Using git-secret: A tool to stored encrypted secrets in the repository

In the sixth part of this tutorial series on developing PHP on Docker we will setup git-secret
to store secrets directly in the repository. Everything will be handled through Docker and
added as make targets for a convenient workflow.

FYI:
This tutorial is a precursor to the next a part
Create a CI pipeline for dockerized PHP Apps
because dealing with secrets is an important aspect when setting up a CI system (and later when
deploying to production) – but I feel it’s complex enough to warrant its own article.

All code samples are publicly available in my
Docker PHP Tutorial repository on github.
You find the branch with the final result of this tutorial at
part-6-git-secret-encrypt-repository-docker.

Published parts of the Docker PHP Tutorial

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Introduction

Dealing with secrets (passwords, tokens, key files, etc.) is close to “naming things”
when it comes to hard problems in software engineering. Some things to consider:

security is paramount – but high security often goes hand in hand with high inconvenience
- and if things get too complicated, people look for shortcuts…
in a team, sharing certain secret values is often mandatory
- so now we need to think about secure ways to distribute and update secrets across multiple
  people
concrete secret values often depend on the environment
- inherently tricky to “test” or even “review”, because those values are “by definition”
  different on “your machine” than on “production”

In fact, entire products have been build around dealing with secrets, e.g.
HashiCorp Vault,
AWS Secrets Manager or the
GCP Secret Manager. Introducing those in a project comes
with a certain overhead as it’s yet another service that needs to be integrated and
maintained. Maybe it is the exactly right decision for your use-case – maybe it’s overkill.
By the end of this article you’ll at least be aware of an alternative with a lower barrier to entry.
See also the Pros and cons section in the end for an overview.

Even though it’s
generally not advised to store secrets in a repository,
I’ll propose exactly that in this tutorial:

identify files that contain secret values
make sure they are added to .gitignore
encrypt them via git-secret
commit the encrypted files to the repository

In the end, we will be able to call

make secret-decrypt

to reveal secrets in the codebase, make modifications to them if necessary and then run

make secret-encrypt

to encrypt them again so that they can be committed (and pushed to the remote repository). To
see it in action, check out branch
part-6-git-secret-encrypt-repository-docker
and run the following commands:

# checkout the branch
git checkout part-6-git-secret-encrypt-repository-docker

# build and start the docker setup
make make-init
make docker-build
make docker-up

# "create" the secret key - the file "secret.gpg.example" would usually NOT live in the repo!
cp secret.gpg.example secret.gpg

# initialize gpg
make gpg-init

# ensure that the decrypted secret file does not exist
ls passwords.txt

# decrypt the secret file
make secret-decrypt

# show the content of the secret file
cat passwords.txt

Tooling

We will set up gpg and git-secret in the php base image, so that the tools become available in
all other containers. Please refer to
Docker from scratch for PHP 8.1 Applications in 2022
for an in-depth explanation of the docker images.

Please note, that there is a caveat when using git-secret in a folder that is shared between
the host system and a docker container. I’ll explain that in more detail (including a workaround)
in section
The git-secret directory and the gpg-agent socket.

gpg

gpg is short for The GNU Privacy Guard and is an open source implementation
of the OpenPGP standard. In short, it allows us to create a personal key file pair
(similar to SSH keys) with a private secret key and a public
key that can be shared with other parties whose messages you want to decrypt.

gpg installation

To install it, we can simply run apk add gnupg and thus update
.docker/images/php/base/Dockerfile accordingly

# File: .docker/images/php/base/Dockerfile

RUN apk add --update --no-cache \
        bash \
        gnupg \
        make \
#...

gpg usage

I’ll only cover the strictly necessary gpg commands here. Please refer to
the “Using GPG” section in the git-secret docu
and/or How to generate PGP keys with GPG
for further information.

Create GPG key pair

We need gpg to create the gpg key pair via

name="Pascal Landau"
email="[email protected]"
gpg --batch --gen-key <<EOF
Key-Type: 1
Key-Length: 2048
Subkey-Type: 1
Subkey-Length: 2048
Name-Real: $name
Name-Email: $email
Expire-Date: 0
%no-protection
EOF

The %no-protection will create a key without password, see
also this gist to “Creating gpg keys non-interactively”.

Output:

$ name="Pascal Landau"
$ email="[email protected]"
$ gpg --batch --gen-key <<EOF
> Key-Type: 1
> Key-Length: 2048
> Subkey-Type: 1
> Subkey-Length: 2048
> Name-Real: $name
> Name-Email: $email
> Expire-Date: 0
> %no-protection
> EOF
gpg: key E1E734E00B611C26 marked as ultimately trusted
gpg: revocation certificate stored as '/root/.gnupg/opengpg-revocs.d/74082D81525723F5BF5B2099E1E734E00B611C26.rev'

You could also run gpg --gen-key without the --batch flag to be guided interactively through the
process.

Export, list and import private GPG keys

The private key can be exported via

email="[email protected]"
path="secret.gpg"
gpg --output "$path" --armor --export-secret-key "$email"

This secret key must never be shared!

