THE detective work accomplished by the United States Government
since its entry into the war has been worthy of a Sherlock Holmes,
and yet few persons, reading only the results of this remarkably
developed system, have realized that a Government heretofore finding
it unnecessary to match wits with foreign spy bureaus has suddenly
taken a high rank in this unpleasant but absolutely essential branch of
war-making—as it has in all others. The public read of the intercepted
dispatches from the Argentine to Germany by way of Sweden, and of the
Bernstorff messages, but without a realization of the problem that a
cipher dispatch presents to one who has not the key. And probably the
average reader is unaware that, in both the army and navy, experts
have been trained to decipher code messages, with the result that both
the making and the reading of such dispatches have been reduced to an
almost mathematical science. The Philadelphia _Press_, in outlining the
instruction given in this important work at the Army Service schools,
says:
What is taught the military will furnish an idea of the task of the
code experts in the State Department, and of the basis of the science
that has unmasked the German plans with respect to vessels to be
_spurlos versenkt_ and of legislators to be influenced through the
power of German gold.
“It may as well be stated,” says Capt. Parker Hitt—that is, he was
a captain of infantry when he said it—“that no practicable military
cipher is mathematically indecipherable if intercepted; the most
that can be expected is to delay for a longer or shorter time the
deciphering of the message by the interceptor.”
The young officer is warned that one doesn’t have to rely in these
times upon capturing messengers as they speed by horse from post to
post. All radio messages may be picked up by every operator within the
zone, and the interesting information is given that if one can run a
fine wire within one hundred feet of a buzzer line or within thirty
feet of a telegraph line, whatever tidings may be going over these
mediums may be copied by induction.
In order that the student may not lose heart, it is pointed out in the
beginning that many European powers use ciphers that vary from extreme
simplicity to “a complexity which is more apparent than real.” And as
to amateurs, who make up ciphers for some special purpose, it’s dollars
to doughnuts that their messages will be read just as easily as though
they had printed them in box-car letters.
At every headquarters of an army the intelligence department of the
General Staff stands ready to play checkers with any formidable looking
document that comes along in cipher, and there is mighty little matter
in code that stands a ghost of a chance of getting by.
The scientific dissection of ciphers starts with the examination of
the general system of language communication, which, with everybody
excepting friend Chinaman, is an alphabet composed of letters that
appear in conventional order.
It was early found by the keen-eyed gentlemen who analyzed ciphers that
if one took ten thousand words of any language and counted the letters
in them the number of times that any one letter would recur would be
found practically identical with their recurrence in any other ten
thousand words. From this discovery the experts made frequency tables,
which show just how many times one may expect to find a letter e or any
other letter in a given number of words or letters. These tables were
made for ten thousand letters and for two hundred letters, so that one
might get an idea how often to expect to find given letters in both
long and short messages or documents.
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: