CODE MESSAGE TRANSMITTING MONEY TO SIR ROGER CASEMENT
In English it reads: “Embassy. 307–16, New York, April 10, 1916. Mr. John Devoy has paid in $500 here with the request that they be transmitted telegraphically to Sir Roger Casement. You are respectfully requested to proceed accordingly and to charge the amount to the Military Information Bureau. Receipt enclosed.”
Messages of that sort could be exchanged daily between a broker in Wall Street and a broker in Amsterdam, and, by the addition of a few more words, could be infinitely varied and would look like perfectly legitimate commercial correspondence. In fact, most international business before the war (the Government now requires that all messages appear in plain English) was carried on by coded cables which turned long messages into short groups of words that of themselves made gibberish. Several code books for business use were on the market, containing hundreds of pages of these arbitrary substitutions, which were useful, not for secrecy but for economy. A dozen words could be made to say what normally would require five hundred words.
Ciphers, however, have almost always been resorted to when secrecy was desired. This sounds like a contradiction. But people who are not experts use them because they think they are more secret, since they look so. And experts use them when they are concerned only with temporary secrecy. They use them, then, because cipher messages can be written and translated (by one’s correspondent) without any equipment, like a code book, and much more rapidly than code. Thus, if a general in the field wishes to send a message ordering a colonel to advance in two hours, he sends it in cipher, because it would take the enemy more than two hours to decipher the message even if he intercepted it immediately, and because after the two hours have elapsed the information in the message would be of no value to him.
A cipher is the substitution of some symbol for a letter of the alphabet. The substituted symbol may be another letter—as writing e when you mean a. Or it may be a figure—as using 42 when you mean m. Or it may be an arbitrary sign—as * to mean c. In cipher, then, every word is spelled out, but the word Washington might be spelled x=‖½?!^:°B if you had agreed that
| w = x | n = ! |
| a = = | g = ^ |
| s = ‖ | t = : |
| h = ½ | o = ° |
| i = ? | n = B |
That is called a substitution cipher, because some other letter or symbol is arbitrarily substituted for every letter.
But another kind is called a transposition cipher, because in this the letters of the alphabet are simply transposed by agreement—the simplest and most obvious example being to reverse the alphabet, so that z stands for a and y for b, etc. Such a transposition cipher would read: