blackbox

by StackExchange

StackExchange / blackbox

Safely store secrets in Git/Mercurial/Subversion

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BlackBox CircleCI

Safely store secrets in a VCS repo (i.e. Git, Mercurial, Subversion or Perforce). These commands make it easy for you to Gnu Privacy Guard (GPG) encrypt specific files in a repo so they are "encrypted at rest" in your repository. However, the scripts make it easy to decrypt them when you need to view or edit them, and decrypt them for use in production. Originally written for Puppet, BlackBox now works with any Git or Mercurial repository.

A slide presentation about an older release is on SlideShare.

Join our mailing list: https://groups.google.com/d/forum/blackbox-project

Table of Contents

Overview

Suppose you have a VCS repository (i.e. a Git or Mercurial repo) and certain files contain secrets such as passwords or SSL private keys. Often people just store such files "and hope that nobody finds them in the repo". That's not safe.

With BlackBox, those files are stored encrypted using GPG. Access to the VCS repo without also having the right GPG keys makes it worthless to have the files. As long as you keep your GPG keys safe, you don't have to worry about storing your VCS repo on an untrusted server. Heck, even if you trust your server, now you don't have to trust the people that do backups of that server, or the people that handle the backup tapes!

Rather than one GPG passphrase for all the files, each person with access has their own GPG keys in the system. Any file can be decrypted by anyone with their GPG key. This way, if one person leaves the company, you don't have to communicate a new password to everyone with access. Simply disable the one key that should no longer have access. The process for doing this is as easy as running 2 commands (1 to disable their key, 1 to re-encrypt all files.)

Automated processes often need access to all the decrypted files. This is easy too. For example, suppose Git is being used for Puppet files. The master needs access to the decrypted version of all the files. Simply set up a GPG key for the Puppet master (or the role account that pushes new files to the Puppet master) and have that user run

blackbox_postdeploy
after any files are updated.

Getting started

  1. If you don't have a GPG key, set it up using instructions such as: Set up GPG key. \ Now you are ready to go.

  2. cd
    into a Git, Mercurial, Subversion or Perforce repository and run
    blackbox_initialize
    .
  3. If a file is to be encrypted, run

    blackbox_register_new_file
    and you are done.
  4. Add and remove keys with

    blackbox_addadmin
    and
    blackbox_removeadmin
    .
  5. To view and/or edit a file, run

    blackbox_edit
    ; this will decrypt the file and open with whatever is specified by your $EDITOR environment variable. \ When you close the editor the file will automatically be encrypted again and the temporary plaintext file will be shredded. \ If you need to leave the file decrypted while you update you can use the
    blackbox_edit_start
    to decrypt the file and
    blackbox_edit_end
    when you want to "put it back in the box."

Why is this important?

OBVIOUSLY we don't want secret things like SSL private keys and passwords to be leaked.

NOT SO OBVIOUSLY when we store "secrets" in a VCS repo like Git or Mercurial, suddenly we are less able to share our code with other people. Communication between subteams of an organization is hurt. You can't collaborate as well. Either you find yourself emailing individual files around (yuck!), making a special repo with just the files needed by your collaborators (yuck!!), or just deciding that collaboration isn't worth all that effort (yuck!!!).

The ability to be open and transparent about our code, with the exception of a few specific files, is key to the kind of collaboration that DevOps and modern IT practitioners need to do.

Installation Instructions

  • The hard way (manual): Copy all the files in "bin" to your "bin".
  • The hard way (automatic):
    make copy-install
    will copy the bin files into $PREFIX/bin, default is /usr/local (uninstall with
    make copy-uninstall
    ).
  • The symlinks way:
    make symlinks-install
    will make symlinks of the bin files into $PREFIX/bin, default is /usr/local (uninstall with
    make copy-uninstall
    ) (useful when doing development)
  • The MacPorts Way:
    sudo port install vcs_blackbox
  • The Homebrew Way:
    brew install blackbox
  • The RPM way: Check out the repo and make an RPM via
    make packages-rpm
    ; now you can distribute the RPM via local methods. (Requires fpm.)
  • The Debian/Ubuntu way: Check out the repo and make a DEB via
    make packages-deb
    ; now you can distribute the DEB via local methods. (Requires fpm.)
  • The Antigen Way: Add
    antigen bundle StackExchange/blackbox
    to your .zshrc
  • The Zgen Way: Add
    zgen load StackExchange/blackbox
    to your .zshrc where you're loading your other plugins.
  • The Nix Way:
    nix-env -i blackbox
  • The Pkgsrc Way:
    pkgin in scm-blackbox

Commands

| Name: | Description: | |-------------------------------------|-------------------------------------------------------------------------| |

blackbox_edit 
| Decrypt, run $EDITOR, re-encrypt a file | |
blackbox_edit_start 
| Decrypt a file so it can be updated | |
blackbox_edit_end 
| Encrypt a file after blackboxeditstart was used | |
blackbox_cat 
| Decrypt and view the contents of a file | |
blackbox_view 
| Like blackboxcat but pipes to
less
or $PAGER | | `blackbox
diff
| Diff decrypted files against their original crypted version             |
|
blackboxinitialize
| Enable blackbox for a GIT or HG repo                                    |
|
blackbox
registernewfile
| Encrypt a file for the first time                                       |
|
blackboxderegisterfile
| Remove a file from blackbox                                             |
|
blackboxlistfiles
| List the files maintained by blackbox                                   |
|
blackboxlistadmins
| List admins currently authorized for blackbox                           |
|
blackboxdecryptfile
| Decrypt a file                                                          |
|
blackboxdecryptallfiles
| Decrypt all managed files (INTERACTIVE)                                 |
|
blackbox
postdeploy
| Decrypt all managed files (batch)                                       |
|
blackboxaddadmin
| Add someone to the list of people that can encrypt/decrypt secrets      |
|
blackbox
removeadmin
| Remove someone from the list of people that can encrypt/decrypt secrets |
|
blackboxshredallfiles
| Safely delete any decrypted files                                       |
|
blackbox
updateallfiles
| Decrypt then re-encrypt all files. Useful after keys are changed        |
|
blackbox_whatsnew ` | show what has changed in the last commit for a given file |

Compatibility

BlackBox automatically determines which VCS you are using and does the right thing. It has a plug-in architecture to make it easy to extend to work with other systems. It has been tested to work with many operating systems.

  • Version Control systems
    • git
      -- The Git
    • hg
      -- Mercurial
    • svn
      -- SubVersion (Thanks, Ben Drasin!)
    • p4
      -- Perforce
    • none -- The files can be decrypted outside of a repo if the
      .blackbox
      directory is intact
  • Operating system
    • CentOS / RedHat
    • MacOS X
    • Cygwin (Thanks, Ben Drasin!) See Note Below
    • MinGW (git bash on windows) See Note Below
    • NetBSD
    • SmartOS

To add or fix support for a VCS system, look for code at the end of

bin/_blackbox_common.sh

To add or fix support for a new operating system, look for the case statements in

bin/_blackbox_common.sh
and
bin/_stack_lib.sh
and maybe
tools/confidence_test.sh

Using BlackBox on Windows

BlackBox can be used with Cygwin or MinGW.

Protect the line endings

BlackBox assumes that

blackbox-admins.txt
and
blackbox-files.txt
will have LF line endings. Windows users should be careful to configure Git or other systems to not convert or "fix" those files.

If you use Git, add the following lines to your

.gitattributes
file:
**/blackbox-admins.txt text eol=lf
**/blackbox-files.txt text eol=lf

The latest version of

blackbox_initialize
will create a
.gitattributes
file in the
$BLACKBOXDATA
directory (usually
.blackbox
) for you.

Cygwin

Cygwin support requires the following packages:

Normal operation:

  • gnupg
  • git or mercurial or subversion or perforce (as appropriate)

Development (if you will be adding code and want to run the confidence test)

  • procps
  • make
  • git (the confidence test currently only tests git)

MinGW

MinGW (comes with Git for Windows) support requires the following:

Normal operation:

  • Git for Windows (not tested with Mercurial)
    • Git Bash MINTTY returns a MinGW console. So when you install make sure you pick
      MINTTY
      instead of windows console. You'll be executing blackbox from the Git Bash prompt.
    • You need at least version 2.8.1 of Git for Windows.
  • GnuWin32 - needed for various tools not least of which is mktemp which is used by blackbox
    • after downloading the install just provides you with some batch files. Because of prior issues at sourceforge and to make sure you get the latest version of each package the batch files handle the brunt of the work of getting the correct packages and installing them for you.
    • from a windows command prompt run
      download.bat
      once it has completed run
      install.bat
      then add the path for those tools to your PATH (ex:
      PATH=%PATH%;c:\GnuWin32\bin
      )

Development:

  • unknown (if you develop Blackbox under MinGW, please let us know if any additional packages are required to run
    make test
    )

How is the encryption done?

GPG has many different ways to encrypt a file. BlackBox uses the mode that lets you specify a list of keys that can decrypt the message.

If you have 5 people ("admins") that should be able to access the secrets, each creates a GPG key and adds their public key to the keychain. The GPG command used to encrypt the file lists all 5 key names, and therefore any 1 key can decrypt the file.

To remove someone's access, remove that admin's key name (i.e. email address) from the list of admins and re-encrypt all the files. They can still read the .gpg file (assuming they have access to the repository) but they can't decrypt it any more.

What if they kept a copy of the old repo before you removed access? Yes, they can decrypt old versions of the file. This is why when an admin leaves the team, you should change all your passwords, SSL certs, and so on. You should have been doing that before BlackBox, right?

Why don't you use symmetric keys? In other words, why mess with all this GPG key stuff and instead why don't we just encrypt all the files with a single passphrase. Yes, GPG supports that, but then we are managing a shared password, which is fraught with problems. If someone "leaves the team" we would have to communicate to everyone a new password. Now we just have to remove their key. This scales better.

How do automated processes decrypt without asking for a password? GPG requires a passphrase on a private key. However, it permits the creation of subkeys that have no passphrase. For automated processes, create a subkey that is only stored on the machine that needs to decrypt the files. For example, at Stack Exchange, when our Continuous Integration (CI) system pushes a code change to our Puppet masters, they run

blackbox_postdeploy
to decrypt all the files. The user that runs this code has a subkey that doesn't require a passphrase. Since we have many masters, each has its own key. And, yes, this means our Puppet Masters have to be very secure. However, they were already secure because, like, dude... if you can break into someone's puppet master you own their network.

If you use Puppet, why didn't you just use hiera-eyaml? There are 4 reasons:

  1. This works with any Git or Mercurial repo, even if you aren't using Puppet.
  2. hiera-eyaml decrypts "on demand" which means your Puppet Master now uses a lot of CPU to decrypt keys every time it is contacted. It slows down your master, which, in my case, is already slow enough.
  3. This works with binary files, without having to ASCIIify them and paste them into a YAML file. Have you tried to do this with a cert that is 10K long and changes every few weeks? Ick.
  4. hiera-eyaml didn't exist when I wrote this.

What does this look like to the typical user?

  • If you need to, start the GPG Agent:
    eval $(gpg-agent --daemon)
  • Decrypt the file so it is editable:
    blackbox_edit_start FILENAME
  • (You will need to enter your GPG passphrase.)
  • Edit FILENAME as you desire:
    vim FILENAME
  • Re-encrypt the file:
    blackbox_edit_end FILENAME
  • Commit the changes.
    git commit -a
    or
    hg commit

Wait... it can be even easier than that! Run

blackbox_edit FILENAME
, and it'll decrypt the file in a temp file and call
$EDITOR
on it, re-encrypting again after the editor is closed.

How to use the secrets with Ansible?

Ansible Vault provides functionality for encrypting both entire files and strings stored within files; however, keeping track of the password(s) required for decryption is not handled by this module.

