Must provide a high level of security. Must be easy to understand. Must be exportable. Must be available to all users. To sum it up DES is the official government encryption program and is used to send vital, confidential, or secret information to another party.
Lets take a look at a post card.
You want to send a postcard to a good friend from Hawaii. So you pick one up from the local gift shop and write a short message on the back and send it off. Your post card will probably go through three or four post offices, being directly handled by over 10 postal clerks. If it is a slow day or your post card peaks their interest they may just turn it around and get a kick out of it. This is how most transactions over the Internet act.