If you have some plain text, some message that you want to send, well, you can encrypt it or you can scramble it using a key, a secret key, which might be a physical machine like the Enigma 13 or it might be a number like 13.

如果你有没有加密的文本，你想要寄送的一些消息,你就可以加密它,或者你可以用一个密钥使其变得混乱，那就像一个英格玛的物理装置,或者他就是一个数字。

哈佛公开课 - 计算机科学课程节选

You type at the keyboard words that you want to encrypt.

你从键盘上键入你想加密的单词。

哈佛公开课 - 计算机科学课程节选

But how many of you have ever called Facebook up or called Amazon up and kind of whispered into their ear I'm going to encrypt this with the number 13.

但是有谁听过Facebook或者亚马逊,稍微低声地告诉他们,我将用密钥13加密这个消息？

哈佛公开课 - 计算机科学课程节选