>> these metal tags could be of four different shapes. the guard would write the number of the metal tag onto the paper pass and file it away, and then give her that tag. >> then i go to checkpoint four, the double gate. and i show the tag to get in the dorm. when i leave the dorm, i have to show the tag again. >> at checkpoint three, she would present a tag to the guard. he would go into his file of paper receipts and find the one that he had written that number on and he would hand it back to her. >> at checkpoint two, i hand back the pass to the guard who filled it out. >> he would then confirm that was his signature. >> so we need perfect copies of the pass. in all eight colors and be able to forge the guard's signature.