a laborious business, and the kind of thing I have always been bad at.
这是非常吃力的工作，这类工作是我最不擅长的。
First, one had to subtract from the groups of numbers in the telegram corresponding groups from a so-called one-time pad;
首先，要取一张一次性的密钥纸，将电报中的很多组数字，减掉密钥纸上对应的数字，
then to look up what the resultant groups signified in the code book.
首先，要取一张一次性的密钥纸，将电报中的很多组数字，减掉密钥纸上对应的数字，
Any mistake in the subtraction, or, even worse, in the groups subtracted, threw the whole thing out.
在相减的过程中，一旦出了任何差错，就会全部前功尽弃。
I toiled away at it, getting into terrible muddles and having to begin again…
我废寝忘食地做着这项工作，但却不断地陷入可怕的混乱，然后又要从头开始……
Alternatively, a cipher system might be based upon the 'substitution' idea.
在相减的过程中，一旦出了任何差错，就会全部前功尽弃。
In its simplest form, this was used for puzzle-page cryptograms, such as they had solved in Princeton treasure hunts.
在相减的过程中，一旦出了任何差错，就会全部前功尽弃。
It meant that one letter of the alphabet would be substituted for another, according to some fixed rule like:
这种方法就是，将字母表中的字母，按照特定的规则进行替换，比如：
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
K S G J T D A Y O B X H E P W M I Q C V N R F Z U L
K S G J T D A Y O B X H E P W M I Q C V N R F Z U L
so that TURING would become VNQOPA.
根据这个规则，TURING加密后就变成了VNQOPA。
Such a simple, or 'mono-alphabetic' cipher could easily be solved by looking at letter frequencies, common words, and so forth, and in fact the only point of puzzle-page problems was that the setter would include peculiar words like XERXES to make this difficult.
但是，这样一个简单的、单字母的替换规则，只要通过观察字母的频率、相同字母的规律等等，就可以很容易地破解。在普林斯顿的寻宝游戏中，艾伦他们通过设计一些XERXES之类的古怪词语，来增加破解的难度，
Such a system would be too simple-minded for military application.
但这样的系统对于军事应用来说，实在是过于幼稚了。
But there were systems in use in 1939 which were not much more advanced.
不过，1939年使用的某些系统，并没比这先进到哪里去。
One sophistication lay in the use of several alphabetic substitutions, used in rotation or according to some other simple scheme.
某些字母替换系统，使用了一些技巧，比如说轮流使用多套规则。