The following is much more ingenious, and difficult of detection.
+-----------------------------------+
| | A | B | C | D | E | F | G | H |
|---+---+---+---+---+---+---+---+---|
| A |_a_|_d_|_g_|_k_|_n_|_q_|_t_|_x_|
| | | | | | | | | |
| B |_b_|_e_|_h_|_l_|_o_|_r_|_u_|_y_|
| | | | | | | | | |
| C |_c_|_f_|_i_|_m_|_p_|_s_|_w_|_z_|
+-----------------------------------+
Now suppose that I want to write _England_; I look among the small letters
in the foregoing table for _e_, and find that it is in a horizontal line
with B, and vertical line with B, so I write down _B_B; _n_ is in line
with A and E, so I put AE; continue this, and England will be represented
by _Bbaeacbdaaaeab_. Two letters to represent one is not over-tedious: but
the scheme devised by Lord Bacon is clumsy enough. He represented every
letter by permutations of _a_ and _b_; for instance,
A was written _aaaaa_, B was written _aaaab_
C " " _aaaba_, D " " _aabaa_
and so through the alphabet. Paris would thus be transformed into _abbba,
aaaaa, baaaa, abaaa, baaab_. Conceive the labour of composing a whole
despatch like this, and the great likelihood of making blunders in writing
it!
A much simpler method is the following. The sender and receiver of the
communication must be agreed upon a certain book of a specified edition.
The despatch begins with a number; this indicates the page to which the
reader is to turn. He must then count the letters from the top of the
page, and give them their value numerically according to the order in
which they come; omitting those which are repeated. By these numbers he
reads his despatch. As an example, let us take the beginning of this
article: then, _I_ = 1, _n_ = 2, _w_ = 3, _h_ = 4, _e_ = 5, _m_ = 6, _d_ =
7, _l_ = 8, _o_ = 9, _u_ = 10, _v_ = 11, omitting to count the letters
which are repeated. In the middle of the communication the page may be
varied, and consequently the numerical significance of each letter
altered. Even this could be read with a little trouble; and the word
“impossible” can hardly be said to apply to the deciphering of
cryptographs.
A curious instance of this occurred at the close of the sixteenth century,
when the Spaniards were endeavouring to establish relations between the
scattered branches of their vast monarchy, which at that period embraced a
large portion of Italy, the Low Countries, the Philippines, and enormous
districts in the New World. They accordingly invented a cypher, which
they varied from time to time, in order to disconcert those who might
attempt to pry into the mysteries of their correspondence. The cypher,
composed of fifty signs, was of great value to them through all the
troubles of the “Ligue,” and the wars then desolating Europe. Some of
their despatches having been intercepted, Henry IV. handed them over to a
clever mathematician, Viete, with the request that he would find the clue.
He did so, and was able also to follow it as it varied, and France
profited for two years by his discovery. The court of Spain, disconcerted
at this, accused Viete before the Roman court as a sorcerer and in league
with the devil. This proceeding only gave rise to laughter and ridicule.
A still more remarkable instance is that of a German professor, Hermann,
who boasted, in 1752, that he had discovered a cryptograph absolutely
incapable of being deciphered, without the clue being given by him; and he
defied all the savants and learned societies of Europe to discover the
key. However, a French refugee, named Beguelin, managed after eight days’
study to read it. This cypher--though we have the rules upon which it is
formed before us--is to us perfectly unintelligible. It is grounded on
some changes of numbers and symbols; numbers vary, being at one time
multiplied, at another added, and become so complicated that the letter
_e_, which occurs nine times in the paragraph, is represented in eight
different ways; _n_ is used eight times, and has seven various signs.
Indeed the same letter is scarcely ever represented by the same figure;
but this is not all: the character which appears in the place of _i_ takes
that of _n_ shortly after; another symbol for _n_ stands also for _t_. How
any man could have solved the mystery of this cypher is astonishing.
Now let me recommend a far simpler system, and one which is very difficult
of detection. It consists of a combination of numbers and letters. Both
parties must be agreed on an arrangement such as that in the second line
below, for on it all depends.
1 2 3 4 5 6 7 8 9 10
4 7 2 9 1 10 5 3 6 8
Now in turning a sentence such as “The army must retire” into cypher, you
count the letters which make the sentence, and find that T is the first, H
the second, E the third, A the fourth, R the fifth, and so on. Then look
at the table. T is the first letter; 4 answers to 1; therefore write the
fourth letter in the place of T; that is A instead of T. For _h_ the
second, put the seventh, which is _y_; for E, take the second, _h_. The
sentence will stand “Ayh utsr emma yhutsr.” It is all but impossible to
discover this cypher.
All these cryptographs consist in the exchange of numbers or characters
for the real letters; but there are other methods quite as intricate,
which dispense with them.
The mysterious cards of the Count de Vergennes are an instance. De
Vergennes was Minister of Foreign Affairs under Louis XVI., and he made
use of cards of a peculiar nature in his relations with the diplomatic
agents of France. These cards were used in letters of recommendation or
passports which were given to strangers about to enter France; they were
intended to furnish information without the knowledge of the bearers. This
was the system. The card given to a man contained only a few words, such
as: