update README

README.md

@@ -1,9 +1,12 @@
-# agenix
+# agenix - [age](https://github.com/FiloSottile/age)-encrypted secrets for NixOS
 
-[age](https://github.com/FiloSottile/age)-encrypted secrets for NixOS.
+`agenix` is a commandline tool for managing secrets encrypted with your existing SSH keys. This project also includes the NixOS module `age` for adding encrypted secrets into the Nix store and decrypting them.
 
-It consists of a NixOS module `age`, and a CLI tool called `agenix`
-used for editing and rekeying the secret files.
+## Problem and solution
+
+All files in the Nix store are readable by any system user, so it is not a suitable place for including cleartext secrets. Many existing tools (like NixOps deployment.keys) deploy secrets separately from `nixos-rebuild`, making deployment, caching, and auditing more difficult. Out-of-band secret management is also less reproducible.
+
+`agenix` solves these issues by using your pre-existing SSH key infrastructure and `age` to encrypt secrets into the Nix store. Secrets are decrypted using an SSH host private key during NixOS system activation.
 
 ## Features
 
@@ -22,7 +25,7 @@ Choose one of the following methods:
 
 First add it to niv:
 
-```console
+```ShellSession
 $ niv add ryantm/agenix
 ```
 
@@ -40,7 +43,7 @@ Then add the following to your configuration.nix in the `imports` list:
 
   As root run:
 
-```console
+```ShellSession
 $ nix-channel --add https://github.com/ryantm/agenix/archive/master.tar.gz agenix
 $ nix-channel --update
 ```
@@ -108,7 +111,7 @@ $ nix-channel --update
 
 You don't need to install it,
 
-```console
+```ShellSession
 nix run github:ryantm/agenix -- --help
 ```
 
@@ -120,13 +123,11 @@ but, if you want to (change the system based on your system):
 }
 ```
 
-
-
 ## Tutorial
 
 1. Make a directory to store secrets and `secrets.nix` file for listing secrets and their public keys:
 
-   ```console
+   ```ShellSession
    $ mkdir secrets
    $ cd secerts
    $ touch secrets.nix
@@ -135,36 +136,41 @@ but, if you want to (change the system based on your system):
    ```nix
    let
      user1 = "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIL0idNvgGiucWgup/mP78zyC23uFjYq0evcWdjGQUaBH";
+     user2 = "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAILI6jSq53F/3hEmSs+oq9L4TwOo1PrDMAgcA1uo1CCV/";
+     users = [ user1 user2 ];
+
      system1 = "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIPJDyIr/FSz1cJdcoW69R+NrWzwGK/+3gJpqD1t8L2zE";
+     system2 = "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIKzxQgondgEYcLpcPdJLrTdNgZ2gznOHCAxMdaceTUT1";
+     systems = [ system1 system2 ];
    in
    {
      "secret1.age".publicKeys = [ user1 system1 ];
-     "secret2.age".publicKeys = [ user1 ];
+     "secret2.age".publicKeys = users ++ systems;
    }
    ```
-3. Edit secret files (assuming your SSH private key is in ~/.ssh/):
-   ```console
+3. Edit secret files (these instructions assume your SSH private key is in ~/.ssh/):
+   ```ShellSession
    $ agenix -e secret1.age
    ```
-4. Add secret to NixOS module config:
+4. Add secret to a NixOS module config:
    ```nix
    age.secrets.secret1.file = ../secrets/secret1.age;
    ```
-5. NixOS rebuild or use your deployment too like usual.
+5. NixOS rebuild or use your deployment tool like usual.
 
 ## Rekeying
 
 If you change the public keys in `secrets.nix`, you should rekey your
 secrets:
 
-```console
+```ShellSession
 $ agenix --rekey
 ```
 
 To rekey a secret, you have to be able to decrypt it. Because of
 randomness in `age`'s encryption algorithms, the files always change
-when rekeyed, even if the identities do not. This eventually could be
-improved upon by reading the identities from the age file.
+when rekeyed, even if the identities do not. (This eventually could be
+improved upon by reading the identities from the age file.)
 
 ## Threat model/Warnings
 
@@ -172,17 +178,15 @@ This project has not be audited by a security professional.
 
 People unfamiliar with `age` might be surprised that secrets are not
 authenticated. This means that every attacker that has write access to
-the repository can modify secrets because public keys are exposed.
+the secret files can modify secrets because public keys are exposed.
 This seems like not a problem on the first glance because changing the
-configuration itself could expose secrets easily. However it is easier
-to review configuration changes rather than random secrets (for
-example 4096-bit rsa keys).  This would be solved by having a message
+configuration itself could expose secrets easily. However, reviewing
+configuration changes is easier than reviewing random secrets (for
+example, 4096-bit rsa keys). This would be solved by having a message
 authentication code (MAC) like other implementations like GPG or
 [sops](https://github.com/Mic92/sops-nix) have, however this was left
 out for simplicity in `age`.
 
 ## Acknowledgements
 
-This project is based off of
-[sops-nix](https://github.com/Mic92/sops-nix) created Mic92. Thank you
-to Mic92 for inspiration and help with making this.
+This project is based off of [sops-nix](https://github.com/Mic92/sops-nix) created Mic92. Thank you to Mic92 for inspiration and advice.