git-secret

Synopsis

Intro

There’s a well known issue with deploying and configuring software on servers: generally you have to store your private data (such as database passwords, application secret-keys, OAuth secret keys, etc) outside of the git repository.

If you do choose to store these secrets unencrypted in your git repo, even if the repository is private, it is a security risk to copy the secrets everywhere you check out your repo.

What are some drawbacks of storing secrets separately from your git repo?

  1. These files are not version controlled. Filenames, locations, and passwords change from time to time, or new information appears, and other information is removed. When secrets are stored separately from your repo, you can not tell for sure which version of the configuration file was used with each commit or deploy.

  2. When building the automated deployment system there will be one extra step: download and place these secret-configuration files where they need to be. This also means you have to maintain extra secure servers where all your secrets are stored.

How does git-secret solve these problems?

  1. git-secret encrypts files and stores them inside your git repository, providing a history of changes for every commit.
  2. git-secret doesn’t require any extra deploy operations other than providing the appropriate private key (to allow decryption), and using git secret reveal to decrypt all the secret files.

What is git-secret?

git-secret is a bash tool to store your private data inside a git repo.

How’s that? Basically, it uses gpg to encrypt files with the public keys of the users that you trust, and which you have specified with git secret tell email@address.id. Then these users can decrypt these files using their personal secret key.

Why deal with all this private/public key stuff? To make it easier to manage access rights. When you want to remove someone’s access, use git secret removeperson email@address.id to delete their public key from your repo’s git-secret keyring, and reencrypt the files. Then they won’t be able to decrypt secrets anymore.

git-secret terminal preview

git-secret - bash tool to store private data inside a git repo.

Usage: Setting up git-secret in a repository

These steps cover the basic process of using git-secret to specify users and files that will interact with git-secret, and to encrypt and decrypt secrets.

  1. Before starting, make sure you have created a gpg RSA key-pair: which are a public key and a secret key pair, identified by your email address and stored with your gpg configuration. Generally this gpg configuration and keys will be stored somewhere in your home directory.

  2. Begin with an existing or new git repository.

  3. Initialize the git-secret repository by running git secret init. The .gitsecret/ folder will be created, with subdirectories keys/ and paths/, .gitsecret/keys/random_seed will be added to .gitignore, and .gitignore will be configured to not ignore .secret files.

Note all the contents of the .gitsecret/ folder should be checked in, /except/ the random_seed file. This also means that of all the files in .gitsecret/, only the random_seed file should be mentioned in your .gitignore file.

  1. Add the first user to the git-secret repo keyring by running git secret tell your@email.id.

  2. Now it’s time to add files you wish to encrypt inside the git-secret repository. This can be done by running git secret add <filenames...> command, which will also (as of 0.2.6) add entries to .gitignore, stopping those files from being be added or committed to the repo unencrypted.

  3. Then run git secret hide to encrypt the files you added with git secret add. The files will be encrypted with the public keys in your git-secret repo’s keyring, each corresponding to a user’s email that you used with tell.

After using git secret hide to encrypt your data, it is safe to commit your changes. NOTE: It’s recommended to add the git secret hide command to your pre-commit hook, so you won’t miss any changes.

  1. Later you can decrypt files with the git secret reveal command, or print their contents to stdout with the git secret cat command. If you used a password on your GPG key (always recommended), it will ask you for your password. And you’re done!

Usage: Adding someone to a repository using git-secret

  1. Get their gpg public-key. You won’t need their secret key. They can export their public key for you using a command like:

gpg --armor --export their@email.com > public_key.txt # armor here makes it ascii

  1. Import this key into your gpg keyring (in ~/.gnupg or similar) by running gpg --import public_key.txt

  2. Now add this person to your secrets repo by running git secret tell their@email.id (this will be the email address associated with their public key)

  3. Now remove the other user’s public key from your personal keyring with gpg --delete-keys their@email.id

  4. The newly added user cannot yet read the encrypted files. Now, re-encrypt the files using git secret reveal; git secret hide -d, and then commit and push the newly encrypted files. (The -d options deletes the unencrypted file after re-encrypting it). Now the newly added user will be able to decrypt the files in the repo using git-secret reveal.

Note that when you first add a user to a git-secret repo, they will not be able to decrypt existing files until another user re-encrypts the files with the new keyring.

If you do not want unexpected keys added, you can configure some server-side security policy with the pre-receive hook.

Using gpg

You can follow a quick gpg tutorial at devdungeon. Here are the most useful commands to get started:

To generate a RSA key-pair, run:

gpg --gen-key

To export your public key, run:

gpg --armor --export your.email@address.com > public-key.gpg

To import the public key of someone else (to share the secret with them for instance), run:

gpg --import public-key.gpg

To make sure you get the original public keys of the indicated persons, be sure to use a secure channel to transfer it, or use a service you trust, preferably one that uses encryption such as Keybase, to retrieve their public key. Otherwise you could grant the wrong person access to your secrets by mistake!

Using git-secret for Continuous Integration / Continuous Deployment (CI/CD)

When using git-secret for CI/CD, you get the benefit that any deployment is necessarily done with the correct configuration, since it is collocated with the changes in your code.

