def verify(sig, signed_text = nil, plain = Data.new)
      err = GPGME::gpgme_op_verify(self, sig, signed_text, plain)
      exc = GPGME::error_to_exception(err)
      raise exc if exc
      plain
    end
def verify(sig, signed_text = nil, plain = Data.new)
      err = GPGME::gpgme_op_verify(self, sig, signed_text, plain)
      exc = GPGME::error_to_exception(err)
      raise exc if exc
      plain
    end
Verify that the signature in the data object is a valid signature.