BlackBox

Safely store secrets in a VCS repo (i.e. Git, Mercurial, or Subversion). 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.

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 is easy. Just cd into a Git, Mercurial or Subversion repository and run blackbox_initialize. After that, if a file is to be encrypted, run blackbox_register_new_file and you are done. Add and remove keys with blackbox_addadmin and blackbox_removeadmin. 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. Communciation 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 practitioniers need to do.

Installation Instructions:

• The MacPorts Way: sudo port install vcs_blackbox
• The RPM way: make packages-rpm and now you have an RPM you can install.
• The Debian/Ubuntu way: make packages-deb and now you have a DEB you can install.
• The hard way: Copy all the files in "bin" to your "bin".
• 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.

Commands:

Name:	Description:
blackbox_addadmin	Add someone to the list of people that can encrypt/decrypt secrets
blackbox_cat	Decrypt and view the contents of a file
blackbox_diff	Diff decrypted files against their original crypted version
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 blackbox_edit_start was used
blackbox_initialize	Enable blackbox for a GIT or HG repo
blackbox_postdeploy	Decrypt all managed files
blackbox_register_new_file	Encrypt a file for the first time
blackbox_removeadmin	Remove someone from the list of people that can encrypt/decrypt secrets
blackbox_shred_all_files	Safely delete any decrypted files
blackbox_update_all_files	Decrypt then re-encrypt all files. Useful after keys are changed

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!)
• Operating system
  • CentOS / RedHat
  • MacOS X
  • Cygwin (Thanks, Ben Drasin!)

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

Note: Cywin support requires the following packages:

• Normal operation:
  • gnupg
  • git or mercurial or subversion (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)

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 messsage.

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 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 than! 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 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

How to remove a file from the system?

This is a manual process. It happens quite rarely.

1. Remove the file keyrings/live/blackbox-files.txt
2. Remove references from .gitignore or .hgignore
3. Use git rm or hg rm as expected.

How to indoctrinate a new user into the system?

keyrings/live/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.

gpg --gen-key

Pick defaults for encryption settings, 0 expiration. Pick a VERY GOOD passphrase.

blackbox_addadmin KEYNAME

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

blackbox_addadmin tal@example.com

When the command completes successfully, instructions on how to commit these changes will be output. Run the command as give.

NEXT STEP: Check these into the repo.  Probably with a command like...
git commit -m'NEW ADMIN: tal@example.com' keyrings/live/pubring.gpg keyrings/live/trustdb.gpg keyrings/live/blackbox-admins.txt

Role accounts: 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 puppetmaster@puppet-master-1.example.com /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:

gpg --import keyrings/live/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 olduser@example.com
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.

gpg --homedir=keyrings/live --list-keys
gpg --homedir=keyrings/live --delete-key olduser@example.com
git commit -m'Cleaned olduser@example.com from keyring'  keyrings/live/*

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.

First Time Setup (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 "keyrings".
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.

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*

Push these changes to the repo. Make sure another user can check out and change the contents of the file.

Set up automated users or "role accounts"

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

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: svc_deployacct@hostname.domain.name

NOTE: Rather than a real email address, use the username@FQDN 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 username@FQDN 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

Back on SECUREHOST, add the new email address to keyrings/live/blackbox-admins.txt:

cd /path/to/the/repo
blackbox_addadmin $KEYNAME /tmp/NEWMASTER

Verify that secring.gpg is a zero-length file. If it isn't, you have somehow added a private key to the keyring. Start over.

$ cd keyrings/live
$ ls -l secring.gpg

Commit the recent changes:

$ cd keyrings/live
git commit -m"Adding key for KEYNAME" pubring.gpg trustdb.gpg blackbox-admins.txt

Regenerate all encrypted files with the new key:

blackbox_update_all_files
git status
git commit -m"updated encryption" -a
git push

On NEWMASTER, import the keys and decrypt the files:

sudo -u svc_sadeploy bash   # Become the role account.
gpg --import /etc/puppet/keyrings/live/pubring.gpg
export PATH=$PATH:/path/to/blackbox/bin
blackbox_postdeploy
sudo -u puppet cat /etc/puppet/hieradata/blackbox.yaml # or any encrypted file.

ProTip: If you get "gpg: decryption failed: No secret key" then you forgot to re-encrypt blackbox.yaml with the new key.

On SECUREHOST, securerly delete your files:

cd /tmp/NEWMASTER
# On machines with the "shred" command:
shred -u /tmp/keys.tar
find . -type f -print0 | xargs -0 shred -u
# All else:
rm -rf /tmp/NEWMASTER

Also shred any other temporary files you may have made.

Help out: Submit bugs, pull requests and ideas:

I welcome code changes, questions, bug reports and feedback!

• Submit code: https://github.com/StackExchange/blackbox
• Report bugs/questions: https://github.com/StackExchange/blackbox/issues

Tip for submitting code:

After you make a change, please re-run the confidence tests. This runs through various procedures and checks the results.

To run the tests:

make confidence

Note: The tests currently assume "git" and have been tested on CentOS and Cygwin.

Alternatives

Here are other open source packages that do something similar to Blackbox. If you like them better than Blackbox, please use them.

• Pass: http://www.zx2c4.com/projects/password-store/
• Transcrypt: https://github.com/elasticdog/transcrypt
• git-crypt: https://www.agwa.name/projects/git-crypt/

License

This content is released under the MIT License. See the LICENSE.txt file.