Instead one must specify a password file when running the playbook.

Ansible example for password file:

my_secret_password.txt.gpg
ansible-playbook --vault-password-file my_secret_password.txt site.yml

Alternatively, one can specify this in the

ANSIBLE_VAULT_PASSWORD_FILE
environment variable.

How to use the secrets with Puppet?

Entire files:

Entire files, such as SSL certs and private keys, are treated just like regular files. You decrypt them any time you push a new release to the puppet master.

Puppet example for an encrypted file:

secret_file.key.gpg
file { '/etc/my_little_secret.key':
    ensure  => 'file',
    owner   => 'root',
    group   => 'puppet',
    mode    => '0760',
    source  => "puppet:///modules/${module_name}/secret_file.key",
}

Small strings:

Small strings, such as passwords and API keys, are stored in a hiera yaml file, which you encrypt with

blackbox_register_new_file
. For example, we use a file called
blackbox.yaml
. You can access them using the hiera() function.

Setup: Configure

hiera.yaml
by adding "blackbox" to the search hierarchy:
:hierarchy:
  - ...
  - blackbox
  - ...

In blackbox.yaml specify:

---
module::test_password: "my secret password"

In your Puppet Code, access the password as you would any hiera data:

$the_password = hiera('module::test_password', 'fail')

file {'/tmp/debug-blackbox.txt': content => $the_password, owner => 'root', group => 'root', mode => '0600', }

The variable

$the_password
will contain "my secret password" and can be used anywhere strings are used.

How to enroll a new file into the system?

  • If you need to, start the GPG Agent:
    eval $(gpg-agent --daemon)
  • Add the file to the system:
blackbox_register_new_file path/to/file.name.key

Multiple file names can be specified on the command line:

Example 1: Register 2 files:

blackbox_register_new_file file1.txt file2.txt

Example 2: Register all the files in

$DIR
:
find $DIR -type f -not -name '*.gpg' -print0 | xargs -0 blackbox_register_new_file

How to remove a file from the system?

This happens quite rarely, but we've got it covered:

blackbox_deregister_file path/to/file.name.key

How to indoctrinate a new user into the system?

FYI: Your repo may use

keyrings/live
instead of
.blackbox
. See "Where is the configuration stored?"

.blackbox/blackbox-admins.txt
is a file that lists which users are able to decrypt files. (More pedantically, it is a list of the GnuPG key names that the file is encrypted for.)

To join the list of people that can edit the file requires three steps; You create a GPG key and add it to the key ring. Then, someone that already has access adds you to the system. Lastly, you should test your access.

Step 1: YOU create a GPG key pair on a secure machine and add to public keychain.

If you don't already have a GPG key, here's how to generate one:

gpg --gen-key

WARNING: New versions of GPG generate keys which are not understood by old versions of GPG. If you generate a key with a new version of GPG, this will cause problems for users of older versions of GPG. Therefore it is recommended that you either assure that everyone using Blackbox have the exact same version of GPG, or generate GPG keys using a version of GPG as old as the oldest version of GPG used by everyone using Blackbox.

Pick defaults for encryption settings, 0 expiration. Pick a VERY GOOD passphrase. Store a backup of the private key someplace secure. For example, keep the backup copy on a USB drive that is locked in safe. Or, at least put it on a secure machine with little or no internet access, full-disk-encryption, etc. Your employer probably has rules about how to store such things.

FYI: If generating the key is slow, this is usually because the system isn't generating enough entropy. Tip: Open another window on that machine and run this command:

ls -R /

Now that you have a GPG key, add yourself as an admin:

blackbox_addadmin KEYNAME

...where "KEYNAME" is the email address listed in the gpg key you created previously. For example:

blackbox_addadmin [email protected]

When the command completes successfully, instructions on how to commit these changes will be output. Run the command as given to commit the changes. It will look like this:

git commit -m'NEW ADMIN: [email protected]' .blackbox/pubring.gpg .blackbox/trustdb.gpg .blackbox/blackbox-admins.txt

Then push it to the repo:

git push

or

ht push

(or whatever is appropriate)

NOTE: Creating a Role Account? If you are adding the pubring.gpg of a role account, you can specify the directory where the pubring.gpg file can be found as a 2nd parameter:

blackbox_addadmin [email protected] /path/to/the/dir

Step 2: SOMEONE ELSE adds you to the system.

