devos/doc/secrets.md

Secrets

Secrets are managed using git-crypt and agenix so you can keep your flake in a public repository like GitHub without exposing your password or other sensitive data.

By default, everything in the secrets folder is automatically encrypted. Just be sure to run git-crypt init before putting anything in here.

Agenix

Currently, there is no mechanism in nix itself to deploy secrets within the nix store because it is world-readable.

Most NixOS modules have the ability to set options to files in the system, outside the nix store, that contain sensitive information. You can use agenix to easily setup those secret files declaratively.

agenix encrypts secrets and stores them as .age files in your repository. Age files are encrypted with multiple ssh public keys, so any host or user with a matching ssh private key can read the data. The age module will add those encrypted files to the nix store and decrypt them on activation to /run/secrets.

Setup

All hosts must have openssh enabled, this is done by default in the core profile.

You need to populate your secrets/secrets.nix with the proper ssh public keys. Be extra careful to make sure you only add public keys, you should never share a private key!!

secrets/secrets.nix:

let
  system = "<system ssh key>";
  user = "<user ssh key>";
  allKeys = [ system user ];
in

On most systems, you can get your systems ssh public key from /etc/ssh/ssh_host_ed25519_key.pub. If this file doesn't exist you likely need to enable openssh and rebuild your system.

Your users ssh public key is probably stored in ~/.ssh/id_ed25519.pub or ~/.ssh/id_rsa.pub. If you haven't generated a ssh key yet, be sure do so:

ssh-keygen -t ed25519

Note:

The underlying tool used by agenix, rage, doesn't work well with password protected ssh keys. So if you have lots of secrets you might have to type in your password many times.

Secrets

You will need the agenix command to create secrets. DevOS conveniently provides that in the devShell, so just run nix develop whenever you want to edit secrets. Make sure to always run agenix while in the secrets/ folder, so it can pick up your secrets.nix.

To create secrets, simply add lines to your secrets/secrets.nix:

let
  ...
  allKeys = [ system user ];
in
{
  "secret.age".publicKeys = allKeys;
}

That would tell agenix to create a secret.age file that is encrypted with the system and user ssh public key.

Then go into the secrets folder and run:

agenix -e secret.age

This will create the secret.age, if it doesn't already exist, and allow you to edit it.

If you ever change the publicKeys entry of any secret make sure to rekey the secrets:

agenix --rekey

Usage

Once you have your secret file encrypted and ready to use, you can utilize the age module to ensure that your secrets end up in /run/secrets.

In any profile that uses a NixOS module that requires a secret you can enable a particular secret like so:

{ self, ... }:
{
  age.secrets.mysecret.file = "${self}/secrets/mysecret.age";
}

Then you can just pass the path /run/secrets/mysecret to the module.

You can make use of the many options provided by the age module to customize where and how secrets get decrypted. You can learn about them by looking at the age module.

Note:

You can take a look at the agenix repository for more information about the tool.