雙語暢銷書《艾倫圖靈傳》第5章:解謎接力賽(5)
They established themselves in the stables building of the mansion, soon dubbed 'the Cottage', and developed the ideas that the Poles had supplied at the eleventh hour.
There was no glaMour about ciphers. In 1939 the job of any cipher clerk, although not without skill, was dull and monotonous.
密碼本身沒有什麼樂趣，在1939年，密碼工作是非常枯燥乏味的，但它是無線電通信的必要環節。But ciphering was the necessary consequence of radio communication.
無線電廣泛用於空、海、和機動的陸地工事。
Radio had to be used for aerial, naval, and mobile land warfare, and a radio message to one was a message to all.
一個無線電信息發射出去，可以被所有方向接收，所以必須對信息進行加密。So messages had to be disguised, and not just this or that 'secret message', as with spies and smugglers, but the whole communication system.
不光是間諜或其它機密信息需要加密，整個通信系統的所有信息都需要加密。It meant mistakes, restrictions, and hours of laborious work on each message, but there was no choice.
這就意味着漏洞和限制，還有極大的工作量，但是他們別無選擇。The ciphers used in the 1930s did not depend on any great mathematical sophistication, but on the simple ideas of adding on and substituting.
30年代的密碼技術並不依賴數學技巧，只是一些基本的疊加和替換。The 'adding on' idea was hardly new; Julius Caesar had concealed his communications from the Gauls by a process of adding on three to each letter, so that an A became D, a B became an E, and so on.
疊加並不是個新穎的想法，朱利葉斯·凱撒就通過把字母疊加3位，使A變成D、B變成E等等，使他的通信無法被高盧人理解。More precisely, this kind of adding was what mathematicians called 'modular' addition, or addition without carrying, because it meant Y becoming B, Z becoming C, as though the letters were arranged around a circle.
準確地說，這種疊加就是數學上講的模加，也就是無進位加法，因爲它將Y變成B、Z變成C，就好比把字母排成了一個圓圈。Two thousand years later, the idea of modular addition by a fixed number would hardly be adequate, but there was nothing out-of-date about the general idea.
在凱撒時代遠去2000年之後，固定數字的模加，已經很難滿足需要了，但這個基本思路並沒過時。
