# Gemfile
  gem 'attr_encrypted'

# bash
  rails g migration add_message_to_users encrypted_message

# user.rb
  attr_encrypted :message, key: 'a secret key'

  <%= simple_form_for(@user) do |f| %>
    <%= f.error_notification %>

    <div class="form-inputs">
      <%= f.input :first_name %>
      <%= f.input :last_name %>
      <%= f.input :message %>
    </div>

    <div class="form-actions">
      <%= f.button :submit %>
    </div>
  <% end %>