Configure git-crypt

This guide will show you how to configure your agent and your effects to decrypt git-crypt-encrypted files.

git-crypt is a tool that hooks into git to provide per-file encryption. Hercules CI does not decrypt these files before evaluation, so you do not have to worry about accidentally adding secrets to the (system-wide readable) Nix store, or transparently uploading secrets to a binary cache.

hci effect run will add decrypted secrets to the store. This will be resolved in hercules-ci-effects#20. Hercules CI Agent does not experience this problem.


  • You have set up an agent for the account that owns the repository

  • You have added a repository to your Hercules CI installation

  • You are configuring an effect that needs to access decrypted files

Add a private key

With git-crypt, you can give access to the per-repo encryption key via GPG. This means that you can configure your agent(s) with a single private key and then give access to the agents with the git crypt command.

First, generate a key for the agent(s).

$ keyId='Hercules CI Agent <[email protected]>' # replace
$ gpg --quick-generate-key "$keyId"

GPG will ask for a passphrase. If you choose not to use a passphrase, remember to delete the private key at the end of this section.

Add the public and private key to your local secrets.json.

hci secret add default-gpg \
  --string-file privateKey <(gpg --armor --export-secret-key "$keyId") \
  --string-file publicKey <(gpg --armor --export "$keyId")

Copy the new secret to your agent’s secrets.json as well.

Remove the local copy of the private key.

$ gpg --delete-secret-key "$keyId"

Share the key with your agents

You can now share the repository key with your agents.

~/my-repo$ git crypt add-gpg-user "$keyId"

Add decryption to your effect

Add or modify your effect to include the following attributes:

  src = lib.cleanSource ./.;
  inputs = [ effects.git-crypt-hook ];
  preUnpack = ''
    writeGPGKey git-crypt
  secretsMap.git-crypt = "default-gpg";

The src attribute must include:

  • the .git-crypt directory at the root

  • the .gitattributes files

Further reading