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

If you just scramble a sentence, it's pretty useless because the recipients are never going to be able to reverse the process.

如果你只是加密一个句子，这是毫无用处的,因为收件人没法将这个句子,反加密出来。

哈佛公开课 - 计算机科学课程节选