sops-nix

Atomic secret provisioning for NixOS based on sops.

How it works

Sops-nix decrypts secrets sops files on the target machine to files specified in the NixOS configuration at activation time. It also adjusts file permissions/owner/group. It uses either age or GPG keys for decryption, where both types can be derived from ssh host keys. In future we will also support cloud key management APIs such as AWS KMS, GCP KMS, Azure Key Vault or Hashicorp's vault.

Features

• Compatible with all NixOS deployment frameworks: NixOps, nixos-rebuild, krops, morph, nixus
• Version-control friendly: Since all files are encrypted they can directly committed to version control. The format is readable in diffs and there are also ways of showing git diffs in cleartext
• Works well in teams: sops-nix comes with nix-shell hooks that allows quickly import multiple people to import all used keys. The cryptography used in sops is designed to be scalable: Secrets are only encrypted once with a master key instead of each machine/developer key.
• CI friendly: Since sops files can be added to the Nix store without leaking secrets, a machine definition can be built as a whole.
• Atomic upgrades: New secrets are written to a new directory which replaces the old directory in an atomic step.
• Rollback support: If sops files are added to Nix store, old secrets can be rolled back. This is optional.
• Fast: Unlike solutions implemented by NixOps, krops and morph there is no extra step required to upload secrets
• Different storage formats: Secrets can be stored in YAML, JSON or binary.
• Minimize configuration errors: sops files are checked against the configuration at evaluation time.

Demo

There is a configuration.nix example in the deployment step of our usage example.

Supported encryption methods

sops-nix supports two basic ways of encryption, gnupg and age. Gnupg is based on gnupg (duh) and encrypts against gnupg public keys. Private gnupg keys may be used to decrypt the secrets on the target machine. The tool

ssh-to-pgp

The other method is age which is based on age. A tool is provided with sops-nix that can convert ssh host or user keys in ed25519 format to age keys.

Usage example

1. Install nix-sops

Choose one of the following methods:

niv (Current recommendation)

First add it to niv:

$ niv add Mic92/sops-nix

Then add the following to your configuration.nix in the

imports

{
  imports = [ "${(import ./nix/sources.nix).sops-nix}/modules/sops" ];
}

nix-channel

As root run:

$ nix-channel --add https://github.com/Mic92/sops-nix/archive/master.tar.gz sops-nix
$ nix-channel --update

Then add the following to your configuration.nix in the

imports

{
  imports = [  ];
}

fetchTarball

Add the following to your configuration.nix:

{
  imports = [ "${builtins.fetchTarball "https://github.com/Mic92/sops-nix/archive/master.tar.gz"}/modules/sops" ];
}

or with pinning:

{
  imports = let
    # replace this with an actual commit id or tag
    commit = "298b235f664f925b433614dc33380f0662adfc3f";
  in [ 
    "${builtins.fetchTarball {
      url = "https://github.com/Mic92/sops-nix/archive/${commit}.tar.gz";
      # replace this with an actual hash
      sha256 = "0000000000000000000000000000000000000000000000000000";
    }}/modules/sops"
  ];
}

Flakes

If you use experimental nix flakes support:

{
  inputs.sops-nix.url = github:Mic92/sops-nix;
  # optional, not necessary for the module
  #inputs.sops-nix.inputs.nixpkgs.follows = "nixpkgs";

  outputs = { self, nixpkgs, sops-nix }: {
    # change yourhostname to your actual hostname
    nixosConfigurations.yourhostname = nixpkgs.lib.nixosSystem {
      # change to your system:
      system = "x86_64-linux";
      modules = [
        ./configuration.nix
        sops-nix.nixosModules.sops
      ];
    };
  };
}

2a. Generate a GPG key for yourself

This is only needed when you plan to use the gnupg encryption. When using age, you can skip to step 2b instead.

First generate yourself a GPG key or use nix-sops conversion tool to convert an existing ssh key (we only support RSA keys right now):

$ nix-shell -p gnupg -p ssh-to-pgp --run "ssh-to-pgp -private-key -i $HOME/.ssh/id_rsa | gpg --import --quiet"
2504791468b153b8a3963cc97ba53d1919c5dfd4
# This exports the public key
$ nix-shell -p ssh-to-pgp --run "ssh-to-pgp -i $HOME/.ssh/id_rsa -o $USER.asc"
2504791468b153b8a3963cc97ba53d1919c5dfd4

If you get:

ssh-to-pgp: failed to parse private ssh key: ssh: this private key is passphrase protected

then your ssh key is encrypted with your password and you need to create an unencrypted copy temporarily:

$ cp $HOME/.ssh/id_rsa /tmp/id_rsa
$ ssh-keygen -p -N "" -f /tmp/id_rsa
$ nix-shell -p gnupg -p ssh-to-pgp --run "ssh-to-pgp -private-key -i /tmp/id_rsa | gpg --import --quiet"

The hex string printed here is your GPG fingerprint that can written to your

.sops.yaml

# This example uses yaml anchors which allows to name keys
# and re-use for multiple keys in a flexible way.
# Also see https://github.com/Mic92/dotfiles/blob/master/nixos/.sops.yaml
# for a more complex example
keys:
  - &admin 2504791468b153b8a3963cc97ba53d1919c5dfd4
creation_rules:
  - path_regex: secrets/[^/]+\.yaml$
    key_groups:
    - pgp:
      - *admin

If you have generated a GnuPG key directly you can get your fingerprint like this:

$ gpg --list-secret-keys
/tmp/tmp.JA07D1aVRD/pubring.kbx
-------------------------------
sec   rsa2048 1970-01-01 [SCE]
      9F89C5F69A10281A835014B09C3DC61F752087EF
uid           [ unknown] root 

The fingerprint here is

9F89C5F69A10281A835014B09C3DC61F752087EF

2b. Generate a SSH and age key for yourself

This is only needed when you plan to use the age encryption. When using gnupg, you need to go back to step 2a.

sops-nix in age mode requires you to have an age key. You can generate one like this:

$ mkdir -p ~/.config/sops/age
$ age-keygen -o ~/.config/sops/age/keys.txt

If you have an ssh key in

ed25519

ssh-keygen -t ed25519

$ mkdir -p ~/.config/sops/age
$ nix-shell -p ssh-to-age --run "ssh-to-age -private-key -i ~/.ssh/id_ed25519 > ~/.config/sops/age/keys.txt"

Converting the public key to the age format works like this:

console
$ nix-shell -p ssh-to-age --run " ssh-to-age < ~/.ssh/id_ed25519.pub "

or like this

$ nix-shell -p ssh-to-age --run "ssh-add -L | ssh-to-age"

If you get:

failed to parse ssh private key: ssh: this private key is passphrase protected

then your ssh key is encrypted with your password and you need to create an unencrypted copy temporarily:

$ cp $HOME/.ssh/id_ed25519 /tmp/id_ed25519
$ ssh-keygen -p -N "" -f /tmp/id_ed25519
$ nix-shell -p ssh-to-age --run "ssh-to-age -private-key -i /tmp/id_ed25519 > ~/.config/sops/age/keys.txt"

3a. Get a PGP Public key for your machine

The easiest way to add new hosts is using ssh host keys (requires openssh to be enabled). Since sops does not natively supports ssh keys yet, nix-sops supports a conversion tool to store them as gpg keys.

$ ssh [email protected] "cat /etc/ssh/ssh_host_rsa_key" | nix-shell -p ssh-to-pgp --run "ssh-to-pgp -o server01.asc"
# or with sudo
$ ssh [email protected] "sudo cat /etc/ssh/ssh_host_rsa_key" | nix-shell -p ssh-to-pgp --run "ssh-to-pgp -o server01.asc"
0fd60c8c3b664aceb1796ce02b318df330331003
# Or just read them locally (or in a ssh session)
$ nix-shell -p ssh-to-pgp --run "ssh-to-pgp -i /etc/ssh/ssh_host_rsa_key -o server01.asc"
0fd60c8c3b664aceb1796ce02b318df330331003

Also the hex string here is the fingerprint of your server's gpg key that can be exported append to

.sops.yaml

keys:
  - &admin 2504791468b153b8a3963cc97ba53d1919c5dfd4
  - &server 0fd60c8c3b664aceb1796ce02b318df330331003
creation_rules:
  - path_regex: secrets/[^/]+\.yaml$
    key_groups:
    - pgp:
      - *admin
      - *server

If you prefer having a separate GnuPG key, see Use with GnuPG instead of ssh keys.

3b. Get a age Public key for your machine

The

ssh-to-age

console
$ nix-shell -p ssh-to-age --run 'ssh-keyscan my-server.com | ssh-to-age'
$ nix-shell -p ssh-to-age --run 'cat /etc/ssh/ssh_host_ed25519_key.pub | ssh-to-age'

4. Create a sops file

To create a sops file you need write a

.sops.yaml

sops-nix automates importing gpg keys with a hook for nix-shell allowing public keys to be shared via version control (i.e. git):

# shell.nix
with import  {};
let
  sops-nix = builtins.fetchTarball {
    url = "https://github.com/Mic92/sops-nix/archive/master.tar.gz";
  };
in
mkShell {
  # imports all files ending in .asc/.gpg
  sopsPGPKeyDirs = [ 
    "./keys/hosts"
    "./keys/users"
  ];
  # Also single files can be imported.
  #sopsPGPKeys = [ 
  #  "./keys/users/mic92.asc"
  #  "./keys/hosts/server01.asc"
  #];

This hook can also import gpg keys into its own seperate
gpg keyring instead of using the default one. This allows
to isolate otherwise unrelated server keys from the user gpg keychain.
By uncommenting the following lines, it will set GNUPGHOME
to .git/gnupg.
Storing it inside .git prevents accedentially commiting private keys.
After setting this option you will also need to import your own
private key into keyring, i.e. using a a command like this
(replacing 0000000000000000000000000000000000000000 with your fingerprint)
$ (unset GNUPGHOME; gpg --armor --export-secret-key 0000000000000000000000000000000000000000) | gpg --import
  #sopsCreateGPGHome = true;
To use a different directory for gpg dirs set sopsGPGHome
  #sopsGPGHome = "${toString ./.}/../gnupg";
  nativeBuildInputs = [
    (pkgs.callPackage sops-nix {}).sops-import-keys-hook
  ];
}

Our directory structure looks like this:

$ tree .
.
├── keys
│   ├── hosts
│   │   └── server01.asc
│   └── users
│       └── mic92.asc

After that you can open a new file with sops

$ nix-shell -p sops --run "sops secrets.yaml"

This will start your configured editor In our example we put the following content in it:

example-key: example-value

Nesting the key results in the creation of directories. These directories will be owned by root:keys and have permissions 0751.

yaml
myservice:
  my_subdir:
    my_secret: example value

As a result when saving the file the following content will be in it:

example-key: ENC[AES256_GCM,data:7QIOMLd2kZkeVVpH0Q==,iv:ROh+J59ZM6BtjZLhRj1Ylk6ROEvsiX6/UR8obHX8YcQ=,tag:QOiFoHKyGFBkhr9lcWBB3Q==,type:str]
sops:
    kms: []
    gcp_kms: []
    azure_kv: []
    lastmodified: '2020-07-13T09:09:14Z'
    mac: ENC[AES256_GCM,data:BCwTBxaW6qINVfixC32EEYrlqPvGz47wF+o/vNPqcwed1HPwZezlNy7Z4NFLbRcCLAELyeMqkJ+fi9XCWvnT3UvfwB45COpz/xZphURt3gyCVOyd9mT/s9cJ1O9vNy5iKblqCae2X0CTKee/GxJ0G725LDOL4r+oHM1+WWEInWo=,iv:S43qegidSqcaUaDjvQpEQj/qvF/OZcW32Yo05CfyTUs=,tag:npj5auJXZrg7jQwYSjC6Vg==,type:str]
    pgp:
    -   created_at: '2020-07-13T08:34:30Z'
        enc: |
            -----BEGIN PGP MESSAGE-----

        hQIMAysxjfMwMxADAQ//SyBLvbpyuoTGCZCtoJyaFzZ+vCKWZaD7dCZEURRyNKFV
        87wZyNO/rwtA1jP64Smqy0q2R8iZfoN0v5oVvtj2y5wFECs8Q5nONCVP4rs9nTRK
        n46w0v2UE2GqIWStFE7Mpv11qdZaMDoNGXq+n6s/uA2mwSYIVvzcWwhKvyKrMNrd
        iOlfCKl4QTaGgGupZqmT2S00AEMJzY5lohvtzAC1TlnXGXhetDyCHtkoN/NKZDU7
        m7j1/pvlIwxTQKeA3FKuxDJDYk+p3+W/EgwEchYDzjo+5A529J/tuIfXWBOF7BAV
        ZiVVWISTahky/ioOMatNBAttu0lBGlSkovkbqIVsbTG7nF1wzGdToCxZmwQveEj7
        0N8ZzocDkOXqS71LW+X2HYSeywxNUbg/S6MrHrZN8MOp5qnGztm8yrKW2gDDe+Nl
        nqJJ4lGg5CbODoDmhbPPof9tmWkykFmQSqmkjs4pcomcNthmcQvPVy75pnXEN9Wo
        0cDRnHtgROCJLqfv1AsXWkSxtmZRMMQ1yKJIPVFUHSPodgAoTyA81sHi66RypDOV
        KezX6sW8UuTZ7q1oPcJFpaaHrpIHDn+bqPGMfhu4NVXFusdb7MPxtxlKflhTdc8B
        xzlrB6+LdnCaeN+KqB6DOvmiPP3nC91zflO1SpMY3yUOnTFDKZG7wnVjidyIuMvS
        UAHk6rhsBEJleAn5f4AuBVWtWLuvS4t1g9Lhci3833f7XNp+GFNy05UOsmUo9upr
        cgqaa2teuy2cbUtzS6gLBbcMA7SEs5MDYHjq6le/pwKv
        =ZYPM
        -----END PGP MESSAGE-----
    fp: 0FD60C8C3B664ACEB1796CE02B318DF330331003
-   created_at: '2020-07-13T08:34:30Z'
    enc: |
        -----BEGIN PGP MESSAGE-----

        hQIMAysxjfMwMxADARAAqbkG7+WZIDDHNjFp4mcabdGcKaTenJmAQKJjk4vnAWZD
        5Y6yInTldxldsFNvPcVmjZp/nM1otyH0MEHrurl5LX+BuUj8hRIE0ZFnNU0hNmyd
        toiwTE4GF1/otYFOPb9WnhDt+g6Y0ORuV/ZMSvP8PIu5/UnTeCkbZR/VudOvUq/m
        qF013M3q7UKssW4aReO2goFEhLjm8GfWksCuiGYKoHdJKzFAPYNhoxnxU3n43Oxp
        wz7QYFI0aA7RLZph70WjUNBun5+y4UyEJ8uNZ+cgVBeHQLqVdFUuejdzWK0d79Mr
        5D9fxgSsPMz7yUMMdPl0T4rrAsZ977pftI9+JofqMN+u9UzUJwfTjnbCxlob39/t
        bfORkanzU8BNUCxpHyyqau921AUtfcqV9Y9Hf+qwxgVRVKgfETOqN376A1nhrYsf
        Mhvmcsk/rDssiRSIu11/mZwifcpALnS8WgO5tK+e/454ANqsiEdSRVogWBTzcIIs
        trm/6kwsTl7COzK0ThUKIb6aOfb910JQKaYq93qWqF1fceIf49Ubz9NVZc80J0an
        OiAaVGS0IOGI1ua8zciY7m+rr1BlrqJFtUm7hd8C9fMaF8YdB2SXgW8/HPGL8uTd
        f9ASg9TMSxhr7wjdqWp4EXXxdB6p4FXai9XBbgAJ2tKcS6AV6QmRVMoITZ7uZpvS
        UAG4nIgey9A57C8DSnt5zVPtxAsjDNiMubLUnHzTEJEJyQH5j2E41teujycOOAye
        I/UHMfpxSgrFfS8JJHYrJO0JQq/maBZi/VzZCl/G3IMn
        =Xls9
        -----END PGP MESSAGE-----
    fp: 0FD60C8C3B664ACEB1796CE02B318DF330331003
-   created_at: '2020-07-13T08:34:30Z'
    enc: |
        -----BEGIN PGP MESSAGE-----

        hQEMA5w9xh91IIfvAQf+I1FDo7rglcA6EF7jmQ0pq9FwYR/Dd9+4pu4mxUofQawj
        YsXPToVvyOKFrs1BZzW3Idyn5U/oXnkPN0qNK30DKir/wCt9OBqHHuhlo80OR2nS
        G2ZvHOJKEW3W5Hs2yT1e1MQxznI1lGFrsj6xgZAnKtK3Y6iy48XZ9pTw4Fxjkixw
        NppHtYrMj30mwV9XFAer0EfGlV2AIi70xBZ2inYAzPU2SpLEEoGyztjIeSS4VfhQ
        fnKSx3UjlVIix65s2ky0JqbL1wI+FPKNt2hWupW+M7en8BJ5VfAcbU7n0ZuQnaFx
        YPErw3agfhw1bNnqXh0y5aZ9sswt/Jy+IRkMJHLcqNJQAREdKgGmkW8wO2dngYYL
        IwLyChHJfcSnixboVcW5CIbfmIbOdgfEk2tdSiX1tJIA6qeeJz+D8UbR47nIdIw2
        ZoID5dEUiDgikopjdqWk+zk=
        =43hf
        -----END PGP MESSAGE-----
    fp: 9F89C5F69A10281A835014B09C3DC61F752087EF
unencrypted_suffix: _unencrypted
version: 3.5.0

5. Deploy

If you derived your server public key from ssh, all you need in your configuration.nix is:

{
  imports = [  ];
  # This will add secrets.yml to the nix store
  # You can avoid this by adding a string to the full path instead, i.e.
  # sops.defaultSopsFile = "/root/.sops/secrets.yaml";
  sops.defaultSopsFile = ./secrets.yaml;
  sops.secrets.example-key = {};
  # This is using ssh keys in the age format:
  sops.age.sshKeyPaths = [ "/etc/ssh/ssh_host_ed25519_key" ];
  # This is using an age key that is expected to already be in the filesystem
  sops.age.keyFile = "/var/lib/sops-nix/key.txt";
  # This will generate a new key if the key specified above does not exist
  sops.age.generateKey = true;
  sops.secrets."myservice/my_subdir/my_secret" = {};
}

On

nixos-rebuild switch

/run/secrets/example-key

$ cat /run/secrets/example-key
example-value

/run/secrets

/etc/secret.d/1

$ ls -la /run/secrets
lrwxrwxrwx 16 root 12 Jul  6:23  /run/secrets -> /run/secrets.d/1

Set secret permission/owner and allow services to access it

By default secrets are owned by

root:root

/run/secrets.d

root

keys

$ ls -la /run/secrets.d/1
total 24
drwxr-x--- 2 root keys   0 Jul 18 15:35 .
drwxr-x--- 3 root keys   0 Jul 18 15:35 ..
-r-------- 1 root root  20 Jul 18 15:35 borgbackup

The secrets option has further parameter to change secret permission. Consider the following nixos configuration example:

{
  # Permission modes are in octal representation,
  # the digits reprsent: user|group|owner
  # 7 - full (rwx)
  # 6 - read and write (rw-)
  # 5 - read and execute (r-x)
  # 4 - read only (r--)
  # 3 - write and execute (-wx)
  # 2 - write only (-w-)
  # 1 - execute only (--x)
  # 0 - none (---)
  sops.secrets.example-secret.mode = "0440";
  # Either a user id or group name representation of the secret owner
  # It is recommended to get the user name from `config.users..name` to avoid misconfiguration
  sops.secrets.example-secret.owner = config.users.nobody.name;
  # Either the group id or group name representation of the secret group
  # It is recommended to get the group name from `config.users..group` to avoid misconfiguration
  sops.secrets.example-secret.group = config.users.nobody.group;
}

To access secrets each non-root process/service needs to be part of the keys group. For systemd services this can be achieved as following:

{
  systemd.services.some-service = {
    serviceConfig.SupplementaryGroups = [ config.users.groups.keys.name ];
  };
}

For login or system users this can be done like this:

{
  users.users.example-user.extraGroups = [ config.users.groups.keys.name ];
}

The following example configures secrets for buildkite, a CI agent the service needs a token and a ssh private key to function:

{ pkgs, config, ... }:
{
  services.buildkite-agents.builder = {
    enable = true;
    tokenPath = config.sops.secrets.buildkite-token.path;
    privateSshKeyPath = config.sops.secrets.buildkite-ssh-key.path;

runtimePackages = [
  pkgs.gnutar
  pkgs.bash
  pkgs.nix
  pkgs.gzip
  pkgs.git
];
  };
  systemd.services.buildkite-agent-builder = {
    serviceConfig.SupplementaryGroups = [ config.users.groups.keys.name ];
  };
  sops.secrets.buildkite-token.owner = config.users.buildkite-agent-builder.name;
  sops.secrets.buildkite-ssh-key.owner = config.users.buildkite-agent-builder.name;
}

