An SSH key is a public-private keypair that allows you to remotely access servers, in this case, the pubnix.
It is mandatory for pubnix registration since its the only secure way to let users access the pubnix.
Generating it is simple, and does not need a lot.
SSH is pre-installed on most systems. If it isn't, install it via your package manager.
From Windows 10 1809 onwards, ssh is built in to powershell.
For older versions of windows, you need to use putty to do so.
You can find a guide on it in the Digital Ocean Docs.
After that run the following in the terminal (or powershell.exe on windows)
ssh-keygen -t ed25519
Here, we recommend using ed25519 since its the latest and greatest format, however the default format (RSA) works too!
You can accept the defaults for the prompts, and add a password if you want to.
The password is an additional security layer, which would be needed to unlock the key.
Now, you can submit the <generated-key-name>.pub file in the pubnix registration form.
Note: the form only takes one key, but you can add more later by just appending them to ~/.ssh/authorized_keys