word-of-wisdom-tcp-server

Problem/Purpose

Design and implement “Word of Wisdom” tcp server.

• TCP server should be protected from DDOS attacks with the Proof of Work (https://en.wikipedia.org/wiki/Proof_of_work), the challenge-response protocol should be used.
• The choice of the POW algorithm should be explained.
• After Proof Of Work verification, server should send one of the quotes from “word of wisdom” book or any other collection of the quotes.
• Docker file should be provided both for the server and for the client that solves the POW challenge

Why have I picked Hashcash algorithm?

The primary goal of a PoW algorithm is to make computational work time-consuming and resource-intensive, thus deterring attackers from performing Distributed Denial of Service (DDoS) attacks.

Hashcash

Algorithm Overview: Hashcash requires a party to perform a certain amount of computational work, which involves finding a partial hash collision. The work is typically to find a hash that starts with a specified number of leading zeros.

Reasons for Choosing Hashcash:

• Widely Adopted: Hashcash is a well-known and widely adopted PoW algorithm, used in various contexts, including email spam prevention.
• Simple yet Effective: The concept is straightforward, making it easy to implement and understand.
• Resource Intensive: The algorithm is computationally intensive, requiring significant CPU power to find a valid solution. This adds a layer of protection against DDoS attacks.
• Proven Track Record: Hashcash has been in use for years and has a proven track record of effectively mitigating certain types of attacks.

Summary

Ultimately, the choice depends on the specific security requirements of the system, the desired level of complexity, and the trade-offs between computational resources and memory usage. In this case, Hashcash is chosen for its simplicity, widespread use, and effectiveness in deterring DDoS attacks.

How to run a server?

Have a look into Dockerfile. It creates light-weight docker image on top of alpine where you have compiled binary /app/word-of-wisdom-tcp-server.

You can customize hostname and port if needed. Defaults: 0.0.0.0:8080

go run cmd/main.go -h

Usage: word-of-wisdom-tcp-server [OPTIONS]

Example: word-of-wisdom-tcp-server -p 8080

Options:
  -H, --hostname     listen on hostname (default "0.0.0.0")
  -p, --port         port to listen to (default "8080")
  -d, --difficulty   challenge difficulty (default "4")

Run a server in Docker container

# Build docker image
$ docker build -t word-of-wisdom-server .

# Run an app in docker container
$ docker run -p 8080:8080 word-of-wisdom-server
# 2024/01/22 12:54:01 Server listening on 0.0.0.0:8080

Run client

See Client's README

Example

# simple difficulty of 4 leading zeros in a hash
$ go run cmd/main.go
2024/01/29 13:35:41 server listening on 0.0.0.0:8080
2024/01/29 13:35:51 challenge: 4:qpJhEIs9xuwFyoiRkoLkkgCjHboTX4rxZvdZ3ovrO9u9KdTqiz
2024/01/29 13:35:51 nonce:  4212
2024/01/29 13:35:51 calculated hash:  00007d4419c11cf8d788d10059d2cb17ea148b7c49fd137385b54e7726273085
2024/01/29 13:35:51 quote sent to client: Quote 8
2024/01/29 13:35:52 challenge: 4:bFsazympmX2VUO7gaC2ia0epXM93FvWOvvAswtgXDqFzA4ApJL
2024/01/29 13:35:52 nonce:  23157
2024/01/29 13:35:52 calculated hash:  00005697d474e50497329c2569b83940f84d091d953b7193fda6663a0e2ddc90
2024/01/29 13:35:52 quote sent to client: Quote 6
2024/01/29 13:35:55 challenge: 4:MhosKzSnx6sfEwT4wgEbQ6koh8W2NlSQ6BDsPi2ZPBMgeb2mp6
2024/01/29 13:35:55 nonce:  19350
2024/01/29 13:35:55 calculated hash:  000076df79048fd4cdf9162f602da7adef989a910f5e1acea52c510ecc436f4b
2024/01/29 13:35:55 quote sent to client: Quote 7

# difficulty 6:
$ go run cmd/main.go -d 6
2024/01/29 13:36:02 server listening on 0.0.0.0:8080
2024/01/29 13:36:07 challenge: 6:1Rk5hiaXsUfgKA5TJ7IBzdCTteYRqkyWHFTDBqwU4wvizo4XrT
2024/01/29 13:36:19 nonce:  41214698
2024/01/29 13:36:19 calculated hash:  00000045ce84396aa29ae3936e77fb7e2d1fb80f09a71124b9153a62397c157b
2024/01/29 13:36:19 quote sent to client: Quote 9