# File lib/devise_two_factor/models/two_factor_backupable.rb, line 17
      def generate_otp_backup_codes!
        codes           = []
        number_of_codes = self.class.otp_number_of_backup_codes
        code_length     = self.class.otp_backup_code_length

        number_of_codes.times do
          codes << SecureRandom.hex(code_length / 2) # Hexstring has length 2*n
        end

        hashed_codes = codes.map { |code| Devise::Encryptor.digest(self.class, code) }
        self.otp_backup_codes = hashed_codes

        codes
      end