The Case of the Suspicious Sandwich
Let’s suppose that you leave your sandwich open on your desk when you go over to the fax machine to pick up an important fax. When you come back, you feel somehow that the sandwich has shifted a little to the left. Has someone tampered with your sandwich, perhaps placing some barbiturate in it to knock you out so that he can steal your cool new wireless mouse? Or perhaps he’s after the PL/SQL book hidden in your drawer? Maybe it’s not drugs, but sand, in your sandwich? The possibilities spin madly through your mind, and you lose your appetite.
To calm your fears, you decide to challenge the integrity of the sandwich. Being the careful fellow you are, you had previously weighed the sandwich and recorded its weight out to the 10th digit after the decimal point. Confronted with the possibility of an altered sandwich, you weigh it again and compare the results. They are exactly the same, down to that 10th digit of precision.What a relief! If someone had actually changed the sandwich in any way—for example, by adding barbiturates or sand—the weights would have been different, thus revealing the adulteration.
Pay close attention to the concepts presented here. You did not “hide” the sandwich (i.e., encrypt it); you simply created your own method of calculating a value that represents the sandwich. You could then compare the before and after values. The value you arrived at could have been based on any algorithm—in this case, it was the weight of the sandwich. ...