But the point is that how is Facebook, how is Amazon possibly going to communicate securely with you or your laptop using cryptology if you both have to know the same secrets.

关键是Facebook是怎么样，亚马逊是怎么样安全地和你或你的计算机,使用加密技术进行交流的，如果你们两个都,知道那个同样的密钥。

哈佛公开课 - 计算机科学课程节选