密码学是关于在存在对手的情况下进行通信的。

性格是一个人习惯的总和。

写过去是理解现在和想象不同未来的一种方式。

释义：人生活在宇宙之间，就像蜗牛争斗、蚊虫追逐飞鸟一样微不足道。

At that age， I'd take any excuse to make estimates and do minor arithmetic. I'd calculate our gas mileage -- figure out useless statistics on things like grocery spending. I'd been hearing an ad campaign about smoking. I can't remember the details， but basically the ad said， every puff of a cigarette takes some number of minutes off of your life: I think it might have been two minutes per puff. At any rate， I decided to do the math for my grandmother. I estimated the number of cigarettes per days， estimated the number of puffs per cigarette and so on. When I was satisfied that I'd come up with a reasonable number， I poked my head into the front of the car， tapped my grandmother on the shoulder， and proudly proclaimed， "At two minutes per puff， you've taken nine years off your life！"