tags.  its a long tag.  if you enter the information separately, it'll resort to the smaller tags.  my encryption memory is rusty, so sorry if i butcher this.  its kinda like key pair encryption, where you combine two prime numbers (one public key and one private key) to get the master key.  if you try to reverse the master key, you'd have to use a super computer because it'd have to go through all the possibilities.  so its the combination of both the skew and src usa that makes the master key.