ChatSocket

A multi-room, end-to-end encrypted chat application written in C with both CLI and TUI clients. Designed for secure communication with AES-256-CTR encryption for rooms and X25519 key exchange for direct messages.

Features

• Multi-room Support: Create and join separate chat rooms
• End-to-End Encryption: AES-256-CTR with password-derived keys for room messages
• Password-Protected Rooms: Salted and hashed room passwords using SHA-256
• Direct Messages: Encrypted DMs between users using X25519 key exchange
• Ed25519 Identity: Persistent Ed25519 key pairs for user authentication
• TUI Client: Modern ncurses-based terminal UI with split panels
• CLI Client: Original raw-mode terminal client with real-time input
• TLS Support: Secure transport layer for all connections
• Persistence: Username, identity tokens, and DM nicknames saved locally

Quick Start

# Terminal 1: Start server
cd Server && ./run.sh

# Terminal 2: Start TUI client
cd Client && ./run_tui.sh

# Or CLI client
cd Client && ./run.sh

Connect to a remote server by passing the address:

cd Client && ./run_tui.sh 192.168.1.100:2077

Clients

TUI Client (client_tui)

Modern ncurses interface (~1450 lines) with:

• Split panel layout: messages on left (main area), sidebar on right (40 cols)
• Scrollable message history (Up/Down, j/k, PageUp/PageDown, g/G for Home/End)
• Mouse-free navigation with keyboard shortcuts
• Warm/muted color palette (muted cyan for messages, green border for lobby, cyan for rooms, magenta for DMs)
• Scroll position indicator in top bar
• Help overlay (press ? or F1)
• Persistent username saved to ~/.socketchat/username
• Persistent DM nicknames saved to ~/.socketchat/dm_nicks
• Auto-connect to server on startup if address saved

CLI Client (client)

Original raw-mode terminal client with:

• Real-time character input without pressing Enter
• Backspace support for editing
• Color-coded output
• Manual connection to any server address

Commands

Command	Description
/help	Display available commands
/name <username>	Set display name (persisted locally)
/create <room>	Create a public room
/create <room> -p <pass>	Create an encrypted room
/enter <room>	Join a room
/leave	Leave current room or DM
/rooms	List available rooms from server
/dm <1|token>	Start DM (use index, prefix, or full token)
/dmleave	Leave current DM session
/list	Refresh local DM history
/nick <n> <name>	Rename a DM by index
/token	Show your Ed25519 identity token
/clear	Clear current message view
/exit	Disconnect and quit

DM syntax supports multiple formats:

• /dm abcdef12 - use 8+ character token prefix
• /dm MyFriend - use saved nickname
• /dm <1> - use indexed reference

Architecture

Network

• Protocol: TCP/IPv4 with optional TLS
• Default Port: 2077
• Port override: Set PORT environment variable
• Message Size: 2048 bytes (configurable in code)

Cryptography

Room Encryption (AES-256-CTR)

• Algorithm: AES-256 in Counter Mode
• Key Derivation: SHA-256 of room password
• IV: 16-byte random per message
• Format: ENC:<base64-encoded-ciphertext>

Direct Messages (X25519)

• Key Exchange: X25519 Diffie-Hellman
• Identity Keys: Ed25519 key pairs
• Token Format: 64-character hex string
• Per-message encryption with unique nonces

Password Storage

• Hashing: SHA-256 with 10,000 iterations
• Salt: 16-byte random per room
• Format: <salt_hex>:<hash_hex>
• Constant-time comparison for verification

Server Components

• Thread-per-client model with detached threads
• Mutex-protected shared state for rooms
• Maximum 50 concurrent rooms
• Maximum 32 members per room
• Broadcast messaging within rooms
• Room entry/exit notifications

Client State

The TUI maintains several state files in ~/.socketchat/:

• username - Local username display
• identity - Ed25519 private key
• dm_nicks - Saved DM nicknames (JSON)
• server - Last connected server address

Building

Server

cd Server
gcc server.c ../Utils/socketUtil.c ../Utils/sha256.c -o server -lpthread
./server

Or use the provided script:

cd Server && ./run.sh

CLI Client

cd Client
gcc client.c ../Utils/socketUtil.c ../Utils/sha256.c ../Utils/aes.c -o client -lpthread -lssl -lcrypto
./client [address:port]

TUI Client

cd Client
gcc client_tui.c ../Utils/socketUtil.c ../Utils/sha256.c ../Utils/aes.c ../Utils/identity.c ../Utils/history.c -o client_tui -lpthread -lssl -lcrypto -lncurses
./client_tui [address:port]

Usage Examples

Basic Room Chat

1. Start server:

   cd Server && ./run.sh

2. Client A creates room:

   >>> /name Alice
   >>> /create project-alpha
   [*] Room 'project-alpha' created
   

3. Client B joins:

   >>> /name Bob
   >>> /enter project-alpha
   [*] Entered room 'project-alpha'
   

4. Chat:

   >>> Hello team!
   << Alice: Hello team!
   

Encrypted Room

1. Create password-protected room:

   >>> /create secrets -p mysecretpassword
   [*] Room 'secrets' created
   

2. Others must enter with password:

   >>> /enter secrets
   [*] Password: ********
   [*] Entered room 'secrets'
   

Direct Messages

1. Get your token:

   >>> /token
   [*] Token: abc123... (share this with friend)
   

2. Start DM using friend's token:

   >>> /dm abc123def456...
   [*] DM established
   

3. Or view DM list and use index:

   >>> /list
   >>> /dm 1
   

4. Rename DM for easy reference:

   >>> /nick 1 John
   

Security Considerations

Strengths

• End-to-end encryption - server cannot read message content
• AES-256-CTR - industry-standard encryption
• X25519 - modern elliptic curve key exchange
• Ed25519 - secure identity authentication
• Salted password hashing with high iteration count
• Constant-time password comparison
• Random IVs per message
• Keys never transmitted over network
• TLS option for transport security

Limitations

• Shared room passwords - all members have same key
• No message authentication (spoofing possible)
• Server logs encrypted metadata
• Username/room membership visible to server
• No forward secrecy

Troubleshooting

Connection Issues

• Check server is running: netstat -tlnp | grep 2077
• Verify firewall allows port 2077
• Test local connection first: telnet localhost 2077

Build Errors

• Install dependencies:

  # Debian/Ubuntu
  sudo apt install build-essential libssl-dev libncurses-dev
  
  # macOS
  brew install openssl ncurses

Runtime Issues

• Ensure ~/.socketchat/ directory exists for TUI
• Check terminal supports 256 colors: echo $TERM
• Try alternate TERM: TERM=screen-256color ./client_tui

License

MIT - use as you wish.