It looks like this:

All secret keys can be listed via

gpg --list-secret-keys

Output:

$ gpg --list-secret-keys
/root/.gnupg/pubring.kbx
------------------------
sec   rsa2048 2022-03-27 [SCEA]
      74082D81525723F5BF5B2099E1E734E00B611C26
uid           [ultimate] Pascal Landau <[email protected]>
ssb   rsa2048 2022-03-27 [SEA]

You can import the private key via

path="secret.gpg"
gpg --import "$path"

and get the following output:

$ path="secret.gpg"
$ gpg --import "$path"
gpg: key E1E734E00B611C26: "Pascal Landau <[email protected]>" not changed
gpg: key E1E734E00B611C26: secret key imported
gpg: Total number processed: 1
gpg:              unchanged: 1
gpg:       secret keys read: 1
gpg:  secret keys unchanged: 1

Caution: If the secret key requires a password, you would now be prompted for it. We can
circumvent the prompt by using --batch --yes --pinentry-mode loopback:

path="secret.gpg"
gpg --import --batch --yes --pinentry-mode loopback "$path"

See also Using Command-Line Passphrase Input for GPG.
In doing so, we don’t need to provide the password just yet – but we must pass it later when we
attempt to decrypt files.

Export, list and import public GPG keys

The public key can be exported to public.gpg via

email="[email protected]"
path="public.gpg"
gpg --armor --export "$email" > "$path"

It looks like this:

List all public keys via

gpg --list-keys

Output:

$ gpg --list-keys
/root/.gnupg/pubring.kbx
------------------------
pub   rsa2048 2022-03-27 [SCEA]
      74082D81525723F5BF5B2099E1E734E00B611C26
uid           [ultimate] Pascal Landau <[email protected]>
sub   rsa2048 2022-03-27 [SEA]

The public key can be imported in the same way as private keys via

path="public.gpg"
gpg --import "$path"

Example:

$ gpg --import /var/www/app/public.gpg
gpg: key E1E734E00B611C26: "Pascal Landau <[email protected]>" not changed
gpg: Total number processed: 1
gpg:              unchanged: 1

git-secret

The official website of git-secret is already doing a great job of
introducing the tool. In short, it allows us to declare certain files as “secrets” and encrypt
them via gpg – using the keys of all trusted parties. The encrypted file can then by stored
safely directly in the git repository and decrypted if required.

In this tutorial I’m using git-secret v0.4.0

$ git secret --version
0.4.0

git-secret installation

The installation instructions for Alpine read as
follows:

sh -c "echo 'https://gitsecret.jfrog.io/artifactory/git-secret-apk/all/main'" >> /etc/apk/repositories
wget -O /etc/apk/keys/git-secret-apk.rsa.pub 'https://gitsecret.jfrog.io/artifactory/api/security/keypair/public/repositories/git-secret-apk'
apk add --update --no-cache git-secret

We update the .docker/images/php/base/Dockerfile accordingly:

# File: .docker/images/php/base/Dockerfile

# install git-secret
# @see https://git-secret.io/installation#alpine
ADD https://gitsecret.jfrog.io/artifactory/api/security/keypair/public/repositories/git-secret-apk /etc/apk/keys/git-secret-apk.rsa.pub

RUN echo "https://gitsecret.jfrog.io/artifactory/git-secret-apk/all/main" >> /etc/apk/repositories  && \
    apk add --update --no-cache \
        bash \
        git-secret \
        gnupg \
        make \
#...

git-secret usage

Initialize git-secret

git-secret is initialized via the following command run in the root of the git repository

git secret init

$ git secret init
git-secret: init created: '/var/www/app/.gitsecret/'

We only need to do this once, because we’ll commit the folder to git later. It contains the
following files:

$ git status | grep ".gitsecret"
        new file:   .gitsecret/keys/pubring.kbx
        new file:   .gitsecret/keys/pubring.kbx~
        new file:   .gitsecret/keys/trustdb.gpg
        new file:   .gitsecret/paths/mapping.cfg

The pubring.kbx~ file (with the trailing tilde ~) is only a temporary file and can safely be
git-ignored. See also
Can’t find any docs about keyring.kbx~ file.

The `git-secret` directory and the `gpg-agent` socket

To use git-secret in a directory that is shared between the host system and docker, we need to
also run the following commands:

tee .gitsecret/keys/S.gpg-agent <<EOF
%Assuan%
socket=/tmp/S.gpg-agent
EOF

tee .gitsecret/keys/S.gpg-agent.ssh <<EOF
%Assuan%
socket=/tmp/S.gpg-agent.ssh
EOF

tee .gitsecret/keys/gpg-agent.conf <<EOF
extra-socket /tmp/S.gpg-agent.extra
browser-socket /tmp/S.gpg-agent.browser
EOF

This is necessary because there is an issue when git-secret is used in a setup where the
codebase is shared between the host system and a docker container.
I’ve explained the details in the Github issue
“gpg: can’t connect to the agent: IPC connect call failed” error in docker alpine on shared volume.

In short:

gpg uses a gpg-agent to perform its tasks and the two tools communicate through sockets
that are created in the --home-directory of the gpg-agent
the agent is started implicitly through a gpg command used by git-secret, using the
.gitsecret/keys directories as a --home-directory
because the location of the --home-directory is shared with the host system, the socket
creation fails (potentially only an issue for Docker Desktop, see the related discussion in
Github issue Support for sharing unix sockets)

The corresponding error messages are

gpg: can't connect to the agent: IPC connect call failed

gpg-agent: error binding socket to '/var/www/app/.gitsecret/keys/S.gpg-agent': I/O error

The workaround for this problem can be found in
this thread: Configure gpg to use different
locations for the sockets by
placing additional gpg configuration files in the .gitsecret/keys directory:

S.gpg-agent

%Assuan%
socket=/tmp/S.gpg-agent

S.gpg-agent.ssh

%Assuan%
socket=/tmp/S.gpg-agent.ssh

gpg-agent.conf

extra-socket /tmp/S.gpg-agent.extra
browser-socket /tmp/S.gpg-agent.browser

Adding, listing and removing users

To add a new user, you must first import its public gpg key. Then
run:

email="[email protected]"
git secret tell "$email"

In this case, the user [email protected] will now be able to decrypt the secrets.

To show the users run

git secret whoknows

$ git secret whoknows
[email protected]

To remove a user, run

email="[email protected]"
git secret killperson "$email"

FYI: This command was renamed to removeperson in git-secret >= 0.5.0

$ git secret killperson [email protected]
git-secret: removed keys.
git-secret: now [[email protected]] do not have an access to the repository.
git-secret: make sure to hide the existing secrets again.

User [email protected] will no longer be able to decrypt the secrets.

Caution: The secrets need to be re-encrypted after removing a user!

Reminder: Rotate the encrypted secrets

Please be aware that not only your secrets are stored in git, but who had access as well. I.e.
even if you remove a user and re-encrypt the secrets, that user would still be able to decrypt
the secrets of a previous commit (when the user was still added). In consequence, you need
to rotate the encrypted secrets themselves as well after removing a user.

But isn’t that a great flaw in the system, making it a bad idea to use git-secret in general?

In my opinion: No.

If the removed user had access to the secrets at any point in time (no
matter where they have been stored), he could very well have just created a local copy or simply
“written them down”. In terms of security there is really no “added downside” due to git-secret.
It just makes it very clear that you must rotate the secrets ¯\_(ツ)_/¯

Adding, listing and removing files for encryption

Run git secret add [filenames...] for files you want to encrypt. Example:

git secret add .env

If .env is not added in .gitignore, git-secret will display a warning and add it
automatically.

git-secret: these files are not in .gitignore: .env
git-secret: auto adding them to .env
git-secret: 1 item(s) added.

Otherwise, the file is added with no warning.

$ git secret add .env
git-secret: 1 item(s) added.

You only need to add files once. They are then stored in .gitsecret/paths/mapping.cfg:

$ cat .gitsecret/paths/mapping.cfg
.env:505070fc20233cb426eac6a3414399d0f466710c993198b1088e897fdfbbb2d5

You can also show the added files via

git secret list

$ git secret list
.env

Caution: The files are not yet encrypted!

If you want to remove a file from being encrypted, run

git secret remove .env

Output

$ git secret remove .env
git-secret: removed from index.
git-secret: ensure that files: [.env] are now not ignored.

Encrypt files

To actually encrypt the files, run:

git secret hide

Output:

$ git secret hide
git-secret: done. 1 of 1 files are hidden.

The encrypted (binary) file is stored at $filename.secret, i.e. .env.secret in this case:

$ cat .env.secret
�☺♀♥�H~�B�Ӯ☺�"��▼♂F�►���l�Cs��S�@MHWs��e������{♣♫↕↓�L� ↕s�1�J$◄♥�;���ǆ֕�Za�����\u�ٲ& ¶��V�► ���6��
;<�d:��}ҨD%.�;��&��G����vWW�]>���߶��▲;D�+Rs�S→�Y!&J��۪8���ٔF��→f����*��$♠���&RC�8▼♂�☻z h��Z0M�T>

The encrypted files are de-cryptable for all users that have been added via git secret tell.
That also means that you need to run this command again whenever a new user is added.

Decrypting files

You can decrypt files via

git secret reveal

Output:

$ git secret reveal
File '/var/www/app/.env' exists. Overwrite? (y/N) y
git-secret: done. 1 of 1 files are revealed.

the files are decrypted and will overwrite the current, unencrypted files (if they already exist)
- use the -f option to force the overwrite and run non-interactively
if you only want to check the content of an encrypted file, you can use
git secret cat $filename (e.g. git secret cat .env)

In case the secret gpg key is password protected, you must pass the password
via the -p option. E.g. for password 123456

git secret reveal -p 123456

Show changes between encrypted and decrypted files

One problem that comes with encrypted files: You can’t review them during a code review in a
remote tool. So in order to understand what changes have been made, it is helpful to
show the changes between the encrypted and the decrypted files. This can be done via

git secret changes

Output:

$ echo "foo" >> .env
$ git secret changes
git-secret: changes in /var/www/app/.env:
--- /dev/fd/63
+++ /var/www/app/.env
@@ -34,3 +34,4 @@
 MAIL_ENCRYPTION=null
 MAIL_FROM_ADDRESS=null
 MAIL_FROM_NAME="${APP_NAME}"
+foo

Note the +foo at the bottom of the output. It was added in the first line via
echo "foo"> >> .env.

Makefile adjustments

Since I won’t be able to remember all the commands for git-secret and gpg, I’ve added them to
the Makefile at .make/01-00-application-setup.mk:

# File: .make/01-00-application-setup.mk

#...

# gpg

DEFAULT_SECRET_GPG_KEY?=secret.gpg
DEFAULT_PUBLIC_GPG_KEYS?=.dev/gpg-keys/*

.PHONY: gpg
gpg: ## Run gpg commands. Specify the command e.g. via ARGS="--list-keys"
    $(EXECUTE_IN_APPLICATION_CONTAINER) gpg $(ARGS)

.PHONY: gpg-export-public-key
gpg-export-public-key: ## Export a gpg public key e.g. via EMAIL="[email protected]" PATH=".dev/gpg-keys/john-public.gpg"
    @$(if $(PATH),,$(error PATH is undefined))
    @$(if $(EMAIL),,$(error EMAIL is undefined))
    "$(MAKE)" -s gpg ARGS="gpg --armor --export $(EMAIL) > $(PATH)"

.PHONY: gpg-export-private-key
gpg-export-private-key: ## Export a gpg private key e.g. via EMAIL="[email protected]" PATH="secret.gpg"
    @$(if $(PATH),,$(error PATH is undefined))
    @$(if $(EMAIL),,$(error EMAIL is undefined))
    "$(MAKE)" -s gpg ARGS="--output $(PATH) --armor --export-secret-key $(EMAIL)"

.PHONY: gpg-import
gpg-import: ## Import a gpg key file e.g. via GPG_KEY_FILES="/path/to/file /path/to/file2"
    @$(if $(GPG_KEY_FILES),,$(error GPG_KEY_FILES is undefined))
    "$(MAKE)" -s gpg ARGS="--import --batch --yes --pinentry-mode loopback $(GPG_KEY_FILES)"

.PHONY: gpg-import-default-secret-key
gpg-import-default-secret-key: ## Import the default secret key
    "$(MAKE)" -s gpg-import GPG_KEY_FILES="$(DEFAULT_SECRET_GPG_KEY)"

.PHONY: gpg-import-default-public-keys
gpg-import-default-public-keys: ## Import the default public keys
    "$(MAKE)" -s gpg-import GPG_KEY_FILES="$(DEFAULT_PUBLIC_GPG_KEYS)" 

.PHONY: gpg-init
gpg-init: gpg-import-default-secret-key gpg-import-default-public-keys ## Initialize gpg in the container, i.e. import all public and private keys

# git-secret

.PHONY: git-secret
git-secret: ## Run git-secret commands. Specify the command e.g. via ARGS="hide"
    $(EXECUTE_IN_APPLICATION_CONTAINER) git-secret $(ARGS)

.PHONY: secret-init
secret-init: ## Initialize git-secret in the repository via `git-secret init`
    "$(MAKE)" -s git-secret ARGS="init"

.PHONY: secret-init-gpg-socket-config
secret-init-gpg-socket-config: ## Initialize the config files to change the gpg socket locations
    echo "%Assuan%" > .gitsecret/keys/S.gpg-agent
    echo "socket=/tmp/S.gpg-agent" >> .gitsecret/keys/S.gpg-agent
    echo "%Assuan%" > .gitsecret/keys/S.gpg-agent.ssh
    echo "socket=/tmp/S.gpg-agent.ssh" >> .gitsecret/keys/S.gpg-agent.ssh
    echo "extra-socket /tmp/S.gpg-agent.extra" > .gitsecret/keys/gpg-agent.conf
    echo "browser-socket /tmp/S.gpg-agent.browser" >> .gitsecret/keys/gpg-agent.conf

.PHONY: secret-encrypt
secret-encrypt: ## Decrypt secret files via `git-secret hide`
    "$(MAKE)" -s git-secret ARGS="hide"

.PHONY: secret-decrypt
secret-decrypt: ## Decrypt secret files via `git-secret reveal -f`
    "$(MAKE)" -s git-secret ARGS="reveal -f" 

.PHONY: secret-decrypt-with-password
secret-decrypt-with-password: ## Decrypt secret files using a password for gpg via `git-secret reveal -f -p $(GPG_PASSWORD)`
    @$(if $(GPG_PASSWORD),,$(error GPG_PASSWORD is undefined))
    "$(MAKE)" -s git-secret ARGS="reveal -f -p $(GPG_PASSWORD)" 

.PHONY: secret-add
secret-add: ## Add a file to git secret via `git-secret add $FILE`
    @$(if $(FILE),,$(error FILE is undefined))
    "$(MAKE)" -s git-secret ARGS="add $(FILE)"

.PHONY: secret-cat
secret-cat: ## Show the contents of file to git secret via `git-secret cat $FILE`
    @$(if $(FILE),,$(error FILE is undefined))
    "$(MAKE)" -s git-secret ARGS="cat $(FILE)"