Ask someone that already has access to re-encrypt the data files. This gives you access. They simply decrypt and re-encrypt the data without making any changes.

Pre-check: Verify the new keys look good.

git pull    # Or whatever is required for your system
gpg --homedir=.blackbox --list-keys

For example, examine the key name (email address) to make sure it conforms to corporate standards.

Import the keychain into your personal keychain and reencrypt:

gpg --import .blackbox/pubring.gpg
blackbox_update_all_files

Push the re-encrypted files:

git commit -a
git push

or

hg commit hg push

Step 3: YOU test.

Make sure you can decrypt a file. (Suggestion: Keep a dummy file in VCS just for new people to practice on.)

How to remove a user from the system?

Simply run

blackbox_removeadmin
with their keyname then re-encrypt:

Example:

blackbox_removeadmin [email protected]
blackbox_update_all_files

When the command completes, you will be given a reminder to check in the change and push it.

Note that their keys will still be in the key ring, but they will go unused. If you'd like to clean up the keyring, use the normal GPG commands and check in the file.

FYI: Your repo may use

keyrings/live
instead of
.blackbox
. See "Where is the configuration stored?"
gpg --homedir=.blackbox --list-keys
gpg --homedir=.blackbox --delete-key [email protected]
git commit -m'Cleaned [email protected] from keyring'  .blackbox/*

FYI: Your repo may use

keyrings/live
instead of
.blackbox
. See "Where is the configuration stored?"

The key ring only has public keys. There are no secret keys to delete.

Remember that this person did have access to all the secrets at one time. They could have made a copy. Therefore, to be completely secure, you should change all passwords, generate new SSL keys, and so on just like when anyone that had privileged access leaves an organization.

Where is the configuration stored? .blackbox vs. keyrings/live

Blackbox stores its configuration data in the

.blackbox
subdirectory. Older repos use
keyrings/live
. For backwards compatibility either will work.

All documentation refers to

.blackbox
.

You can convert an old repo by simply renaming the directory:

mv keyrings/live .blackbox
rmdir keyrings

There is no technical reason to convert old repos except that it is less confusing to users.

This change was made in commit 60e782a0, release v1.20180615.

The details:

  • First Blackbox checks
    $BLACKBOXDATA
    . If this environment variable is set, this is the directory that will be used. If it lists a directory that does not exist, Blackbox will print an error and exit.
  • If
    $BLACKBOXDATA
    is not set: (which is the typical use case)
    • Blackbox will first try
      keyrings/live
      and use it if it exists.
    • Otherwise the default
      .blackbox
      will be used. If
      .blackbox
      does not exist, Blackbox will print an error and exit.

Enabling BlackBox For a Repo

Overview:

To add "blackbox" to a git or mercurial repo, you'll need to do the following:

  1. Run the initialize script. This adds a few files to your repo in a directory called ".blackbox".
  2. For the first user, create a GPG key and add it to the key ring.
  3. Encrypt the files you want to be "secret".
  4. For any automated user (one that must be able to decrypt without a passphrase), create a GPG key and create a subkey with an empty passphrase.

FYI: Your repo may use

keyrings/live
instead of
.blackbox
. See "Where is the configuration stored?"

Run the initialize script.

You'll want to include blackbox's "bin" directory in your PATH:

export PATH=$PATH:/the/path/to/blackbox/bin
blackbox_initialize

If you're using antigen, adding

antigen bundle StackExchange/blackbox
to your .zshrc will download this repository and add it to your $PATH.

For the first user, create a GPG key and add it to the key ring.

Follow the instructions for "How to indoctrinate a new user into the system?". Only do Step 1.

