Start to document usage.

README.md

@@ -18,8 +18,60 @@ key management APIs such as AWS KMS, GCP KMS, Azure Key Vault.
 - 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.
 
-## Example
+## Usage example
+
+### 1. Install nix-sops
+
+TODO
+
+### 2. Generate a GPG key for yourself
+
+First generate yourself [a GPG key](https://docs.github.com/en/github/authenticating-to-github/generating-a-new-gpg-key) or use nix-sops
+conversion tool to convert an existing ssh key (we only support RSA keys right now):
+
+```
+$ nix-shell -p ssh-to-pgp
+$ ssh-to-pgp -privkey $HOME/.ssh/id_rsa | gpg --import --quiet
+2504791468b153b8a3963cc97ba53d1919c5dfd4
+```
+
+If you get:
+
+```
+ssh-to-pgp: failed to parse private ssh key: ssh: this private key is passphrase protected
+```
+
+then your ssh key is encrypted with your password and you need to create a encrypted copy temporarily:
+
+```
+$ cp $HOME/.ssh/id_rsa /tmp/id_rsa
+$ ssh-keygen -p -N "" -f /tmp/id_rsa
+$ ssh-to-pgp -privkey /tmp/id_rsa | gpg --import --quiet
+```
+
+The hex string printed here is your GPG fingerprint that can be exported to `SOPS_PGP_FP`.
+
+```
+export SOPS_PGP_FP=2504791468b153b8a3963cc97ba53d1919c5dfd4
+```
+
+If you have generated a gnupg key directly you can get your fingerprint like this:
+
+```
+gpg --list-secret-keys --fingerprint
+/tmp/tmp.JA07D1aVRD/pubring.kbx
+-------------------------------
+sec   rsa2048 1970-01-01 [SCE]
+      9F89 C5F6 9A10 281A 8350  14B0 9C3D C61F 7520 87EF
+uid           [ unknown] root <root@localhost>
+```
+
+The fingerprint here is `9F89 C5F6 9A10 281A 8350 14B0 9C3D C61F 7520 87EF`, you
+need to remove the space in-between manually.
+
+### 3. Get a GPG 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
@@ -28,15 +80,92 @@ to store them as gpg keys.
 ```
 $ nix-shell -p ssh-to-gpg
 # One can use ssh-keyscan over the network
-$ ./result/bin/ssh-keyscan -t rsa server01 | ./result/bin/ssh-to-pgp -pubkey - > hosts/server01.gpg
+$ ssh-keyscan -t rsa server01 | ssh-to-pgp -pubkey - > server01.asc
+# server01:22 SSH-2.0-OpenSSH_8.2
+0fd60c8c3b664aceb1796ce02b318df330331003
 # via ssh command:
-$ ssh "cat /etc/ssh/ssh_host_rsa_key.pub" | ./result/bin/ssh-to-gpg -pubkey - > hosts/server01.gpg
-# Or just read them locally
-$ ./result/bin/ssh-to-pgp -pubkey /etc/ssh/ssh_host_rsa_key.pub > hosts/server01.gpg
+$ ssh server01 "cat /etc/ssh/ssh_host_rsa_key.pub" | ssh-to-gpg -pubkey - > hosts/server01.asc
+0fd60c8c3b664aceb1796ce02b318df330331003
+# Or just read them locally (or in a ssh session)
+$ ssh-to-pgp -pubkey /etc/ssh/ssh_host_rsa_key.pub > server01.asc
+0fd60c8c3b664aceb1796ce02b318df330331003
 ```
 
-```
-{}: {
+Also the hex string here is the fingerprint of your server's gpg key that can be exported
+append to `SOPS_PGP_FP`:
 
+```
+export SOPS_PGP_FP=${SOPS_PGP_FP}:2504791468b153b8a3963cc97ba53d1919c5dfd4
+```
+
+If you prefer having a separate gnupg key, sops-nix also comes with a helper tool:
+
+```
+$ 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 <<EOF
+-----BEGIN PGP PUBLIC KEY BLOCK-----
+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+=uvIf
+-----END PGP PUBLIC KEY BLOCK-----
+EOF
+fingerprint: E4CA86768F176AEB6C01554153AF8D7F149613B1
+```
+
+In this case you need to make upload the gpg key directory `/tmp/newkey` to your server.
+
+### 4. Create a sops file
+
+To create a sops file you need to set export `SOPS_PGP_FP` to include both the fingerprint 
+of your personal gpg key (and your colleagues) and your servers:
+
+```
+export SOPS_PGP_FP="2504791468b153b8a3963cc97ba53d1919c5dfd4,2504791468b153b8a3963cc97ba53d1919c5dfd4"
+```
+
+sops-nix automates that with a hook for nix-shell and also takes care of importing all keys, allowing
+public keys to be stored in git:
+
+```
+# shell.nix
+with import <nixpkgs> {};
+mkShell {
+  # imports all files ending in .asc/.gpg and sets $SOPS_PGP_FP.
+  sopsGPGKeyDirs = [ 
+    "./keys/hosts"
+    "./keys/users"
+  ];
+  # Also single files can be imported.
+  #sopsGPGKeys = [ 
+  #  "./keys/users/mic92.asc"
+  #  "./keys/hosts/server01.asc"
+  #];
+  nativeBuildInputs = [
+    (pkgs.callPackage <sops-nix> {}).sops-shell-hook
+    sops
+    ## you may also need gnupg
+    # gnupg
+  ];
 }
 ```
+
+After that you can create a new file with sops
+
+```
+sops secrets.yaml
+```