雙語暢銷書《艾倫圖靈傳》第5章:解謎接力賽(6)

One important type of cipher used the idea of 'modular addition', but instead of fixed number, it would be a varying sequence of numbers, forming a key, that would be added to the message.

有一種很重要的密碼技術，仍然使用模加的想法，但它不是使用固定數字，而是用一個變化的數列形成密鑰，然後疊加到信息中。

In practice, the words of the message would first be encoded into numerals by means of a standard code-book.

在實踐中，首先會根據標準密碼手冊，把一個消息中的單詞全部編碼成數字。

The job of the cipher clerk would then be to take this 'plain-text', say

然後，密碼人員的工作，就是將這些明文，比如

6728 5630 8923，

6728 5630 8923,

9620 6745 2397，

9620 6745 2397,

5348 1375 0210

5348 1375 0210

by modular addition.

與一組密鑰進行模加，得到一個密文。

For this to be of any use, however, the legitimate receiver had to know what the key was, so that it could be subtracted and the 'plain-text' retrieved.

要想讀取這組信息，接收方必須知道密鑰是什麼，然後才能對密文進行正確的模減，得到原始的明文。

There had to be some system, by which the 'key' was agreed in advance between sender and receiver.

所以需要有一種系統，事先在發送方和接受方之間，生成統一的密鑰。