Multithreaded Encrypted File Server & Client

---

MEFSC is a C++ based encrypted file server/client system that allows multiple users to securely store and retrieve files over a local or remote network. It's meant to act as your own private cloud, hosted on hardware you own and ideally accessed via Tailscale or other VPN.

Demo

Features

• Secure file upload/download via symmetric encryption
• User authentication via SQLite3
• File chunking and encryption with libsodium
• Multi-user access with thread pool for concurrent connections
• Client TUI with arrow-key menu (powered by FTXUI)
• Live server dashboard with real-time connection tracking (ANSI in-place refresh)
• Strongly-typed action enums instead of raw integer constants
• Tailscale compatibility for remote, secure connectivity

Encrypted files are stored on the server under per-user directories, and decrypted files are downloaded locally to the client's working directory.

---

How It Works

Authentication

• Users authenticate with credentials stored in a local SQLite3 database on the server.
• After successful login, the client presents an interactive menu:
  1. Upload File (encrypt + send)
  2. Download File (receive + decrypt)
  3. List Files
  4. Delete File
  5. Quit

Storage

• Server stores files encrypted at rest in:

• Client writes decrypted files to its current working directory.

Networking

• Uses TCP sockets for reliable, in-order chunk transmission because encrypted chunk shuffling would make decryption impossible.
• Everything is encrypted client-side before transmission, and decrypted after download.
• Server uses a thread pool (configurable size) to handle concurrent clients.

Cryptography

• Uses libsodium for all cryptographic operations.
• Key exchange via crypto_kx (Curve25519 + BLAKE2b).
• Session encryption via crypto_aead_chacha20poly1305.
• File encryption via crypto_secretstream_xchacha20poly1305 (chunked streaming).
• Passwords hashed with crypto_pwhash_str (Argon2id).

---

Dependencies

Ubuntu / Ubuntu-based:

sudo apt install sqlite3 libsqlite3-dev libsodium-dev cmake build-essential

Fedora

sudo dnf install sqlite-devel libsodium-devel cmake gcc-c++

FTXUI (v6.1.9) is fetched automatically by CMake via FetchContent — no manual install needed.

Building

cmake -B build -DCMAKE_BUILD_TYPE=Release
cmake --build build -j$(nproc)

Launching

1. Create a user (one-time setup)

cd build
./tests/gen_hash <password>        # prints a password hash
sqlite3 MEFSC_DB.db "CREATE TABLE users(username TEXT PRIMARY KEY, hashed_pswd TEXT);"
sqlite3 MEFSC_DB.db "INSERT INTO users VALUES('alice', '<paste-hash-here>');"
cd ..

2. Start the server

cd build && ./server

The server dashboard shows live metrics (uptime, total/live connections, active client FDs) updating in-place.

3. Start a client

./build/client_fs/client

Navigate the menu with arrow keys, select with Enter, or press q to quit.