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Last updated: 29 Nov 2023

Handle encrypted hieradata

Hiera is a key-value lookup tool that we use for storing Puppet configuration data. We use Hiera eYAML GPG to encrypt sensitive Hiera data.

Hiera eYAML GPG acts as a backend to Hiera; like a plugin. It enables us to encrypt Hiera data using GPG keys. In our case, we encrypt the data using the GPG keys of all security-cleared developers on GOV.UK.

Hiera eYAML GPG only encrypts the Hiera values, rather than the whole file. It also encrypts each Hiera value individually, so you can see which ones changed in a git commit.

What Hiera data do we encrypt?

Currently, we only encrypt the data in the credentials files found in the hieradata/ directories of the alphagov/govuk-puppet and alphagov/govuk-secrets repositories. These files contain secrets such as passwords and private keys.

Why do we encrypt Hiera data?

We store secrets and sensitive data in a separate repository, govuk-secrets. This lets us open the govuk-puppet repository to all developers, while restricting access to the govuk-secrets repository to a small number of staff.

Deploying puppet copies govuk-secrets over the files in the govuk-puppet repository.

Even though we restrict who can see govuk-secrets, there are still downsides to storing secrets in plain text:

  • It’s dangerous to leave sensitive data unencrypted on disk. Even if everyone who has access to the govuk-secrets repository uses full disk encryption, secrets would be readable if a laptop is infected by malware, or if someone accidentally commits to a public repository or copies to an unencrypted disk.
  • GitHub notifications send secrets over plain text email if users comment on specific lines of a pull request that include changes to sensitive data.
  • A vulnerability in GitHub or an administrative error when setting access permissions could expose secrets.

By encrypting Hiera data using GPG, we can define who has access to these secrets (using GPG keys) and we have the extra protection of GPG encryption, which gives us time to change credentials when secrets are exposed.

There are no plans to merge the govuk-puppet and govuk-secrets repositories. Having them separate still provides extra protection against accidental exposure.

Common tasks for handling encrypted Hiera data

Hiera eYAML provides a command-line tool for viewing and editing encrypted data.

There is a Rakefile in the puppet/ directory of the govuk-secrets repository which wraps the Hiera eYAML tool and helps to ensure that sensitive data is only accessible to the intended recipients.

You must use the rake tasks to change encrypted Hiera data.

Prerequisites

  1. Pull the latest changes from the govuk-secrets repository.

  2. Run bundle to install dependencies.

Encrypting a Hiera key

  1. Where integration is the name of the environment whose credentials you wish to edit, cd into the relevant directory:

    cd puppet_aws

and run:

   bundle exec rake eyaml:edit[integration]

It will ask you for your GPG passphrase. If you get an error, please see the troubleshooting section below.

The above command will open a text editor (as determined by the $EDITOR environment variable) showing the undecrypted Hiera data in YAML format.

An unencrypted Hiera key and value looks like:

   password: 'thisisasecret'
  1. To encrypt the Hiera value, enclose it in square brackets prefixed with the string DEC::GPG and suffixed with a trailing exclamation mark (!).

The above example would look as follows:

   password: DEC::GPG[thisisasecret]!

Do not enclose it in single or double quotes as this will get interpreted as part of the secret.

Once you have finished, save the file and quit the editor. Hiera eYAML will encrypt your changes. If you get an error, please see the troubleshooting section below.

Note

When editing a Hiera key that has been encrypted before, you will notice a number in parentheses after the word GPG; for example: DEC(1)::GPG. You should not make any changes to the number, as Hiera eYAML GPG uses this to identify existing encrypted data.

  1. Check that the value is really encrypted! If you make a typo in your markup, Hiera eYAML doesn’t always treat it as an error.

    GIT_PAGER=‘less -S’ git diff

Managing access to encrypted Hiera data

The list of people that have access to encrypted Hiera data in stored in a recipient file specific to each environment (.rcp extension).

The production and integration files are stored in the govuk-secrets repo for AWS. There is no separate staging file; the production file is used for both staging and production.

Each line in a recipient file corresponds to a GPG fingerprint and usually is identified by a comment after the hash (#) symbol denoting its owner. Each GPG key (and owner of that key) listed in the recipient file is able to decrypt data belonging to the environment that the recipient file pertains to.