.PHONY: secret-list
secret-list: ## List all files added to git secret `git-secret list`
    "$(MAKE)" -s git-secret ARGS="list"

.PHONY: secret-remove
secret-remove: ## Remove a file from git secret via `git-secret remove $FILE`
    @$(if $(FILE),,$(error FILE is undefined))
    "$(MAKE)" -s git-secret ARGS="remove $(FILE)"

.PHONY: secret-add-user
secret-add-user: ## Remove a user from git secret via `git-secret tell $EMAIL`
    @$(if $(EMAIL),,$(error EMAIL is undefined))
    "$(MAKE)" -s git-secret ARGS="tell $(EMAIL)"

.PHONY: secret-show-users
secret-show-users: ## Show all users that have access to git secret via `git-secret whoknows`
    "$(MAKE)" -s git-secret ARGS="whoknows"

.PHONY: secret-remove-user
secret-remove-user: ## Remove a user from git secret via `git-secret killperson $EMAIL`
    @$(if $(EMAIL),,$(error EMAIL is undefined))
    "$(MAKE)" -s git-secret ARGS="killperson $(EMAIL)"

.PHONY: secret-diff
secret-diff: ## Show the diff between the content of encrypted and decrypted files via `git-secret changes`
    "$(MAKE)" -s git-secret ARGS="changes"

Workflow

Working with git-secret is pretty straight forward:

initialize git-secret
add all users
add all secret files and make sure they are ignored via .gitignore
encrypt the files
commit the encrypted files like “any other file”
if any changes were made by other team members to the files:
- => decrypt to get the most up-to-date ones
if any modifications are required from your side:
- => make the changes to the decrypted files and then re-encrypt them again

But: The devil is in the details. The Process challenges section explains
some of the pitfalls that we have encountered and the Scenarios section gives some
concrete examples for common scenarios.

Process challenges

From a process perspective we’ve encountered some challenges that I’d like to mention – including
how we deal with them.

Updating secrets

When updating secrets you must ensure to always decrypt the files first in order to avoid
using “stale” files that you might still have locally. I usually check out the latest main
branch and run git secret reveal to have the most up-to-date versions of the secret files. You
could also use a post-merge git hook to do
this automatically, but I personally don’t want to risk overwriting my local secret files by
accident.

Code reviews and merge conflicts

Since the encrypted files cannot be diffed meaningfully, the code reviews become more difficult
when secrets are involved. We use Gitlab for reviews and I usually first check the diff of
the .gitsecret/paths/mapping.cfg file to see “which files have changed” directly in the UI.

In addition, I will

checkout the main branch
decrypt the secrets via git secret reveal -f
checkout the feature-branch
run git secret changes to see the differences between the decrypted files from main and the
encrypted files from feature-branch

Things get even more complicated when multiple team members need to modify secret files at the same
time on different branches, as the encrypted files cannot be compared – i.e. git cannot be smart
about delta updates.
The only way around this is coordinating the pull requests, i.e. merge the first, update the
secrets of the second and then merge the second.

Fortunately, this has only happened very rarely so far.

Local `git-secret` and `gpg` setup

Currently, all developers in our team have git-secret installed locally (instead of using it
through docker) and use their own gpg keys.

This means more onboarding overhead, because

a new dev must
- install git-secret locally (*)
- install and setup gpg locally (*)
- create a gpg key pair
the public key must be added by every other team member (*)
the user of the key must be added via git secret tell
the secrets must be re-encrypted

And for offboarding

the public key must be removed by every other team member (*)
the user of the key must be removed via git secret killperson
the secrets must be re-encrypted

Plus, we need to ensure that the git-secret and gpg versions are kept up-to-date for everyone to
not run into any compatibility issues.

As an alternative, I’m currently leaning more towards handling everything through docker (as
presented in this tutorial). All steps marked with (*) are then obsolete, i.e. there is no need
to setup git-secret and gpg locally.

But the approach also comes with some downsides, because

the secret key and all public keys have to be imported every time the container is started
each dev needs to put his private gpg key “in the codebase” (ignored by .gitignore) so it
can be shared with docker and imported by gpg (in docker). The alternative would be using
a single secret key that is shared within the team – which feels very wrong 😛

To make this a little more convenient, we put the public gpg keys of every dev in the
repository under .dev/gpg-keys/ and the private key has to be named secret.gpg and put
in the root of the codebase.

In this setup, secret.gpg must also be added to the.gitignore file.