One way of doing it is the following:

  1. create a gpg key for your CI/CD environment. You can chose any name and email address you want: for instance MyApp Example <myapp@example.com> if your app is called MyApp and your CI/CD provider is Example. It is easier not to define a passphrase for that key. However, if defining a passphrase is unavoidable, use a unique passphrase for the private key.
  2. run gpg --armor --export-secret-key myapp@example.com to get your private key value
  3. Create an env var on your CI/CD server GPG_PRIVATE_KEY and assign it the private key value. If a passphrase has been setup for the private key, create another env var on the CI/CD server GPG_PASSPHRASE and assign it the passphrase of the private key.
  4. Then write your Continuous Deployment build script. For instance:
# As the first step: install git-secret,
# see: https://git-secret.io/installation

# Create private key file
echo "$GPG_PRIVATE_KEY" > ./private_key.gpg
# Import private key and avoid the "Inappropriate ioctl for device" error
gpg --batch --yes --pinentry-mode loopback --import private_key.gpg
# Reveal secrets without user interaction and with passphrase. If no passphrase
# is created for the key, remove `-p $GPG_PASSPHRASE`
git secret reveal -p "$GPG_PASSPHRASE"
# carry on with your build script, secret files are available ...

Note: your CI/CD might not allow you to create a multiline value. In that case, you can export it on one line with

gpg --armor --export-secret-key myapp@example.com | tr '\n' ','

You can then create your private key file with:

echo "$GPG_PRIVATE_KEY" | tr ',' '\n' > ./private_key.gpg

Also note: the gpg version on the CI/CD server MUST INTEROPERATE with the one used locally. Otherwise, gpg decryption can fail, which leads to git secret reveal reporting cannot find decrypted version of file error. The best way to ensure this is to use the same version of gnupg on different systems.

Environment Variables and Configuration

You can configure the version of gpg used, or the extension your encrypted files use, to suit your workflow better. To do so, just set the required variable to the value you need. This can be done in your shell environment file or with each git-secret command. See below, or the man page of git-secret for an explanation of the environment variables git-secret uses.

The settings available to be changed are:

  • $SECRETS_VERBOSE - sets the verbose flag to on for all git-secret commands; is identical to using -v on each command that supports it.

  • $SECRETS_GPG_COMMAND - sets the gpg alternatives, defaults to gpg. It can be changed to gpg, gpg2, pgp, /usr/local/gpg or any other value. After doing so rerun the tests to be sure that it won’t break anything. Tested with gpg and gpg2.

  • $SECRETS_GPG_ARMOR - sets the gpg --armor mode. Can be set to 1 to store secrets file as text. By default is 0 and store files as binaries.

  • $SECRETS_EXTENSION - sets the secret files extension, defaults to .secret. It can be changed to any valid file extension.

  • $SECRETS_DIR - sets the directory where git-secret stores its files, defaults to .gitsecret. It can be changed to any valid directory name.

  • $SECRETS_PINENTRY - allows user to specify a setting for gpg’s --pinentry option. See gpg docs for details about gpg’s --pinentry option.

The .gitsecret folder (can be overridden with SECRETS_DIR)

This folder contains information about the files encrypted by git-secret, and about which public/private key sets can access the encrypted data.

You can change the name of this directory using the SECRETS_DIR environment variable.

Use the various git-secret commands to manipulate the files in .gitsecret, you should not change the data in these files directly.

Exactly which files exist in the .gitsecret folder and what their contents are vary slightly across different versions of gpg. Also, some versions of gpg might not work well with keyrings created or modified with newer versions of gpg. Thus it is best to use git-secret with the same version of gpg being used by all users. This can be forced by installing matching versions of gpg and using SECRETS_GPG_COMMAND environment variable.

For example, there is an issue between gpg version 2.1.20 and later versions which can cause problems reading and writing keyring files between systems (this shows up in errors like ‘gpg: skipped packet of type 12 in keybox’).

This is not the only issue it is possible to encounter sharing files between different versions of gpg. Generally you are most likely to encounter issues between gpg versions if you use git-secret tell or git-secret removeperson to modify your repo’s git-secret keyring using a newer version of gpg, and then try to operate on that keyring using an older version of gpg.

The git-secret internal data is separated into two directories:

.gitsecret/paths

This directory currently contains only the file mapping.cfg, which lists all the files your storing encrypted. In other words, the path mappings: what files are tracked to be hidden and revealed.

All the other internal data is stored in the directory:

.gitsecret/keys

This directory contains data used by git-secret and gpg to encrypt files to be accessed by the permitted users.

In particular, this directory contains a gnupg keyring with public keys for the emails used with tell.

This is the keyring used to encrypt files with git-secret-hide.

git-secret-reveal and git-secret-cat, which decrypt secrets, instead use the user’s private keys (which probably reside somewhere like ~/.gnupg/). Note that user’s private keys, needed for decryption, are not in the .gitsecret/keys directory.

Generally speaking, all the files in this directory except random_seed should be checked into your repo. By default, git secret init will add the file .gitsecret/keys/random_seed to your .gitignore file.

Again, you can change the name of this directory using the SECRETS_DIR environment variable.

Command Reference

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