File-Server

A secure file storage server with client-server architecture that provides encrypted file transfer and storage. Written in C using OpenSSL for encryption and SQLite for user management.

Table of Contents

• Features
• Libraries and Dependencies
• Installation
• Server Documentation
• Client Documentation
• Usage
• Security
• File Structure

Features

• Secure Authentication: Uses Argon2 for password hashing
• Encrypted File Transfer: All files are encrypted with AES-256-CBC before transfer
• Multi-user Support: Each user has isolated file storage
• Threaded Server: Handles multiple clients simultaneously
• Command-line Interface: Easy-to-use menu system
• Secure Storage: Files are stored encrypted on the server

Libraries and Dependencies

Required Libraries:

• OpenSSL (for encryption and TLS)
• SQLite3 (for user database)
• Argon2 (for password hashing)
• pthread (for threading)

Installation:

Linux (Debian/Ubuntu):

sudo apt-get update
sudo apt-get install libssl-dev libsqlite3-dev libargon2-dev

macOS (using Homebrew):

brew install openssl sqlite argon2

Windows:

1. Install vcpkg: https://vcpkg.io/en/getting-started.html
2. Then install dependencies:

vcpkg install openssl:x64-windows sqlite3:x64-windows argon2:x64-windows

Server Documentation

Configuration:

1. Generate SSL certificates:

   openssl req -x509 -newkey rsa:4096 -keyout server.key -out server.crt -days 365 -nodes

Commands:

The following is the protocol the client-server implements for communication

• auth username:password - Authenticate a user
• regi username:password - Register a new user
• list - List all user files
• dele filename - Delete a file
• upld filesize filename - Upload a file
• dwld filename - Download a file

Starting the Server:

./server

The server will prompt for a port number (default: 8080)

Client Documentation

Connection:

When starting the client, you'll need to provide:

• Server host (default: 127.0.0.1)
• Server port (default: 8080)

Menu Options:

1. Create Account: Register a new user
2. Login: Authenticate with existing credentials
3. Delete File: Remove a file from server
4. List Files: View all your files on server
5. Upload File: Send a file to the server (automatically encrypted)
6. Download File: Retrieve a file from server (automatically decrypted)
7. Exit: Close the connection

File Encryption:

• Files are encrypted with AES-256-CBC before upload
• The encryption key is derived from your password
• Files remain encrypted on the server, and are only decrypted client side

Usage

Server:

1. Compile:

   gcc -o server main.c user.c socket.c -lsqlite3 -lssl -lcrypto -largon2 -lpthread

2. Run:

   ./server

Client:

1. Compile:

   gcc -o client client.c -lssl -lcrypto

2. Run:

   ./client

Security

Implemented Protections:

• TLS 1.3 for all communications
• Argon2id for password hashing
• AES-256-CBC for file encryption
• Secure memory handling
• Protection against buffer overflows
• Per-user file isolation

Best Practices:

1. Use strong passwords
2. Keep your SSL certificates secure
3. Run server on trusted networks only
4. Regularly backup the database directory

File Structure

file-server/
│
├── server/
│   ├── main.c           - Main server logic
│   ├── user.c           - User authentication and management
│   ├── user.h           - User function declarations
│   ├── socket.c         - SSL/TLS and network operations
│   └── socket.h         - Socket function declarations
│
├── client/
│   └── client.c         - Client implementation
│   └── socket.c         - SSL/TLS and network operations
├── database/            - Automatically created
│   ├── users.db         - SQLite user database
│   └── [user_id]/       - Per-user encrypted files
│
├── server.crt           - your SSL certificate
├── server.key           - your SSL private key
└── README.md            - This file

Notes

• The server creates a directory structure automatically
• First run will create the SQLite database
• Each user gets their own directory under database/
• Files are stored with their original names but encrypted contents
• The server must be restarted to change ports