What to do when someone joins

  1. Ask the joiner to create a GPG key and send you the .asc file they created that contains their public key.

  2. Raise a PR to add the joiner’s public key (the .asc file) to the gpg_public_keys directory in govuk-secrets.

  3. Import the GPG key into your keychain (see “Get someone’s latest GPG key”)

  4. Get the fingerprint of the new GPG key by running gpg --fingerprint.

  5. Add the joiners’s GPG fingerprint to the recipient files AWS integration

  6. Ensure you have pass installed by running brew install pass.

  7. Recrypt the hieradata by running re-encrypt-all.sh <message> where <message> is something like “Adding new key for Jane Smith”.

  8. Commit your changes and raise a pull request for review.

  9. Take care when rebasing changes to main that have been merged since you started your PR. The encrypted hieradata files are effectively binary data that git’s text diff may not correctly merge. You will likely have to reset your recrypted versions and start again from the versions on main.

What to do when someone gets production access

Follow the steps above but add their GPG fingerprint to the production recipient files AWS production.

Note there are no staging recipient files - access to staging secrets is controlled by the production recipient files.

What to do when someone leaves

Remove leavers from all recipient files, so that they can no longer change credentials.

  1. Delete the leaver’s GPG fingerprint from each of the recipient files AWS integration and production. There are no staging recipient files since these are the same as the production recipient files.

  2. Delete their public key from the gpg_public_keys directory in govuk-secrets.

  3. Remove any other references to the user.

  4. Commit your changes and raise a pull request for review.

WARNING

Removing a GPG key from the recipient key and re-encrypting the credentials files does not mean that the leaver is no longer able to read the secrets it currently contains.

Anyone who has previously had access to a credentials file may have retained a copy of the data. They are still able to decrypt the current copy of the credentials file and have made unencrypted copies.

We must assume that, until the stored credentials are rotated and the credentials file is re-encrypted any secrets contained in the credentials file can still be read by anyone with a GPG key previously listed in the recipient list.

How to (re)generate GPG keys for an environment

If a new environment is added or the Puppet GPG key for an existing environment expires or is compromised, a new GPG key must be generated. This key allows Puppet to read encrypted Hiera data.

To ensure consistency, new GPG keys are generated using a template (example).

To generate a new key:

  1. Generate a random passphrase using a secure method (such as openssl with command openssl rand -base64 65 | tr -d '\n' | awk '{ print $0 }' to generate a 65 characters random string).

  2. Generate the GPG key pair (this assumes you are using GPG 2.x):

    1. Git clone the govuk-secret
    2. Create a new directory where the GPG key pair will be created: e.g. mkdir ~/new_hiera_gpg && cd ~/new_hiera_gpg
    3. Create the GPG key ring (pubring.kbx) based on the appropriate template (this will depend on the environment that you want to create the GPG key for) in govuk-secrets:
       gpg --homedir $PWD --verbose --batch --gen-key <path_to_selected_template>

    where <path_to_selected_template> is the file path of the template you want to use. You will be prompted for the passphrase 4. Extract the public key (pubring.gpg) of the GPG key pair by running:

       gpg --homedir $PWD --keyring ./pubring.kbx --export > ./pubring.gpg

    You should store this key in the appropriate location in govuk-secrets: e.g. for integration here and for production here 5. Extract the passphrase protected private key (secring.gpg) of the GPG key pair by running (you will have to supply the passphrase):

       gpg --homedir $PWD --keyring ./pubring.kbx --export-secret-key > ./secring.gpg

    You should store this key and other relevant GPG artefacts in the appropriate location in govuk-secrets: e.g. for integration here and for production here 6. You can obtain the fingerprint of the GPG key pair by running:

       gpg -n -q --import --import-options import-show pubring.gpg

    and noting the 41 character string in the output. 7. Send the key to the ubuntu key server by running:

       gpg --homedir $PWD --keyserver keyserver.ubuntu.com --send-key <fingerprint>

    where <fingerprint> was obtained above.

  3. Add the passphrase you used when creating the new GPG key to the Technical 2nd Line password store by running inside the pass directory of the govuk-secrets:

   PASSWORD_STORE_GPG_OPTS="--trust-model always" ./edit.sh 2ndline hiera-eyaml-gpg/<environment_passphrase_key>

where the <environment_passphrase_key> can be: production-gpg-key-passphrase or integration-gpg-key-passphrase depending on which environment you are modifying. Note that PASSWORD_STORE_GPG_OPTS is required here or otherwise GPG will refuse to encrypt the data since the new GPG key isn’t trusted by default.

If you get any error message, you should read the stored secret passphrase again to ensure that the correct value has been stored.

