An authentication method includes determining that a unique overt identifier is associated with a product; detecting that a random covert identifier is associated with the product, wherein the covert identifier includes at least one taggant particle, the unique overt identifier is combined with the random covert identifier, and the unique overt identifier is not a function of the random covert identifier; and comparing the unique overt identifier and the random covert identifier respectively to a unique overt number and a random covert number stored in a database.