Symlinks to other directories

Some services might expect files in certain locations. Using the

path

{
  sops.secrets."home-assistant-secrets.yaml" = {
    owner = "hass";
    path = "/var/lib/hass/secrets.yaml";
  };
}

$ ls -la /var/lib/hass/secrets.yaml
lrwxrwxrwx 1 root root 40 Jul 19 22:36 /var/lib/hass/secrets.yaml -> /run/secrets/home-assistant-secrets.yaml

Different file formats

At the moment we support the following file formats: YAML, JSON, binary

NOTE: At the moment we do not support nested data structures that sops support. This might change in the future:

We support the following yaml:

key: 1

but not:

nested: 
  key: 1

nix-sops allows to specify multiple sops files in different file formats:

{
  imports = [  ];
  # The default sops file used for all secrets can be controlled using `sops.defaultSopsFile`
  sops.defaultSopsFile = ./secrets.yaml;
  # If you use something different from yaml, you can also specify it here:
  #sops.defaultSopsFormat = "yaml";
  sops.secrets.github_token = {
    # The sops file can be also overwritten per secret...
    sopsFile = ./other-secrets.json;
    # ... as well as the format
    format = "json";
  };
}

YAML

Open a new file with sops ending in

.yaml

$ sops secrets.yaml

Than put in the following content:

github_token: 4a6c73f74928a9c4c4bc47379256b72e598e2bd3
# multi-line strings in yaml start with an |
ssh_key: |
  -----BEGIN OPENSSH PRIVATE KEY-----
  b3BlbnNzaC1rZXktdjEAAAAABG5vbmUAAAAEbm9uZQAAAAAAAAABAAAAMwAAAAtzc2gtZW
  QyNTUxOQAAACDENhLwQI4v/Ecv65iCMZ7aZAL+Sdc0Cqyjkd012XwJzQAAAJht4at6beGr
  egAAAAtzc2gtZWQyNTUxOQAAACDENhLwQI4v/Ecv65iCMZ7aZAL+Sdc0Cqyjkd012XwJzQ
  AAAEBizgX7v+VMZeiCtWRjpl95dxqBWUkbrPsUSYF3DGV0rsQ2EvBAji/8Ry/rmIIxntpk
  Av5J1zQKrKOR3TXZfAnNAAAAE2pvZXJnQHR1cmluZ21hY2hpbmUBAg==
  -----END OPENSSH PRIVATE KEY-----

You can include it like this in your

configuration.nix

{
  sops.defaultSopsFile = ./secrets.yaml;
  # yaml is the default 
  #sops.defaultSopsFormat = "yaml";
  sops.secrets.github_token = {
    format = "yaml";
    # can be also set per secret
    sopsFile = ./secrets.yaml;
  };
}

JSON

Open a new file with sops ending in

.json

$ sops secrets.json

Than put in the following content:

{
  "github_token": "4a6c73f74928a9c4c4bc47379256b72e598e2bd3",
  "ssh_key": "-----BEGIN OPENSSH PRIVATE KEY-----\\nb3BlbnNzaC1rZXktdjEAAAAABG5vbmUAAAAEbm9uZQAAAAAAAAABAAAAMwAAAAtzc2gtZW\\nQyNTUxOQAAACDENhLwQI4v/Ecv65iCMZ7aZAL+Sdc0Cqyjkd012XwJzQAAAJht4at6beGr\\negAAAAtzc2gtZWQyNTUxOQAAACDENhLwQI4v/Ecv65iCMZ7aZAL+Sdc0Cqyjkd012XwJzQ\\nAAAEBizgX7v+VMZeiCtWRjpl95dxqBWUkbrPsUSYF3DGV0rsQ2EvBAji/8Ry/rmIIxntpk\\nAv5J1zQKrKOR3TXZfAnNAAAAE2pvZXJnQHR1cmluZ21hY2hpbmUBAg==\\n-----END OPENSSH PRIVATE KEY-----\\n"
}

You can include it like this in your

configuration.nix

{
  sops.defaultSopsFile = ./secrets.json;
  # yaml is the default 
  sops.defaultSopsFormat = "json";
  sops.secrets.github_token = {
    format = "json";
    # can be also set per secret
    sopsFile = ./secrets.json;
  };
}

Binary

Unlike the other two formats for binaries one file correspond to one secret. This format allows to encrypt an arbitrary binary format that can't be put into JSON/YAML files.