  1. Change the relevant files to remove the fingerprint of the old key and add the new fingerprint (as obtained above). If you changed:

    1. integration:

  2. Add and commit locally your changes to govuk-secrets. You can then use the re-encrypt-all.sh to re-encrypt all the relevant parts of govuk-secrets.

  3. Open a pull request with all the changes so far and get it approved and merged.

  4. Next, you need, as detailed in subsequent sections, to:

    1. Configure the Puppet Master in the relevant environment
    2. Upload the non-passphrase protected private GPG key to AWS parameter store

WARNING

If you’re generating a new key because the old one has been compromised, or if it has not yet expired, you should revoke the old key to prevent it being used.

Configuring the Puppet Master

The GPG key secring.gpg, stored in the govuk-secrets repository, must be installed on the Puppet Master so that encrypted Hiera data is available to Puppet:

  1. Create a new directory to do the GPG operations:
   mkdir ~/unprotected_gpg && cd ~/unprotected_gpg

  1. Copy in the new directory the private GPG key secring.gpg of the relevant environment from the directory in govuk-secrets.

  2. In the new directory, get the fingerprint of the GPG key by running:

   gpg -n -q --import --import-options import-show secring.gpg

and noting the 41 character string in the output.

  1. Import the private GPG key:
   gpg --homedir $PWD --import secring.gpg
  1. Extract the non-passphrase protected private key (secring_unprotected.gpg) by running: gpg --homedir $PWD --edit-key <finderprint> where <fingerprint> was obtained in the previous step. You will then enter the GPG prompt where you should type passwd. You will then be asked to provide the current passphrase of the private key and afterwards, you will be asked to provide a new passphrase which should be empty/nothing. You may get a prompt asking to confirm that you want to unprotect the key and you should confirm yes. You can quit the GPG prompt by typing quit

You can extract the unprotected key by exporting it:

   gpg --homedir $PWD --export-secret-key <fingerprint> > secring_unprotected.gpg

where <fingerprint> is the fingerprint obtained above.

  1. SSH to the Puppet Master (for example, puppetmaster-1.management.staging).

  2. Change to the root user (sudo su -).

  3. Go to /etc/puppet/gpg directory.

  4. Create a new folder (for example, old) and move all files currently in the gpg folder into there as a backup.

  5. Copy the following files to the Puppet Master using from your local machine:

    1. secring_unprotected.gpg as /etc/puppet/gpg/secring.gpg on puppetmaster
    2. pubring.gpg (obtained from the appropriate environment/directory in here) as /etc/puppet/gpg/pubring.gpg on puppetmaster.

  6. Make sure the new files have the correct permissions: sudo chown -R puppet:puppet /etc/puppet/gpg and sudo chmod -R 0700 /etc/puppet/gpg.

  7. Re-deploy Puppet to pick up the changes.

WARNING

Make sure not to copy the production GPG key to the integration environment.

Note

In the time between adding the new keys to the Puppet Master, deploying puppet, and it running on all machines in the relevant environment, you will see alerts in Icinga about puppet not being able to read config files. These alerts will go away as each machine runs puppet.

Uploading private GPG key to AWS parameter store

The non-passphrase protected private GPG key must be uploaded to the AWS parameter store so that if puppet is re-provisioned in AWS, the new instance of puppet will automatically get the private GPG key to decrypt the secret hiera.

This can be done by:

  1. Follow the steps in section Configuring the Puppet Master to get the non-passphrase protected private GPG key.

  2. Split the non-passphrase protected GPG key into 3 parts due to the issue that the AWS parameter store has a size limit per item. This can be done by running:

   base64 secring_unprotected.gpg > secring_unprotected.gpg.base64
   tr -d 'n' < secring_unprotected.gpg.base64 > secring_unprotected.gpg.base64.trimmed
   split -b 4096 secring_unprotected.gpg.base64.trimmed secring_unprotected_part_

You will obtained a number of files with name starting with secring_unprotected_part_.

  1. Upload the secring_unprotected_part_ parts to AWS parameter store:

    1. Login to the AWS web console of the environment to be modified
    2. Browse to the AWS Systems Manager and then to the Parameter Store ( link is usually at the bottom of the left column of the Systems Manager)
    3. There will be 3 keys with prefix: govuk_base64_gpg_ which you should update with the content of the files secring_unprotected_part_

Troubleshooting

Encryption fails when running the Rake task

If the rake task to edit the encrypted credentials fails, with errors such as:

$ bundle exec rake eyaml:edit[integration]
[gpg] !!! Warning: General exception decrypting GPG file
[hiera-eyaml-core] !!! Bad file descriptor

Check that you’re using GPG version 2 or above. Hiera eYAML GPG appears to fail when using GPG version 1 with lots of credentials.