Once that is done, is a good idea to test the system by making sure a file can be added to the system (see "How to enroll a new file into the system?"), and a different user can decrypt the file.

Make a new file and register it:

rm -f foo.txt.gpg foo.txt
echo This is a test. >foo.txt
blackbox_register_new_file foo.txt

Decrypt it:

blackbox_edit_start foo.txt.gpg
cat foo.txt
echo This is the new file contents. >foo.txt

Re-encrypt it:

blackbox_edit_end foo.txt.gpg
ls -l foo.txt*

You should only see

foo.txt.gpg
as
foo.txt
should be gone.

The next step is to commit

foo.txt.gpg
and make sure another user can check out, view, and change the contents of the file. That is left as an exercise for the reader. If you are feel like taking a risk, don't commit
foo.txt.gpg
and delete it instead.

Set up automated users or "role accounts"

i.e. This is how a Puppet Master can have access to the unencrypted data.

FYI: Your repo may use

keyrings/live
instead of
.blackbox
. See "Where is the configuration stored?"

An automated user (a "role account") is one that that must be able to decrypt without a passphrase. In general you'll want to do this for the user that pulls the files from the repo to the master. This may be automated with Jenkins CI or other CI system.

GPG keys have to have a passphrase. However, passphrases are optional on subkeys. Therefore, we will create a key with a passphrase then create a subkey without a passphrase. Since the subkey is very powerful, it should be created on a very secure machine.

There's another catch. The role account probably can't check files into Git/Mercurial. It probably only has read-only access to the repo. That's a good security policy. This means that the role account can't be used to upload the subkey public bits into the repo.

Therefore, we will create the key/subkey on a secure machine as yourself. From there we can commit the public portions into the repo. Also from this account we will export the parts that the role account needs, copy them to where the role account can access them, and import them as the role account.

ProTip: If asked to generate entropy, consider running this on the same machine in another window:

sudo dd if=/dev/sda of=/dev/null

For the rest of this doc, you'll need to make the following substitutions:

  • ROLEUSER: svc_deployacct or whatever your role account's name is.
  • NEWMASTER: the machine this role account exists on.
  • SECUREHOST: The machine you use to create the keys.

NOTE: This should be more automated/scripted. Patches welcome.

On SECUREHOST, create the puppet master's keys:

$ mkdir /tmp/NEWMASTER
$ cd /tmp/NEWMASTER
$ gpg --homedir . --gen-key
Your selection?
   (1) RSA and RSA (default)
What keysize do you want? (2048) DEFAULT
Key is valid for? (0) DEFAULT

Real name: Puppet CI Deploy Account

Email address: [email protected]

NOTE: Rather than a real email address, use the [email protected] of the host the key will be used on. If you use this role account on many machines, each should have its own key. By using the FQDN of the host, you will be able to know which key is which. In this doc, we'll refer to [email protected] as $KEYNAME

Save the passphrase somewhere safe!

Create a sub-key that has no password:

$ gpg --homedir . --edit-key svc_deployacct
gpg> addkey
(enter passphrase)
  Please select what kind of key you want:
   (3) DSA (sign only)
   (4) RSA (sign only)
   (5) Elgamal (encrypt only)
   (6) RSA (encrypt only)
Your selection? 6
What keysize do you want? (2048)
Key is valid for? (0)
Command> key 2
(the new subkey has a "*" next to it)
Command> passwd
(enter the main key's passphrase)
(enter an empty passphrase for the subkey... confirm you want to do this)
Command> save

Now securely export this directory to NEWMASTER:

gpg --homedir . --export -a svc_sadeploy >/tmp/NEWMASTER/pubkey.txt
tar cvf /tmp/keys.tar .
rsync -avP /tmp/keys.tar NEWMASTER:/tmp/.

On NEWMASTER, receive the new GnuPG config:

sudo -u svc_deployacct bash
mkdir -m 0700 -p ~/.gnupg
cd ~/.gnupg && tar xpvf /tmp/keys.tar

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