Colonel A---- (the reader will learn why I give neither his name nor
real rank) spoke with some bitterness of the inquisitiveness which
rendered it impossible, he said, to trust an American with a secret,
and very difficult to keep one without lying. We were presently joined
by Major B----, who had been employed during the war in the conduct of
many critical communications, and had shown great ingenuity in
devising and unravelling ciphers. On this subject a somewhat
protracted discussion arose. I inclined to the doctrine of Poe, that
no cipher can be devised which cannot be detected by an experienced
hand; my friends indicated simple methods of defeating the processes
on which decipherers rely.
"Poe's theory," said the Major, "depends upon the frequent recurrence
of certain letters, syllables, and brief words in any given language;
for instance, of _e_'s and _t_'s, _tion_ and _ed_, _a_, _and_, and
_the_ in English. Now it is perfectly easy to introduce abbreviations
for each of the common short words and terminations, and equally easy
to baffle the decipherer's reliance thereon by inserting meaningless
symbols to separate the words; by employing two signs for a common
letter, or so arranging your cipher that no one shall without extreme
difficulty know which marks stand for single and which for several
combined letters, where one letter ends and another begins.
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