Branded SSH public keys

Prologue

There’s just something so elegant and human about presenting yourself in a certain way. Some people dress to their gender and others wear stylish clothes. Ultimately it’s all about human expression.

Photo by Mike Bird: Pexels

Some people even dress up their LinkedIn and GitHub profiles as much as they dress up in real life. To some degree, these are equally as valid forms of self expression.

Problem Space

A lot of the time I find myself sharing my SSH public key, it’s for access to a root account on some server with 5 other people’s keys in the authorized_keys file.

The two gripes I have are:

• Sometimes people are still using RSA, so their public key is quite long
• Having the comment just be some old gmail address is rather boring

How can I be more creative while keeping the key short and the file clean?

Branded .onion Vanity Addresses

For a while now, there’s projects like mkp224o out there that can generate a ton of .onion addresses and find one that matches a brand.

There are a few existing tools to brute force these ssh-ed25519 keys but I wanted to try making my own.

The First Attempt (golang)

Oh gourd, where do I even begin? This one is staying closed source forever and is written in the Go language.

I chose Go for these reasons:

• Automatic (easy) memory management
• Fast build times (rapid iteration)
• I know Go has high level abstractions for stuff like process launching
• Not Java

The approach was rather simple: how do we generate SSH keys? We use the command line tool, of course!

ssh-keygen -t ed25519 -C im@kunet.dev -f test -N \"\"

This would just run in a loop ad infinitum. No threads or goroutines.

As you can imagine this wasn’t very fast or good.

The Second Attempt (Rust)

Rust is a pretty cool language (and it’s all the rage nowadays). Fearless concurrency is cool and all and I decided it would be worth a shot.

The approach was pretty much the same and just launched 16 hardware threads each one spawning a ssh-keygen process, checking its output, and then trying until it finds a match.

This approach allowed for checking around 100 keys/sec on my computer. It also used up 100% of my CPU (not good!).

After writing this, I got sick and tired of being in a completely safe envrionment so came crawling back to Zig.

Zig (the best language)

Toying around with key generation in Rust made me feel horrible—relying on at least 6 crates just to make it work and a few more if I wanted to even attempt to get Ed25519 key pair generation working inside the app.

All the functionality (aside from the command line interface stuff) could luckily enough easily be done through the Zig standard library despite the language being much less mature and having far less of a userbase!

You can find the project here and now my new public SSH keys is:

ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIP8RbVheuZrUZmQv+5HvBxM0tGzo0wmK0cTZhTHKuNet im@kunet.dev

just for fun!