雙語暢銷書《艾倫圖靈傳》第5章:解謎接力賽(9)

The few manuals and text-books3 of cryptology in existence devoted themselves mainly to such 'poly-alphabetic' ciphers.

當時的一些講授密碼學的資料或教材，主要都是講這種字母替換法。

Slightly more complex was the use of a system which substituted not for single letters, but for the 676 possible letter pairs.

某些字母替換系統，使用了一些技巧，比如說輪流使用多套規則。

One British cipher system of this period was of this nature, combining the idea with the use of a code book. It was used by the Merchant Navy.4

當時英國有一種密碼系統，就是這種類型的，與密碼手冊配套使用。英國商船隊使用的就是這樣的系統。

The cipher clerk would first have to render the message into Merchant Navy Code, thus:

密碼操作員首先要把信息翻譯成商船通信碼，比如：

Text Coded, Expect to arrive at VQUW, 14, CFUD, 40 UQGL

信息通信碼，預計到達時間VQUW，14 CFUD，40 UQGL

The next step required an even number of rows, so the clerk would have to add a nonsense word to make it up:Balloon ZJVY

下一步需要將行數變成偶數，因此操作員可能會添上一個沒有意義的詞，比如：氣球ZJVY。

Then the encipherment would be done.

然後就可以進行編碼。

The clerk would take the first vertical pair of letters, here VC, and look it up in a table of letter pairs.

操作員先取出縱向的第一對字母，在這裏就是VC，然後在替換表中找到對應的替換。

The table would specify some other pair, say XX.

這張表包括了所有的XX這樣的字母對。

The clerk would continue to go through the message, substituting for each letter pair in this way.

操作員重複這個過程，對每一對字母進行替換。

There was little more to it, except that as with the 'adding on' kind of cipher, the process was futile unless the legitimate receiver knew which substitution table was being used.

其它就沒什麼特別的，與疊加型的密碼一樣，接收者必須知道使用的是哪個替換表，否則就無法解密信息。

To preface the transmission with 'Table number 8', say, would allow the enemy analyst to collect and collate the transmissions enciphered with the same table, and make an attack.

然而，如果在通信中說出來"使用8號表"，那麼敵方分析員就會將使用同一張表的信息蒐集到一起，尋找規律進行破解。

There had to be some element of disguise involved.

因此，還要再做一些僞裝工作。