# File: .gitignore
#...
vendor/
secret.gpg

The import can now be be simplified with make targets:

# gpg

DEFAULT_SECRET_GPG_KEY?=secret.gpg
DEFAULT_PUBLIC_GPG_KEYS?=.dev/gpg-keys/*

.PHONY: gpg
gpg: ## Run gpg commands. Specify the command e.g. via ARGS="--list-keys"
    $(EXECUTE_IN_APPLICATION_CONTAINER) gpg $(ARGS)

.PHONY: gpg-import
gpg-import: ## Import a gpg key file e.g. via GPG_KEY_FILES="/path/to/file /path/to/file2"
    @$(if $(GPG_KEY_FILES),,$(error GPG_KEY_FILES is undefined))
    "$(MAKE)" -s gpg ARGS="--import --batch --yes --pinentry-mode loopback $(GPG_KEY_FILES)"

.PHONY: gpg-import-default-secret-key
gpg-import-default-secret-key: ## Import the default secret key
    "$(MAKE)" -s gpg-import GPG_KEY_FILES="$(DEFAULT_SECRET_GPG_KEY)"

.PHONY: gpg-import-default-public-keys
gpg-import-default-public-keys: ## Import the default public keys
    "$(MAKE)" -s gpg-import GPG_KEY_FILES="$(DEFAULT_PUBLIC_GPG_KEYS)" 

.PHONY: gpg-init
gpg-init: gpg-import-default-secret-key gpg-import-default-public-keys ## Initialize gpg in the container, i.e. import all public and private keys

“Everything” can now be handled via

make gpg-init

that needs to be run one single time after a container has been started.

Scenarios

The scenarios assume the following preconditions:

You have checked out branch part-6-git-secret-encrypt-repository-docker
```
git checkout part-6-git-secret-encrypt-repository-docker
```
and no running docker containers
```
make docker-down
```
You have deleted the existing git-secret folder, the keys in .dev/gpg-keys, the
secret.gpg key and the passwords.* files
```
rm -rf .gitsecret/ .dev/gpg-keys/* secret.gpg passwords.*
```

Initial setup of `gpg` keys

Unfortunately, I didn’t find a way to create and export gpg keys through make and docker. You
need to either run the commands interactively OR pass a string with newlines to it. Both things are
horribly complicated with make and docker. Thus, you need to log into the application
container and run the commands in there directly. Not great – but this needs to be done only
once when a new developer is onboarded anyways.

FYI: I usually log into containers via
Easy container access via din .bashrc helper.

The secret key is exported to secret.gpg and the public key to .dev/gpg-keys/alice-public.gpg.

# start the docker setup
make docker-up

# log into the container ('winpty' is only required on Windows)
winpty docker exec -ti dofroscra_local-application-1 bash

# export key pair
name="Alice Doe"
email="[email protected]"
gpg --batch --gen-key <<EOF
Key-Type: 1
Key-Length: 2048
Subkey-Type: 1
Subkey-Length: 2048
Name-Real: $name
Name-Email: $email
Expire-Date: 0
%no-protection
EOF

# export the private key
gpg --output secret.gpg --armor --export-secret-key $email

# export the public key
gpg --armor --export $email > .dev/gpg-keys/alice-public.gpg

$ make docker-up
ENV=local TAG=latest DOCKER_REGISTRY=docker.io DOCKER_NAMESPACE=dofroscra APP_USER_NAME=application APP_GROUP_NAME=application docker compose -p dofroscra_local --env-file ./.docker/.env -f ./.docker/docker-compose/docker-compose.yml -f ./.docker/docker-compose/docker-compose.local.yml up -d
Container dofroscra_local-application-1  Created
...
Container dofroscra_local-application-1  Started
$ docker ps
CONTAINER ID   IMAGE                                COMMAND                  CREATED          STATUS          PORTS                NAMES
...
95f740607586   dofroscra/application-local:latest   "/usr/sbin/sshd -D"      21 minutes ago   Up 21 minutes   0.0.0.0:2222->22/tcp dofroscra_local-application-1

$ winpty docker exec -ti dofroscra_local-application-1 bash
root:/var/www/app# name="Alice Doe"
root:/var/www/app# email="[email protected]"
gpg --batch --gen-key <<EOF
Key-Type: 1
Key-Length: 2048
Subkey-Type: 1
Subkey-Length: 2048
Name-Real: $name
Name-Email: $email
Expire-Date: 0
%no-protection
EOF
root:/var/www/app# gpg --batch --gen-key <<EOF
> Key-Type: 1
> Key-Length: 2048
> Subkey-Type: 1
> Subkey-Length: 2048
> Name-Real: $name
> Name-Email: $email
> Expire-Date: 0
> %no-protection
> EOF
gpg: directory '/root/.gnupg' created
gpg: keybox '/root/.gnupg/pubring.kbx' created
gpg: /root/.gnupg/trustdb.gpg: trustdb created
gpg: key BBBE654440E720C1 marked as ultimately trusted
gpg: directory '/root/.gnupg/openpgp-revocs.d' created
gpg: revocation certificate stored as '/root/.gnupg/openpgp-revocs.d/225C736E0E70AC222C072B70BBBE654440E720C1.rev'

root:/var/www/app# gpg --output secret.gpg --armor --export-secret-key $email
root:/var/www/app# head secret.gpg
-----BEGIN PGP PRIVATE KEY BLOCK-----
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root:/var/www/app# gpg --armor --export $email > .dev/gpg-keys/alice-public.gpg
root:/var/www/app# head .dev/gpg-keys/alice-public.gpg
-----BEGIN PGP PUBLIC KEY BLOCK-----

