manyfold/app/models/altcha_solution.rb

class AltchaSolution < ApplicationRecord
  validates :algorithm, :challenge, :salt, :signature, :number, presence: true
  attr_accessor :took

  def self.verify_and_save(base64encoded)
    p = begin
      JSON.parse(Base64.decode64(base64encoded))
    rescue
      nil
    end
    return false if p.nil?

    submission = Altcha::Submission.new(p)
    return false unless submission.valid?

    solution = new(p)

    begin
      solution.save
    rescue ActiveRecord::RecordNotUnique
      # Replay attack
      false
    end
  end

  def self.cleanup
    # Replay attacks are protected by the time stamp in the salt of the challenge for
    # the duration configured in the timeout. All solutions in the database that older
    # can be deleted.
    AltchaSolution.where(created_at: ...(Time.zone.now - Altcha.timeout)).delete_all # rubocop:disable Pundit/UsePolicyScope
  end
end