He used a black hat to pass secret messages.

他用一顶黑帽子来传递隐秘的信息。

youdao

Did you ever discuss codes, or any means of passing secret messages, with Dumbledore?

你跟邓布利多谈论过密码和传递秘密情报的其他方式吗？

youdao

Uncle Vernon: Harumph. So you can send secret messages to your 2 freaking little friends?

弗农姨父：哼，好让它给你那群变态小朋友通风报信吗？

youdao

It's a secret number so that if Julius Caesar scrambled his message with the key 13, well, then the recipient had better know what that number is or realistically, -- and this is why it's kind of hard to buy -- into some of these age old algorithms, -- what would an alternative approach be to figuring out Julius Caesar's messages to his generals if he didn't know that secret number was 13?

它是一个机密的数字，以至于,如果凯撒大帝使用密钥13加密了它的消息，然后接收者最好知道那个数字是什么,实际上--这就是为什么很难,破解这些古老的算法-,有什么变换方法使凯撒大帝的将军,可以解密凯撒大帝的消息，如果他不知道,那个机密数字是13呢？

哈佛公开课 - 计算机科学课程节选

Among the tricks of the spy trade the book reportedly reveals is MI6's accidentally discovered method of transferring secret messages.

BBC: Spy tactics revealed by book

Research groups in the U.S., Europe and Canada devised ways to use DNA to encode trademarks and secret messages in cells.

WSJ: Harvard Researchers Turn Book Into DNA Code

As the centre of Muslim pilgrimage, Saudi Arabia will always be a place for extremists from across the world to meet and plot, sometimes carrying secret messages.

ECONOMIST: A survey of al-Qaeda