Safely store secrets in Git/Mercurial/Subversion
Shell Makefile
Latest commit bd0fcd1 Jan 20, 2017 @tolbrino tolbrino committed with tlimoncelli [FreeBSD] Fix use of chmod (#180)
LGTM

Thanks for the fix!

README.md

BlackBox

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.

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 is easy. Just cd into a Git, Mercurial, Subversion or Perforce 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 theblackbox_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 practitioniers need to do.

Installation Instructions:

  • 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.
  • The Debian/Ubuntu way: Check out the repo and install fpm. Now you can make a DEB make packages-deb that can be distributed via local methods.
  • The hard way: Copy all the files in "bin" to your "bin".
  • The manual way: make manual-install to install. make manual-uninstall to uninstall.
  • 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_edit <file> Decrypt, run $EDITOR, re-encrypt a file
blackbox_edit_start <file> Decrypt a file so it can be updated
blackbox_edit_end <file> Encrypt a file after blackbox_edit_start was used
blackbox_cat <file> Decrypt and view the contents of a file
blackbox_diff Diff decrypted files against their original crypted version
blackbox_initialize Enable blackbox for a GIT or HG repo
blackbox_register_new_file <file> Encrypt a file for the first time
blackbox_deregister_file <file> Remove a file from blackbox
blackbox_list_files List the files maintained by blackbox
blackbox_list_admins List admins currently authorized for blackbox
blackbox_decrypt_all_files Decrypt all managed files (INTERACTIVE)
blackbox_postdeploy Decrypt all managed files (batch)
blackbox_addadmin <gpg-key> Add someone to the list of people that can encrypt/decrypt secrets
blackbox_removeadmin <gpg-key> 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
blackbox_whatsnew <file> 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 keyrings directory is intact
  • Operating system
    • CentOS / RedHat
    • MacOS X
    • Cygwin (Thanks, Ben Drasin!)
    • MinGW (git bash on windows) See Note Below

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 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)

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

  • 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

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 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 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?

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.

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

gpg --gen-key

Pick defaults for encryption settings, 0 expiration. Pick a VERY GOOD passphrase. Store the private key securely. Tip: Store it on a secure machine, or one with little or no internet access, with full-disk-encryption, etc. Your employer problably has rules about how to store such things.

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 tal@example.com

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: tal@example.com' keyrings/live/pubring.gpg keyrings/live/trustdb.gpg keyrings/live/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 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.

Pre-check: Verify the new keys look good.

$ gpg --homedir=keyrings/live --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 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.

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*

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.

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.

Replace expired keys:

If any one admin's key expires, you can no longer encrypt files. You will need to replace the key and re-encrypt.

  • Step 0: You see this error:
$ blackbox_edit_end modified_file.txt
--> Error: can't re-encrypt because a key has expired.
  • Step 1. Administrator removes expired user:

Warning: This process will erase any unencrypted files that you were in the process of editing. Copy them elsewhere and restore the changes when done.

blackbox_removeadmin expired_user@example.com
# This next command overwrites any changed unencrypted files. See warning above.
blackbox_update_all_files
git commit -m "Re-encrypt all files"
gpg --homedir=keyrings/live --delete-key expired_user@example.com
git commit -m 'Cleaned expired_user@example.com from keyring'  keyrings/live/*
git push
  • Step 2. Expired user adds an updated key:
git pull
blackbox_addadmin updated_user@example.com
git commit -m'NEW ADMIN: updated_user@example.com keyrings/live/pubring.gpg keyrings/live/trustdb.gpg keyrings/live/blackbox-admins.txt
git push
  • Step 3. Administrator re-encrypts all files with the updated key of the expired user:
git pull
gpg --import keyrings/live/pubring.gpg 
blackbox_update_all_files 
git commit -m "Re-encrypt all files"
git push
  • Step 4: Clean up:

Any files that were temporarily copied in the first step so as to not be overwritten can now be copied back and re-encrypted with the blackbox_edit_end command.

(Thanks to @chishaku for finding a solution to this problem!)

Configure git to show diffs in encrypted files

It's possible to tell Git to decrypt versions of the file before running them through git diff or git log. To achieve this do:

  • Add the following to .gitattributes at the top of the git repository:
*.gpg diff=blackbox
  • Add the following to .git/config:
[diff "blackbox"]
    textconv = gpg --use-agent -q --batch --decrypt

And now commands like git log -p file.gpg will show a nice log of the changes in the encrypted file.

Some common errors:

gpg: filename: skipped: No public key -- Usually this means there is an item in keyrings/live/blackbox-admins.txt that is not the name of the key. Either something invalid was inserted (like a filename instead of a username) or a user has left the organization and their key was removed from the keychain, but their name wasn't removed from the blackbox-admins.txt file.

gpg: decryption failed: No secret key -- Usually means you forgot to re-encrypt the file with the new key.

Error: can't re-encrypt because a key has expired. -- A user's key has expired and can't be used to encrypt any more. Follow theReplace expired keys tip.

Using Blackbox without a repo

If the files are copied out of a repo they can still be decrypted and edited. Obviously edits, changes to keys, and such will be lost if they are made outside the repo. Also note that commands are most likely to only work if run from the base directory (i.e. the parent to the keyrings directory).

The following commands have been tested outside a repo:

  • blackbox_postdeploy
  • blackbox_edit_start
  • blackbox_edit_end

Some Subversion gotchas:

The current implementation will store the blackbox in /keyrings at the root of the entire repo. this will create an issue between environments that have different roots (ie, checking out / on development vs /releases/foo in production). To get around this, you can export BLACKBOX_REPOBASE=/path/to/repo and set a specific base for your repo.

This was originally written for git and supports a two-phase commit, in which commit is a local commit and "push" sends the change upstream to the version control server when something is registered or deregistered with the system. The current implementation will immediately commit a file (to the upstream subversion server) when you execute a blackbox_* command.

How to submit bugs or ask questions?

We welcome questions, bug reports and feedback!

Developer Info

Code submissions are gladly welcomed! The code is fairly easy to read.

Get the code:

git clone git@github.com:StackExchange/blackbox.git

Test your changes:

make confidence

This runs through a number of system tests. It creates a repo, encrypts files, decrypts files, and so on. You can run these tests to verify that the changes you made didn't break anything. You can also use these tests to verify that the system works with a new operating system.

Please submit tests with code changes:

The best way to change Blackbox is via Test Driven Development. First add a test to tools/confidence.sh. This test should fail, and demonstrate the need for the change you are about to make. Then fix the bug or add the feature you want. When you are done, make confidence should pass all tests. The PR you submit should include your code as well as the new test. This way the confidence tests accumulate as the system grows as we know future changes don't break old features.

Note: The tests currently assume "git" and have been tested only on CentOS, Mac OS X, and Cygwin. Patches welcome!

Alternatives

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

git-crypt has the best git integration. Once set up it is nearly transparent to the users. However it only works with git.

License

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