Are you running a server and occasionally meet some players you want to get rid of, but they keep coming back using alt accounts and a VPN? Well, now you've got the chance to identify their accounts based on a hardware ID instead of unreliable IPs, skins or behaviour!

What this mod does

This mod is registering an empty argument, making it required on clients if your server has it installed. Players who try to remove it from their modpack can't join your server.
When players join your server, the client calculates a semi-unique hash value based on the player's hardware, which is then stored by the server (<server root>/config/hwid), along with the account UUID.

What this mod doesn't do

Automatically ban people based on hardware IDs
Provide an easy way to find hardware IDs with multiple players in-game

How to use it then?

Check some example scripts further down below, I don't want to bury the following two points under codeblocks as they're quite important to read.

Privacy

While a hardware ID sounds invasive, it's way less confidental information than an IP address. The hardware ID is being calculated on the client using the SHA-256 algorithm, which is irreversible and therefore gives server operators no information on what hardware is being used. The hardware ID can only be used to tell unique hardware configurations apart.

Limitations

Hardware IDs are semi-unique. If players upgrade their computer or replace it entirely, it will change. Players can also have the same hardware ID, if they coincidentally have the same computer, for example a common pre-built. Serial numbers (if existing) are included during the hash calculation to minimize this occurence.
Dedicated troublemakers with knowledge of Java can decompile this mod and create an evil twin, sending a random or specific hardware ID every time they join.

Bash

#!/bin/bash

destination_path="/home/minecraftserver/config/hwid"
for file in "$destination_path"/*
do
    line_count=$(wc -l <"$file")  # Count the number of lines in the file
    if [ "$line_count" -gt 1 ]  # Check if the line count is greater than 1
    then
        echo ""; echo "$(basename "$file")"  # Print an empty line and the filename
        while IFS= read -r line  # Read each line from the file
        do
            uuid=${line}  # Assign the line to the variable 'uuid'
            response=$(curl -s https://sessionserver.mojang.com/session/minecraft/profile/${uuid})  # Send a request to the Mojang API to get the profile information
            name=$(echo "$response" | jq -r '.name')  # Extract the 'name' field from the API response using jq
            echo "${uuid} - ${name}"  # Print the UUID and the corresponding name
        done < "$file"  # Read from the file
    fi
done

Python 3

import os, json, requests

search = ""  # Set the search term, eg. username, UUID or parts of either

for filename in os.listdir("/home/minecraftserver/config/hwid"):  # Iterate over each file in the specified directory
    with open(f"/home/minecraftserver/config/hwid/{filename}", "r") as file:  # Open each file in read mode
        lines = file.readlines()  # Read all lines from the file
        if len(lines) > 1:  # Check if there are more than one line in the file
            result = ""  # Initialize the result string
            for line in lines:
                uuid = line.strip()  # Get the UUID from each line
                response = requests.get(f"https://sessionserver.mojang.com/session/minecraft/profile/{uuid}")  # Send a GET request to Mojang API to get player profile
                name = json.loads(response.text)['name']  # Extract the player name from the response
                result += f"{uuid} - {name}\n"  # Append UUID and name to the result string
            if search in result:  # Check if the search string is present in the result
                print(result)  # Print the result

HWID (Anti-Alts)