faraway-chal

README

Faraway Challenge

Contents

• Contents
• Algorithm
• Usage
• License

Algorithm

An implementation of a TCP server protected from DDoS attacks with the Proof of Work. When the clients solves the challenge, the server sends one of the quotes from Word of wisdom book. Docker files are provided for the server and the client sides.

Challenge-response protocol

I haven't found any RFC specification related to the protocol format and data flow on the Internet. So I've created a simple protocol by myself. This protocol works with binary encoded data in the following format:

• first byte: message id
• rest bytes: message structure in gob format.

There are a few structures, a structure type for each message.

Data flow

Client	Direction	Message	Server
Sends an initial message without data.	=>	challenge
	<=	challenge	Creates a hash by combining the secret key, client's IP address and nonce. Sends the challenge to the client.
Solves the challenge. Sends the solution to the server.	=>	solution
	<=	grant	Validates the client solution. If it's valid, grants the access (returns a poem), otherwise returns an error.
Prints the poem to console and exits.

POW algorithm

In my implementation I've used Hashcash PoW algorithm. It was chosen because of its simplicity and prevalence. The difficulty is hardcoded and equals 10.

Usage

# Firstly, run the server
$ scripts/server/run.sh

# Then, run the client
$ scripts/client/run.sh

# Or run the applications as a Docker Container
$ sudo docker compose up

License

Licensed under the MIT license.

Author

Alexander Mac