classified

A simpler NixOS secrets management system.

Problem

There’re some secrets management systems for NixOS (agenix, sops-nix), but they require kinda complicated setup. In many cases it’s enough to just decrypt all the secrets with root-readable key file present on disk (if someone has root access to your computer, you’re probably already royally fucked).

Solution

Use a simple encryption program and put the config into a NixOS module. Just like this:

# flake.nix
{
  inputs = {
    classified = {
      url = "github:GoldsteinE/classified";
      # to avoid having one more copy of nixpkgs
      inputs.nixpkgs.follows = "nixpkgs";
      # you can also do this with naersk
    };
  };
  outputs = { nixpkgs, classified, ... }: {
    nixosConfigurations.your-hostname = nixpkgs.lib.nixosSystem rec {
      system = "x86_64-linux";
      modules = [
        # other modules here
        ./configuration.nix
        classified.nixosModules."${system}".default
      ];
    };
  };
}

and then

# configuration.nix
{
 classified = {
   # Default is `/var/secrets`
   targetDir = "/var/classfied";
   keys = {
     first = "/path/to/first.key";
     second = "/path/to/second.key";
   };
   files = {
     top-secret = {
       # You can omit the `key` attribute if you have exactly one key configured
       key = "first";
       encrypted = ./encrypted-file;
       # Default is `400`
       mode = "440";
       # Defaults are `root:root`
       user = "nginx";
       group = "nogroup";
     };
   };
 };
}

Generating keys and encrypting data

# (as root)
umask 377  # so the key file has the right permissions
classified gen-key > /path/to/key
cat /path/to/key  # key is just 24 words, so you can write it down
umask 022  # it's ok for encrypted data to be world-readable
classified encrypt --key /path/to/key /path/to/secret-data > /path/to/encrypted-data
# if you ever want to manually decrypt it
classified decrypt --key /path/to/key /path/to/encrypted-data

What’s inside?

• XChaCha20-Poly1305 which is proven secure. The nonce is chosen randomly for every encrypted file.

• A fresh tmpfs is created on every decryption, so old secrets are not available.

• No temporary files are written, no Rust unsafe code is used, and the codebase is small and easy to audit yourself.

• It attempts to zeroize any keys and decrypted files before deallocating memory.

So it’s secure?

I mean...

• It didn’t pass any kind of professional security review.

• Zeroizing memory is hard and should be considered best-effort.

So (as with any cryptography project) — use at your own risk.