To encrypt an binary file use the following command:

$ sops -e /tmp/krb5.keytab > krb5.keytab
$ head krb5.keytab
{
        "data": "ENC[AES256_GCM,data:bIsPHrjrl9wxvKMcQzaAbS3RXCI2h8spw2Ee+KYUTsuousUBU6OMIdyY0wqrX3eh/1BUtl8H9EZciCTW29JfEJKfi3ackGufBH+0wp6vLg7r,iv:TlKiOmQUeH3+NEdDUMImg1XuXg/Tv9L6TmPQrraPlCQ=,tag:dVeVvRM567NszsXKK9pZvg==,type:str]",
        "sops": {
                "kms": null,
                "gcp_kms": null,
                "azure_kv": null,
                "lastmodified": "2020-07-06T06:21:06Z",
                "mac": "ENC[AES256_GCM,data:ISjUzaw/5mNiwypmUrOk2DAZnlkbnhURHmTTYA3705NmRsSyUh1PyQvCuwglmaHscwl4GrsnIz4rglvwx1zYa+UUwanR0+VeBqntHwzSNiWhh7qMAQwdUXmdCNiOyeGy6jcSDsXUeQmyIWH6yibr7hhzoQFkZEB7Wbvcw6Sossk=,iv:UilxNvfHN6WkEvfY8ZIJCWijSSpLk7fqSCWh6n8+7lk=,tag:HUTgyL01qfVTCNWCTBfqXw==,type:str]",
                "pgp": [
                        {

It can be decrypted again like this:

$ sops -d krb5.keytab > /tmp/krb5.keytab

This is how it can be included in your configuration.nix:

{
  sops.secrets.krb5-keytab = {
    format = "binary";
    sopsFile = ./krb5.keytab;
  };
}

Use with GnuPG instead of ssh keys

If you prefer having a separate GnuPG key, sops-nix also comes with a helper tool:

$ nix-shell -p sops-init-gpg-key
$ sops-init-gpg-key --hostname server01 --gpghome /tmp/newkey
You can use the following command to save it to a file:
cat > server01.asc <
In this case you need to make upload the gpg key directory 
/tmp/newkey
 to your server.
If you uploaded it to 
/var/lib/sops
 than your sops configuration will look like this:
{
  # Make sure that `/var/lib/sops` is owned by root and is not world-readable/writable
  sops.gnupg.home = "/var/lib/sops";
  # disable import host ssh keys
  sops.gnupg.sshKeyPaths = [];
}

However be aware that this will also run gnupg on your server including the
gnupg daemon. Gnupg is in general not great software and might break in
hilarious ways. If you experience problems, you are on your own. If you want a
more stable and predictable solution go with ssh keys or one of the KMS services.

Share secrets between different users

Secrets can be shared between different users by creating different files
pointing to the same sops key but with different permissions. In the following
example the 
drone
 secret is exposed as 
/run/secrets/drone-server
 for
drone-server
 and as 
/run/secrets/drone-agent
 for 
drone-agent
{
  sops.secrets.drone-server = {
    owner = config.systemd.services.drone-server.serviceConfig.User;
    key = "drone";
  };
  sops.secrets.drone-agent = {
    owner = config.systemd.services.drone-agent.serviceConfig.User;
    key = "drone";
  };
}

Migrate from pass/krops

If you have used pass before i.e. in krops than you can use
the following one-liner to convert all your secrets to a yaml structure.
$ for i in *.gpg; do echo "$(basename $i .gpg): |\n$(pass $(dirname $i)/$(basename $i .gpg)| sed 's/^/  /')"; done

Copy the output to the editor you have opened with sops.

Realworld Examples

My personal configuration makes extensive usage of sops-nix.
Each host has a secrets directory containing secrets for the host.
You can also checkout nix-community infrastructure repository.

Known limitations

Restarting systemd services

Right now systemd services are not restarted automatically.
We want to implement this in future.

Initrd secrets

sops-nix does not fully support initrd secrets.
This is because 
nixos-rebuild switch
 installs
the bootloader before running sops-nix activation hook.
At the moment it is be possible to run 
nixos-rebuild test
before 
nixos-rebuild switch
 to provision initrd secrets key
before the initrd secrets are built.
In future we hope to extend nixos to allow keys to be
provisioned in the bootloader install phase.