If you see this error:

keyserver receive failed: Network is unreachable

Run this command to add standard-resolver to dirmngr.conf

echo "standard-resolver" >> ~/.gnupg/dirmngr.conf
gpgconf --kill all

If you see this error:

General error

Try pulling main again - there’s a good chance someone has made a change since you made your changes. Otherwise, check if any of the GPG keys in the recipients list have expired.

If you see this error:

[hiera-eyaml-core] !!! Bad passphrase

Check that your GPG configuration is sane. Try encrypting and decrypting some text using the gpg command:

echo 'foo' | gpg --armor --encrypt --recipient matt.bostock@digital.cabinet-office.gov.uk | gpg --decrypt

The gpg command above might give a more useful error message than the gpgme library, which Hiera eYAML GPG uses.

If you see this error:

[hiera-eyaml-core] !!! Decryption failed

Make sure that another PR re-encrypting the credentials was not merged before your one. If this is the case, the credentials will need to be re-encrypted again, making sure that your GPG key fingerprint is in the relevant recipient files.

If you see this error:

[hiera-eyaml-core] No key found on keyring for <fingerprint>

This means that you don’t have one of the recipient’s key on your keyring. You can import all public keys with the following command:

gpg --import ~/govuk/govuk-secrets/gpg_public_keys/*.asc

More information can be found in the govuk-secrets README.

Encryption fails when running the Rake task because of “Unusable public key”

You may encounter an error with the following output after trying to encrypt secrets using the Rake task:

[hiera-eyaml-core] Unusable public key

If prefixed with “There is no assurance this key belongs to the named user”, then you likely just need to run the trust script:

./pass/trust_all.sh 2ndline

Otherwise, this error may be due to an expired key or subkey.

Check keys are not expired by running the following:

cat ~/govuk/govuk-secrets/puppet_aws/gpg_recipients/production_hiera_gpg.rcp | cut -f 1 -d " " | xargs -I{} -n1 gpg --list-options show-unusable-subkeys --list-keys {}

You can check the output for any keys that may have expired, or pipe the output into grep:

| grep expired

If a key has expired, it’s possible that your local copy of the key is out of date. Follow the steps below, and if that doesn’t resolve the issue, contact the owner and ask them to extend the expiry date or renew their key, then repeat the steps below.

Get someone’s latest GPG key

Pull the latest version of the govuk-secrets repo, then import all keys again.

cd ~/govuk/govuk-secrets
git pull
gpg --import ./gpg_public_keys/*.asc

Decryption fails with “No secret key”

If you see the following error when trying to decrypt a GPG file:

[gpg] Warning: General exception decrypting GPG file
[hiera-eyaml-core] No secret key

…this suggests you don’t have permission to decrypt the file.

Make sure you’ve followed the “What to do when someone gets production access” instructions and that someone with production access has re-encrypted the secrets with your GPG key included.

Puppet fails because it can’t find a usable GPG key

When Puppet runs, you may see the following error:

Hiera eYAML GPG encryption backend is not working; check that Puppet has a valid GPG key

This error can occur for the following reasons:

  • Puppet cannot find a GPG keyring in /etc/puppet/gpg. This should only occur in development or test VMs or on the Puppet Master. Check that you have copied the GPG keys from the 2ndline pass store to /etc/puppet/gpg - see configuring the Puppet Master. Servers running puppet-agent do not require a GPG key as they rely on the Puppet Master to provide and, when necessary, decrypt Hiera data.
  • The GPG key has expired; it should be replaced with a new key - see how to (re)generate GPG keys for an environment.
  • The Hiera YAML files contain encrypted data for which the GPG keys in /etc/puppet/gpg is not listed as a recipient. Check the GPG recipient files and compare the fingerprint there to the fingerprint of the GPG keyring in /etc/puppet/gpg. You can find the fingerprint by executing the following command on the server:
  GNUPGHOME=/etc/puppet/gpg gpg --fingerprint

Puppet fails because it can’t find gpgme

You can add the $LOAD_PATH to /usr/bin/puppet as shown in this commit.

zsh: no matches found

If you encounter an error similar to

zsh: no matches found: eyaml:edit[integration]

Try either enclosing the rake command in single quotes or set the noglob option.

noglob bundle exec rake eyaml:edit[integration]

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