Dear sir:
I should perhaps apologise for again intruding a subject upon which you have so ably commented, and which may be supposed by this time to have been almost exhausted; but as I have been greatly interested in the articles upon “cryptography,” which have appeared in your Magazine, I think that you will excuse the present intrusion of a few remarks. With secret writing I have been practically conversant for several years, and I have found, both in correspondence and in the preservation of private memoranda, the frequent benefit of its peculiar virtues. I have thus a record of thoughts, feelings and occurrences,—a history of my mental existence, to which I may turn, and in imagination, retrace former pleasures, and again live through by-gone scenes,—secure in the conviction that the magic scroll has a tale for my eye alone. Who has not longed for such a confidante?
Cryptography is, indeed, not only a topic of mere curiosity, but is of general interest, as furnishing an excellent exercise for mental discipline, and of high practical importance on various occasions;—to the statesman and the general—to the scholar and the traveller,—and, may I not add “last though not least,” to the lover? What can be so delightful amid the trials of absent lovers, as a secret intercourse between them of their hopes and fears,—safe from the prying eyes of some old aunt, or it may be, of a perverse and cruel guardian?—a billet doux that will not betray its mission, even if intercepted, and that can “tell no tales” if lost, or, (which sometimes occurs,) if stolen from its violated depository.
In the solution of the various ciphers which have been submitted to your examination, you have exhibited a power of analytical and synthetical reasoning I have never seen equalled; and the astonishing skill you have displayed,—particularly in deciphering the cryptograph of Dr. Charles J. Frailey, will, I think, crown you the king of “secret-readers.” But notwithstanding this, I think your opinion that the construction of a real cryptograph is impossible, not sufficiently supported. Those examples which you have published have indeed not been of that character, as you have fully proved. They have, moreover, not been sufficiently accurate, for where the key was a phrase, (and consequently the same character was employed for several letters,) different words would be formed with the same ciphers. The sense could then only be ascertained from the context, and this would amount to a probability—generally of a high degree, I admit—but still not to a positive certainly. Nay, a case might readily be imagined, where the most important word of the communication, and one on which the sense of the whole depended, should have so equivocal a nature, that the person for whose benefit it was intended, would be unable, even with the aid of his key, to discover which of two very different interpretations should be the correct one. If necessary, this can easily be shown; thus, for example, suppose a lady should receive from her affianced, a letter written in ciphers, containing this sentence, “4 5663 967 268 26 3633,” and that a and n were represented by the figure 2,—e, m, and r by 3,—i by 4,—l by 5,—o, s, and v by 6,—u by 7,—w by 8,—and y by 9; a moment’s inspection will show that the sentence might either be “I love you now as ever,” or “I love you now no more.” How “positively shocking,” “to say the least of it;” and yet several of the ciphers that you have published, have required a greater number of letters to be represented by one character, than any to be found in the example before us. It is evident, then, that this is not a very desirable system, as it would scarcely be more useful than a lock without its key, or with one that did not fit its wards.
I think, however, that there are various methods by which a hieroglyphic might be formed, whose meaning would be perfectly “hidden;” and I shall give one or two examples of what I consider such. A method which I have adopted for my own private use, is one which I am satisfied is of this nature, as it cannot possibly be solved without the assistance of its key, and that key, by which alone it can be unlocked, exists only in my mind; at the same time it is so simple, that with the practice in it which I have had, I now read it, and write it, with as much facility as I can the English character. As I prefer not giving it here, I shall be compelled to have recourse to some other plan that is more complicated. By a CRYPTOGRAPH, I understand—a communication which, though clearly ascertained by means of its proper key, cannot possibly be without it. To most persons, who have not thought much upon the subject, an article written in simple cipher, (by which I mean with each letter uniformly represented by a single distinct character,) would appear to be an impenetrable mystery; and they would doubtless imagine that the more complicated the method of constructing such a cipher, the more insoluble—to use a chemical expression—would be the puzzle, since so much less would be the chance of discovering its key. This very natural conclusion is, however, erroneous, as it is founded on the supposition that possession must first be obtained of the key, in order to unravel the difficulty,—which is not the case. The process of reasoning employed in resolving “secret writing” has not the slightest relation to the form or description of the characters used, but refers simply to their succession, and to a comparison of words in which the same letters occur. By these means any cipher of this nature can be unriddled, as experience has fully shown. A very successful method of avoiding detection, would be to apply the simple cipher to words written backwards and continuously. This, I conceive, might be called a perfect cryptograph, since from the want of spaces, and consequently the impossibility of comparing words, it would utterly perplex the person attempting to discover its hidden import, and yet with the help of the key, each letter being known, the words could easily be separated and inverted. I give a short specimen of this style, and would feel much gratified with your opinion of the possibility of reading it.
Should this not be considered perfect, (though I suspect it would puzzle even the ingenious editor to detect its meaning,) I shall give another method below, which I can show must be, and if I am successful I think you will do me the justice to admit that “human ingenuity” has contrived “a cipher which human ingenuity cannot resolve.” I wish to be distinctly understood; the secret communication above, and the one following, are not intended to show that you have promised more than you can perform. I do not take up the gauntlet. Your challenge, I am happy to testify, has been more than amply redeemed. It is merely with an incidental remark of yours, that I am at present engaged, and my object is to show that however correct it may be generally,—it is not so universally.
Agreeably to a part of my foregoing definition, that cannot be a proper cryptograph, in which a single character is made to represent more than one letter. Let us for a moment see what would be the result if this was reversed,—that is, if more than one cipher were used for a single letter. In case each letter were represented by two different characters, (used alternately or at random,) it is evident that while the certainty of reading such a composition correctly, by help of the key, would not be at all diminished, the difficulty of its solution without that help, would be vastly increased. This then is an approach to the formation of a secret cipher. If, now, the number of the characters were extended to three or four for each letter, it might be pronounced with tolerable certainty that such a writing would be “secret.” Or, to take an extreme case, a communication might be made, in which no two characters would be alike! Here all reasoning would be entirely baffled, as there would evidently be no objects of comparison; and even if half a dozen words were known, they would furnish no clue to the rest. Here, then, is a complete non plus to investigation, and we have arrived at a perfect cryptograph. For, since any given cipher would stand for but one letter in the key, there could be but a single and definite solution; and thus both conditions of my definition are fully satisfied. In the following specimen of this method, I have employed the Roman-capital, small letter, and small capital, with their several inversions, giving me the command of 130 characters, or an average of five to each letter. This is to “make assurance doubly sure,” for I am satisfied that were an average of three characters used for each letter, such a writing would be emphatically secret. If you will be so kind as to give my cipher a place in your interesting Magazine, I will immediately forward you its key. Hoping that you will not be displeased with my tedious letter,
I am most respectfully yours.
W. B. TYLER.