Bob and Alice are quite closely friends. They are both intersted on Researching ciper. As everybody knows , they ,of course, are experienced computer users. So they always communicate their new reaserches on ciyper by Internet. But now, unfortunetly, their country is suffering from a cruel war caused by nucleus. However the enemy state is so powerful much more than their motherland. So after several months Bob and Alice's country is controled by enemy on many areas, including network. Any communications on the network are highly suspiciously. If anybody uncareful,he may lost his life! This situation is so dangerious to computer users. So Bob's mother and Alice's father make a decision together for their childern --- forbid them to use computer again. Bob and Alice can't disobey this dicesion ,but they also don't want to pause their new research. So they also make a decison together -