mQENBGJD+bwBCADBGKySV5PINc5MmQB3PNvCG7Oa1VMBO8XJdivIOSw7ykv55PRP
3g3R+ERd1Ss5gd5KAxLc1tt6PHGSPTypUJjCng2plwD8Jy5A/cC6o2x8yubOslLa
x1EC9fpcxUYUNXZavtEr+ylOaTaRz6qwSabsAgkg2NZ0ey/QKmFOZvhL8NlK9lTI
GgZPTiqPCsr7hiNg0WRbT5h8nTmfpl/DdTgwfPsDn5Hn0TEMa79WsrPnnq16jsq0
Uusuw3tOmdSdYnT8j7m1cpgcSj0hRF1eh4GVE0o62GqeLTWW9mfpcuv7n6mWaCB8
DCH6H238gwUriq/aboegcuBktlvSY21q/MIXABEBAAG0HUFsaWNlIERvZSA8YWxp
Y2VAZXhhbXBsZS5jb20+iQFOBBMBCgA4FiEEIlxzbg5wrCIsBytwu75lREDnIMEF
AmJD+bwCGy8FCwkIBwIGFQoJCAsCBBYCAwECHgECF4AACgkQu75lREDnIMEN4Af+

That’s it. We now have a new secret and private key for [email protected] and have exported it to
secret.gpg resp. .dev/gpg-keys/alice-public.gpg (and thus shared it with the host system).
The remaining commands can now be run outside of the application container directly on the
host system.

Initial setup of `git-secret`

Let’s say we want to introduce git-secret “from scratch” to a new codebase. Then you would run
the following commands:

Initialize git-secret

make secret-init

$ make secret-init
"C:/Program Files/Git/mingw64/bin/make" -s git-secret ARGS="init";
git-secret: init created: '/var/www/app/.gitsecret/'

Apply the gpg fix for shared directories

See The git-secret directory and the gpg-agent socket.

$ make secret-init-gpg-socket-config

$ make secret-init-gpg-socket-config
echo "%Assuan%" > .gitsecret/keys/S.gpg-agent
echo "socket=/tmp/S.gpg-agent" >> .gitsecret/keys/S.gpg-agent
echo "%Assuan%" > .gitsecret/keys/S.gpg-agent.ssh
echo "socket=/tmp/S.gpg-agent.ssh" >> .gitsecret/keys/S.gpg-agent.ssh
echo "extra-socket /tmp/S.gpg-agent.extra" > .gitsecret/keys/gpg-agent.conf
echo "browser-socket /tmp/S.gpg-agent.browser" >> .gitsecret/keys/gpg-agent.conf

Initialize `gpg` after container startup

After restarting the containers, we need to initialize gpg, i.e. import all public keys from
.dev/gpg-keys/* and the private key from secret.gpg. Otherwise we will not be able to en-
and decrypt the files.

make gpg-init

$ make gpg-init
"C:/Program Files/Git/mingw64/bin/make" -s gpg-import GPG_KEY_FILES="secret.gpg"
gpg: directory '/home/application/.gnupg' created
gpg: keybox '/home/application/.gnupg/pubring.kbx' created
gpg: /home/application/.gnupg/trustdb.gpg: trustdb created
gpg: key BBBE654440E720C1: public key "Alice Doe <[email protected]>" imported
gpg: key BBBE654440E720C1: secret key imported
gpg: Total number processed: 1
gpg:               imported: 1
gpg:       secret keys read: 1
gpg:   secret keys imported: 1
"C:/Program Files/Git/mingw64/bin/make" -s gpg-import GPG_KEY_FILES=".dev/gpg-keys/*"
gpg: key BBBE654440E720C1: "Alice Doe <[email protected]>" not changed
gpg: Total number processed: 1
gpg:              unchanged: 1

Adding (new) team members

Let’s start by adding our own user to git-secret

make secret-add-user EMAIL="[email protected]"

$ make secret-add-user EMAIL="[email protected]"
"C:/Program Files/Git/mingw64/bin/make" -s git-secret ARGS="tell [email protected]"
git-secret: done. [email protected] added as user(s) who know the secret.

And verify that it worked via

make secret-show-users

$ make secret-show-users
"C:/Program Files/Git/mingw64/bin/make" -s git-secret ARGS="whoknows"
[email protected]

Adding and encrypting files

Let’s add a new encrypted file secret_password.txt.

Create the file

echo "my_new_secret_password" > secret_password.txt

Add it to .gitignore

echo "secret_password.txt" >> .gitignore

Add it to git-secret

make secret-add FILE="secret_password.txt"

$ make secret-add FILE="secret_password.txt"
"C:/Program Files/Git/mingw64/bin/make" -s git-secret ARGS="add secret_password.txt"
git-secret: 1 item(s) added.

Encrypt all files

make secret-encrypt

$ make secret-encrypt
"C:/Program Files/Git/mingw64/bin/make" -s git-secret ARGS="hide"
git-secret: done. 1 of 1 files are hidden.

$ ls secret_password.txt.secret
secret_password.txt.secret

Decrypt files

Let’s first remove the “plain” secret_password.txt file

rm secret_password.txt

$ rm secret_password.txt

$ ls secret_password.txt
ls: cannot access 'secret_password.txt': No such file or directory

and then decrypt the encrypted one.

make secret-decrypt

$ make secret-decrypt
"C:/Program Files/Git/mingw64/bin/make" -s git-secret ARGS="reveal -f"
git-secret: done. 1 of 1 files are revealed.

