Comparison of secret managing schemes

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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 rights (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.

This page was created from a discussion on Discourse and is likely never complete as people will start new projects to handle secrets in Nix(OS).


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.

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
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


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
terraform-nixos value of a nix expression stored in /var/keys/... owned by the keys unix group yes see [1]
scheme pre build build time /nix/store (or on disk) system activation runtime encryption technology "official" project notes
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 data is retrieved/decrypted with pass during evaluation time unencrypted in the store uses the password store (aka pass) which uses gpg no

builtins.exec discussion on discourse about build time secrets

builtins.readfile can read any file, builtins.exec can execute commands and thus query any kind of database or password manager etc. these functions return values in a nix expression, it is up to the user what happens to these values in configuration.nix see "build time" see "build time" see "build time" these functions just read files or execute commands, they do not provide anything inherently "secure" or "cryptographic" no the linked discussion is about a signing key that is only needed during build time and should not be stored in the nix store at all
scheme pre build build time /nix/store (or on disk) system activation runtime encryption technology "official" project notes