双语畅销书《艾伦图灵传》第5章:解谜接力赛(25)

The strength was that every message, after the first six letters, was enciphered on a different setting.

这样做的优点是，每个信息在开头六个字母之后，都是以不同的盘位设定进行编码的。

The weakness was that for one day, all the operators in the network would be using exactly the same state of the machine for the first six letters of their messages.

缺点是，在一天当中，整个通信网络中的每一条信息，开头的六个字母都是以完全相同的机器状态进行编码的。

Worse, those six letters always represented the encipherment of a repeated triplet.

更严重的是，这六个字母总是代表着两个相同的三位字母串。

It was this element of repetition that the Polish cryptanalysts were able to exploit.

正是这种重复的特性，被波兰的密码分析人员抓住了。

Their method was to collect each day, from their radio intercepts, a list of these initial six-letter sequences.

他们的方法是，每天从拦截到的所有无线电信息中，收集其开头六个字母，形成一份列表。

They knew that in this list, there would be a pattern.

他们知道，这个列表肯定有规律可循。

For if in one message the first letter were A, and the fourth letter was R, then in any other message where the first letter was A, the fourth letter would again be R.

如果在一条信息中，第一个字母是A，第四个字母是R，那么在其他信息中，只要第一位是A，那么第四位肯定也是R。

With enough messages, they could build up a complete table, say:

收集足够多的信息，就可以建立一个完整的表，比如：

First letter: 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

第一个字母：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

Fourth letter: R G Z L Y Q M J D X A O W V H N F B P C K I T S E U

第四个字母：R G Z L Y Q M J D X A O W V H N F B P C K I T S E U

There would be two further tables, connecting the second and fifth letters, and the third and sixth.

还有另外两个表，分别表示第二和第五个字母的关系，以及第三和第六个字母的关系。