Sensitive data encryption in Rails
Tags: rails, lockbox, ruby, security
Published: 2020-07-29 18:40:28

---
title: Sensitive data encryption in Rails
published: true
description: migrating plaintext to ciphertext using Lockbox
tags: rails, lockbox, ruby, security
//cover_image: https://direct_url_to_image.jpg
---

Recently I received a request to encrypt some part of data that was already in my client’s app. I don’t want to share too many details, so let’s say it was few columns of an existing table that already contained some data.

So my task was to enrypt all existing records, delete non-encrypted data and save all future records as encrypted. Sounds cool!

**Lockbox**
What I needed was a simple ruby gem that would help me with all above tasks. I found [Lockbox](https://github.com/ankane/lockbox) or - the Lockbox found me! I’ve read about it some time ago in RubyWeekly newsletter. It offers migrating existing data, encrypting columns, decrypting fields on the fly if you need to display them somewhere in the views, etc.

**The Plan**
Since our app is used 24/7 we didn’t want to put it in the maintenance mode, we had to split update into few steps without causing any downtime.
I came up with this solution:
1. Add Lockbox to gemfile, add new columns to persist encrypted data, update model to migrate existing data
2. Add `ignored_columns` attribute to model (to remove columns in next step without any downtime)
3. Remove non-encrypted columns from table
4. Remove `ignored_columns` attribute

This required 4 pull requests creation, 1 task execution and zero downtime :)

**Execution**
I started by adding `gem 'lockbox', '~> 0.4.6'` to the Gemfile and generating Lockbox master key.
```ruby
Lockbox.generate_key
```
This key had to be added to all secrets (in dev, staging, production and test environments). I also created `lockbox.rb` file inside `initializers/` folder.

After that Lockbox was ready to go, so I could start work on encryption of my desired model. Let’s say that I wanted encrypt our clients’ correspondence data. Inside `Client::Address` model, I had to encrypt following fields: `street`, `city`, `postal_code`, `country`, `phone_number`

So inside `models/client/address.rb` I had to add:
```ruby
class Client::Address < ActiveRecord
  encrypts :street, :city, :postal_code, :country, :phone_number, migrating: true
end
```
Notice last part of it - `migrating: true`. This is crucial for next step - migrate existing data. But before that I had to create new columns for encrypted data. So I came up with following migration:
```ruby
def up
  add_column :client_address, :street_ciphertext, :text
  add_column :client_address, :city_ciphertext, :text
  add_column :client_address, :postal_code, :text
  add_column :client_address, :country, :text
  add_column :client_address, :phone_number, :text

  change_column :client_address, :street, :string, null: true
  change_column :client_address, :city, :string, null: true
  change_column :client_address, :postal_code, :string, null: true
  change_column :client_address, :country, :string, null: true
  change_column :client_address, :phone_number, :string, null: true
end
```
At this point no `null: false` constraint could take place - adding `not_null` columns to existing records would paralyze app. Also `null: true` had to be added to existing columns - from now on we would save new records only to `_ciphertext` columns. 

After successful migration, there was only one thing missing. Data migration itself!
Thanks to Lockbox, this is done by running simple command in rails console. After merging above changes, I had to ssh to production environment and run
```ruby
Lockbox.migrate
```
At this point all existing data was migrated to `_ciphertext` columns. But I needed more - I needed to remove non-encrypted columns with sensitive data saved in plain text!

**Step II**
First of all I removed `migrating: true` from `models/client/address.rb` model - this was no longer needed.
Next thing was migration:
```ruby
def up
  change_column :client_address, :street, :text, null: false
  ...
end
```
For all `_ciphertext` columns I added `not_null` constraint, since we’re already saving records to that columns and none of them was empty anymore.
And the most important part of this pull request was adding `ignored_columns` to Address model. Since in next PR I wanted to remove all unnecessary columns this was crucial at to add this at this point.
```ruby
class Client::Address
  ...
  ignored_columns: %w[street city postal_code country phone_number]
  ...
end
```

**Step III**
This part is only about removing non-encrypted columns. So it included only this migration:
```ruby
def up
  remove_column :client_address, :street
  remove_column :client_address, :city
  remove_column :client_address, :postal_code
  remove_column :client_address, :country
  remove_column :client_address, :phone_number
end
```
Thanks to `ignored_columns` this could be deployed without causing any downtime to app. From this point there were no decrypted clients’ address data in our database.

Last step was to remove `ignored_columns` attribute from the `Address` model.

**Conclusion**
Encryption was definitely worth adding and considering fact that this update was deployed at Friday after 2a.m. with no issues, this shows that process is very easy.
At least on that set of data that I had to encrypt.