java        # GUI login interface
├── RegistrationDialog.java # GUI registration dialog
├── MainChatFrame.java     # GUI main chat window
├── ChatAppLauncher.java   # GUI application launcher
├── keys/                  # RSA key storage directory
├── users.txt             # User credential database
├── peers.txt             # Peer registry file
├── auth_log.txt          # Authentication log
└── encrypted_messages.txt # Encrypted message log

� Logging and Monitoring

Authentication Logs

# View authentication attempts
cat auth_log.txt

Message Logs

# View encrypted message history
java LogViewer

Real-time Monitoring

All cryptographic operations and peer connections are logged with timestamps for security auditing.

🛡️ Security Implementation Details

Encryption Standards

• RSA-2048 - Asymmetric encryption for initial handshake
• AES-256 - Symmetric encryption for message content
• SHA-256 - Cryptographic hashing for signatures
• PBKDF2 - Password-based key derivation

Security Measures

• Replay Protection - 60-second message freshness window
• Key Rotation - New DH keys for each chat session
• Signature Verification - All messages cryptographically verified
• Secure Random - Cryptographically secure random number generation

Attack Mitigation

• Man-in-the-Middle - RSA public key authentication
• Replay Attacks - Timestamp validation
• Message Tampering - Digital signature verification
• Password Attacks - Salted hash storage

🎯 Usage Examples

Terminal Workflow

# Start first user
java PeerChat
# alice, password, port 5000

# Start second user
java PeerChat
# bob, password, port 6000

# Bob connects to Alice
Enter 'list' to view online users or username to chat: alice
Start chatting with alice. Type 'quit' to end chat.
[You] > Hello Alice!

GUI Workflow

1. Launch java ChatAppLauncher
2. Login with credentials
3. Click "List Online Users"
4. Select peer and start chatting