Best way to store bank account information of users?

app-models-user.rb

#file name and path   app/models/user.rb


class User
  attr_encrypted :bank_account_number, key: ENV['salt']
end

config-application.rb

#file name and path   config/application.rb

require File.expand_path('../boot', __FILE__)

require 'rails/all'

Bundler.require(*Rails.groups)

module ProjectName
  class Application < Rails::Application
    config.active_record.raise_in_transactional_callbacks = true

    config.before_initialize do
      dev = File.join(Rails.root, 'config', 'config.yml')
      YAML.load(File.open(dev)).each do |key,value|
      ENV[key.to_s] = value
      end if File.exists?(dev)
    end
  end
end

config-config.yml

#file name and path   config/config.yml
# var section 

salt: 'This is a key that is 256 bits!!'