$ cat secret_password.txt
my_new_secret_password

Caution: If the secret gpg key is password protected (e.g. 123456), run

make secret-decrypt-with-password GPG_PASSWORD=123456

You could also add the GPG_PASSWORD variable to the
.make/.env
file as a local default value so that you wouldn’t have to specify the value every time and
could then simply run

make secret-decrypt-with-password

without passing GPG_PASSWORD

Removing files

Remove the secret_password.txt file we added previously:

make secret-remove FILE="secret_password.txt"

$ make secret-remove FILE="secret_password.txt"
"C:/Program Files/Git/mingw64/bin/make" -s git-secret ARGS="remove secret_password.txt"
git-secret: removed from index.
git-secret: ensure that files: [secret_password.txt] are now not ignored.

Caution: this will neither remove the secret_password.txt file nor
the secret_password.txt.secret file automatically”

$ ls -l | grep secret_password.txt
-rw-r--r-- 1 Pascal 197121     19 Mar 31 14:03 secret_password.txt
-rw-r--r-- 1 Pascal 197121    358 Mar 31 14:02 secret_password.txt.secret

But even though the encrypted secret_password.txt.secret file still exists, it will not be
decrypted:

$ make secret-decrypt
"C:/Program Files/Git/mingw64/bin/make" -s git-secret ARGS="reveal -f"
git-secret: done. 0 of 0 files are revealed.

Removing team members

Removing a team member can be done via

make secret-remove-user EMAIL="[email protected]"

$ make secret-remove-user EMAIL="[email protected]"
"C:/Program Files/Git/mingw64/bin/make" -s git-secret ARGS="killperson [email protected]"
git-secret: removed keys.
git-secret: now [[email protected]] do not have an access to the repository.
git-secret: make sure to hide the existing secrets again.

If there are any users left, we must make sure to re-encrypt the secrets via

make secret-encrypt

Otherwise (if no more users are left) git-secret would simply error out

$ make secret-decrypt
"C:/Program Files/Git/mingw64/bin/make" -s git-secret ARGS="reveal -f"
git-secret: abort: no public keys for users found. run 'git secret tell [email protected]'.
make[1]: *** [.make/01-00-application-setup.mk:57: git-secret] Error 1
make: *** [.make/01-00-application-setup.mk:69: secret-decrypt] Error 2

Caution: Please keep in mind to
rotate the secrets themselves as well!

Pros and cons

Pro

very low barrier to entry:
- no third party service required
- easy to integrate in existing codebases, because the secrets are located directly in
  the codebase
- everything can be handled through docker (no additional local software necessary)
once set up, it is very easy/convenient to use and can be integrated in a team workflow
changes to secrets can be reviewed before they are merged
- this leads to less fuck-ups on deployments
“everything” is in the repository, which brings a lot of familiar benefits like
- version control
- a single git pull is the only thing you need to get everything (=> good dev experience)

Cons

some overhead during onboarding and offboarding
the secret key must be put in the root of the repository at ./secret.gpg
no fine grained permissions for different secrets, e.g. the mysql password on production and
staging can not be treated differently
- if somebody can decrypt secrets, ALL of them are exposed
if the a secret key ever gets leaked, all secrets are compromised
- => can be mitigated (to a degree) by using a passphrase on the secret key
- => this is kinda true for any other system that stores secrets as well BUT third parties
  could probably implement additional measures like multi factor authentication
secrets are versioned alongside the users that have access, i.e. even if a user is removed at
some point, he can still decrypt a previous version of the encrypted secrets

Wrapping up

Congratulations, you made it! If some things are not completely clear by now, don’t hesitate to
leave a comment. You are now able to encrypt and decrypt secret files so that they can be stored
directly in the git repository.

In the next part of this tutorial, we will
set up a CI pipeline for dockerized PHP Apps on Github and Gitlab
that decrypts all necessary secrets and then runs our tests and qa tools.

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notifications when this next part comes out 🙂

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Published parts of the Docker PHP Tutorial

Table of contents

Introduction

Tooling

gpg

gpg installation

gpg usage

Create GPG key pair

Export, list and import private GPG keys

Export, list and import public GPG keys

git-secret

git-secret installation

git-secret usage

Initialize git-secret

The git-secret directory and the gpg-agent socket

Adding, listing and removing users

Reminder: Rotate the encrypted secrets

Adding, listing and removing files for encryption

Encrypt files

Decrypting files

Show changes between encrypted and decrypted files

Makefile adjustments

Workflow

Process challenges

Updating secrets

Code reviews and merge conflicts

Local git-secret and gpg setup

Scenarios

Initial setup of gpg keys

Initial setup of git-secret

Initialize gpg after container startup

Adding (new) team members

Adding and encrypting files

Decrypt files

Removing files

Removing team members

Pros and cons

Pro

Cons

Wrapping up

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Comments

The `git-secret` directory and the `gpg-agent` socket

Local `git-secret` and `gpg` setup

Initial setup of `gpg` keys

Initial setup of `git-secret`

Initialize `gpg` after container startup