Encrypted Configuration on Rails 5.2

Credentials is a new feature on Rails 5.2 which replaces secrets and encrypted secrets. Under the hood Credentials use EncryptedConfiguration which you can reuse if you need to use encryption on other parts of your application.

If you only want to use the credentials on config/credentials.yml.enc, Rails has special methods for that like Rails.application.credentials. 

This blog post is for using EncryptedConfiguration with other files.

EncryptedConfiguration

You can use EncryptedConfiguration through Rails.application.encrypted. Let’s say you want to encrypt some data and save the encrypted file on top_secret.txt.enc.

encrypted = Rails.application.encrypted('top_secret.txt.enc')

This will create a new EncryptedConfiguration object which you can use to encrypt and decrypt text.

encrypted.write('This is a top secret message.')

If you check the file top_secret.txt.enc, you will see

EprXfkUXq/rlKQUTPg52OMoSUWfYnPHCiYqxd9y/URvVebmmuhap--QFtMHoVUYleOY8qC--xadtJ2aVQJ2y0IDljt9yAg==

You won’t be able to decrypt this without the key. Notice that we didn’t specify any key when we called Rails.application.encrypted. If you didn’t specify any key, the default master key on config/master.key will be used. This key was created when you created your new Rails 5.2 app. If it doesn’t exist, a key will be created when you run bin/rails credentials:edit.

If you want to use a different key aside from config/master.key, create one by running

ActiveSupport::EncryptedConfiguration.generate_key

You can run this on rails console or from the command line you can run

bundle exec rails runner 'puts ActiveSupport::EncryptedConfiguration.generate_key'

0dbcb53a3e52e6b983bd75d932dca52c

The output is a string with a length of 32. It’s actually a hex as SecureRandom.hex is used.

Save the key to a file. If you use config/top_secret.key as the file name, you can get the EncryptedConfiguration object with

encrypted = Rails.application.encrypted('top_secret.txt.enc', key_path: 'config/top_secret.key')

Then you can write your encrypted text like before.

encrypted.write('This is a top secret message.')

To decrypt the text, run

encrypted.read
=> 'This is a top secret message.' 

Currently, there’s no way to open an editor with the decrypted text when using a custom filename. With credentials, you can run bin/rails credentials:edit to open a decrypted version of your credentials from config/credentials.yml.enc.

Conclusion

EncyptedConfiguration is the underlying code that makes credentials work. You don’t need to use it directly but if you have custom needs, give it a try. Rails encourages using it instead of rolling out your own encryption code.