TCP Application With Encryption

Description

This application serves as a TCP client => server implementation and supports writing encrypted data. This application encrypts data from the client program (user-inputted data from stdin) and sends it to the server. The server then decrypts the data using the same key, tag, and nonce/IV generated from the client program and outputs the decrypted text.

Both the client and server take advantage of Chacha20_poly1305, a symmetric cipher. A shared key is used between the client and server. This key is located at /etc/tcpserver/key.txt by default. You may use the /client/genkey.c program to generate a key that is typically 32 bytes in size.

I wrote this application to practice Elixir and encryption. I plan to use a similar setup with my future Barricade Firewall project.

The Client

The client (/client/client.c) is written in C and uses a library named Libsodium for encryption and hashing.

Command Line Options

• --dst, -d => The IP of the server (default is "0.0.0.0").
• --port, -p => The port of the server (default is 3020).
• --key, -k => The path to the shared key file (default is "/etc/tcpserver/key.txt").

The Server

The server (/server/*) is written in Elixir and uses the ErLang Crypto module for decrypting data and hashing. The server utilizes GenServer.

Configuration

You may configure additional settings in /server/config/config.exs. Here is a brief description of each:

• ip => The IP for the server to listen on (default is {0, 0, 0, 0}).
• port => The port for the server to listen on (default is 3020).
• keypath => The path to the shared key file (default is "/etc/tcpserver/key.txt").

Note - The ip setting must be a tuple containing four elements and each element represents an octet. An example is {127, 0, 0, 1}.

Generating A Key

You may generate a key with the /client/genkey.c program.

Command Line Options

• --path, -p => The path to save the file to (default is "/etc/tcpserver/key.txt").

Requirements

Client

The client requires Libsodium to be installed on the system. Please read the installation instructions here.

Server

The server only requires ErLang and Elixir to be installed on the system. You shouldn't need to install anything else because we don't use any third-party dependencies. To be safe, you may execute the following:

cd server/
mix deps.get

Note - I installed ErLang, Elixir, and the server on a vanilla Ubuntu 20.04 VM and it ran the first time without any issues.

Compiling

Client and GenKey

You may use GCC to compile the client and genkey programs:

gcc -g client/client.c -o client -lsodium
gcc -g client/genkey.c -o genkey -lsodium

Please note you must link Libsodium which is done in the above via -lsodium.

Running

Client and GenKey

You can easily run the GenKey and Client programs via:

./genkey
...

./client

Server

Running the server is simple. Please execute the following commands:

cd server/
iex -S mix

Credits

• Christian Deacon - Created application.
• Dreae - Helped me understand the Chacha20_poly1305 cipher and encryption. He has been a HUGE help!