Thus we find the following result:
| Letters | ||
|---|---|---|
| 10000 | 200 | |
| A | 778 | 16 |
| B | 141 | 3 |
| C | 296 | 6 |
| D | 402 | 8 |
| E | 1277 | 26 |
| F | 197 | 4 |
| G | 174 | 3 |
| H | 595 | 12 |
| I | 667 | 13 |
| J | 51 | 1 |
| K | 74 | 2 |
| L | 372 | 7 |
| M | 288 | 6 |
| N | 686 | 14 |
| O | 807 | 16 |
| P | 223 | 4 |
| Q | 8 | .. |
| R | 651 | 13 |
| S | 622 | 12 |
| T | 855 | 17 |
| U | 308 | 6 |
| V | 112 | 2 |
| W | 176 | 3 |
| X | 27 | .. |
| Y | 196 | 4 |
| Z | 17 | .. |
It is found that in any text the vowels A E I O U represent 38.37 per cent; that the consonants L N R S T represent 31.86 per cent, and that the consonants J K Q X Z stand for only 1.77 per cent. One doesn’t want to shy away from these figures as being dry and dull, because they form part of a story as interesting as any detective narrative that was ever penned by a Conan Doyle.
For the usual purposes of figuring a cipher the first group is given the value of 40 per cent, the second group 30 per cent, and the last 2 per cent. And then one is introduced to the order of frequency in which letters appear in ordinary text. It is:
E T O A N I R S H D L U C M P F Y W G B V K J X Z Q.
Tables are then made for kinds of matter that is not ordinary, taken from various kinds of telegraphic and other documents, which will alter only slightly the percentage values of the letters as shown in a table from ordinary English.
Having gone along thus far, the expert figures how many times he can expect to find two letters occurring together. These are called digraphs, and one learns that AH will show up once in a thousand letters, while HA will be found twenty-six times. These double-letter combinations form a separate table all of their own, and the common ones are set aside, as TH, ER, ON, OR, etc., so they can be readily guessed or mathematically figured against any text.
Tables of frequency are figured out for the various languages, particularly German, and the ciphers are divided into two chief classes, substitution and transposition. The writer in The Press says:
Now you will remember those percentages of vowels and consonants. Here is where they come in. When a message is picked up the army expert counts the times that the vowels recur, and if they do not check with the 40 per cent for the common vowels, with the consonant figures tallying within 5 per cent of the key, he knows that he is up against a substitution cipher. The transposition kind will check to a gnat’s heel.
When the expert knows exactly what he is up against he is ready to apply the figures and patiently unravel the story. It may take him hours, and maybe days, but sooner or later he will get it to a certainty.