Comparison of secret managing schemes

Introduction

Sometimes you need to use secrets in your system configuration. Those can range from user passwords and Wifi passwords over private keys (ssh, ssl, ...) to API tokens and similar things. Normally one would store this kind of information in files with restricted access writes (only readable by some Unix user) or even encrypt them on disk. Nix and NixOS store a lot of information in the world-readable Nix store where at least the former is not possible. People who track their configuration with Git (or use Flakes) might even want to store these secrets in the Git repository but still upload the repository somewhere.

In these cases it is necessary to think about a suitable scheme to manage the relevant secrets so that they are only readable by the right people or machines. This page tries to give an overview of different schemes that can be used and outlines the aims, requirements and implications of each.

Definitions

The properties of the different schemes that are listed in the table below are explained in detail here. You are welcome to add more schemes (rows) to the table; please try to fill in as many of the properties as you can. If you add a new column please try to fill it for all existing rows as much as possible.

scheme: the name of the scheme, if possible a link to the official website or source, maybe a short description
pre build: Where does the secret reside before the configuration is build? In a file, in a nix expression, in an external database (password manager)? Is it encrypted?
build time: what happens at build time, is the secret decrypted or encrypted, which master passwords, passphrases or helper programs are needed
in the store (on disk): Is the data stored in /nix/store after the build? Is it encrypted. This has implications for reproducability. If a secret is not stored in the nix store it might be more difficult to recreate an old system configuration
system activation: what happens to the data at system activation, that is at boot time or when nixos-rebuild switch or --rollback is executed
runtime: where does the secret reside after system activation, is it encrypted, who can read it
encryption technology: which programs or tools are used for encryption or decryption of secrets; whether ssh-agent, gpg-agent or similar are supported
"official" project: whether this is a published software project (maybe even actively developed) or just some notes in a forum or a blog entry

Comparison

In case this table is difficult to read with the default theme, try the vector theme.

Comparison of secret managing schemes
scheme	pre build	build time	`/nix/store` (or on disk)	system activation	runtime	encryption technology	"official" project	notes
NixOps keys (is there a better link to the docs that does not depend on a hydra build id?)	plain value in a nix expression		not stored in the store	N/A the user has to run `nixops` `send-keys` to create these files after a (manual) reboot (not required after every reboot if destDir is persistent storage)	unencrypted in `/run/keys/...` or configured path		yes	"out of band", secret management happens outside of `nixos-rebuild`
agenix	encrypted raw files, `agenix` CLI encrypts with the user and host ssh key		encrypted	decryption with the host ssh key	unencrypted in `/run/secrets/...` or configured path	uses `age` with ssh user and host keys, does not support `ssh-agent`	yes
sops-nix	encrypted with gpg or ssh key		encrypted	decryption	stored in `/run/secrests/` with configurable permissions	uses sops	yes	can be used with NixOps, `nixos-rebuild`, krops, morph, nixus
krops	stored in the password store					uses the password store (aka `pass`) which uses gpg	yes
`builtins.readfile` on discourse							no
`builtins.exec` on discourse							no
Blog entry 1	plain text file (unencrypted), can be stored in git	encryption	encrypted in the store	decrypted by a systemd unit		uses age and the ssh host key of the target machine	no, blog, and config repository	Warning: plaintext is unencrypted in the nix store of the deployment machine
Blog entry 2 wrapper around `pass` based on nix-plugins	stored in the password store					uses the password store (aka `pass`) which uses gpg	no