def initialize(policy = {}, opt = {})
      # set options
      @opt = Gem::Security::OPT.merge(opt)

      # build policy
      policy.each_pair do |key, val|
        case key
        when :verify_data   then @verify_data   = val
        when :verify_signer then @verify_signer = val
        when :verify_chain  then @verify_chain  = val
        when :verify_root   then @verify_root   = val
        when :only_trusted  then @only_trusted  = val
        when :only_signed   then @only_signed   = val
        end
      end
    end
Create a new Gem::Security::Policy object with the given mode and
options.