book cover
From FLYNN's June 16, 1928


Edited by M. E. Ohaver
An Interesting Explanation Accompanies the Solution to the Le-
grand Open Letter Cipher of Last Week—With the Other Features

IN the year 1563 the Neapolitan physician, Giovanni Battista della Porta, published an important work on cryptography, wherein he describes what is reputed to be the first cipher devised to use a changeable key word, key phrase, or group of letters. An arrangement for the twenty-six-letter English alphabet of the table employed by this cipher is given herewith.

AB a b c d e f g h i j k l m
n o p q r s t u v w z y z
CD a b c d e f g h i j k l m
o p q r s t u v w x y z n
EF a b o d e f g h i j k l m
p q r s t u v w x y z n o
GH a b o d e f g h i j k l m
q r s t u v w x y i n o p
IJ a b c d e f g h i j k l m
r s t u v w x y z n o p q
KL a b o d e f g h i j k l m
s t u v w x y z n o p q r
MN a b o d e f g h i j k l m
t u v w x y z n o p q r s
OP a b o d e f g b i a k l m
u v w x y z n o p q r s t
QR a b o d e f g h i j k l m
v w x y z n o p q r s t u
ST a b c d e f g b i j k l m
w x y z n o p q r s t u t
UV a b c d e f g h i j k l m
x y a n o p q r s t u v w
WX a b o d e f g b i j k l m
y z a o p q r s t u v w x
YZ a b o d e f g h i j k l m
z n o p q r s t u v w x y

This cipher is a multiple alphabet system, the series of alphabets being controlled by means of the prearranged key. Each alphabet is provided with two key letters, either of which can be used to designate it. And any letter in any given alphabet is represented in cipher by the letter with which it is paired. In the first, or "A B" alphabet, for example, A is used for N, and N for A; B for O, and O for B; and so on.

The system is extremely easy to use. Thus to encipher (b), "Our plans are known," using the key word "Signet," merely write the key above the message, letter for letter, repeating it as many times as required, as shown at (a).

Then, using the cipher alphabets indicated by the key letters, find the substitute for each message letter in the manner described above. For e.xample, the substitute in the S-alphabet for O, the first letter of the message, is F, which accordingly becomes the first letter of the cryptogram.

Similarly, in the I-alphabet the substitute for U is D; and so on. The fully enciphered message is given at (c). Note that the first and last letters of the present key word, though different, control the same alphabet. Decipherment, of course, is merely a reversal of the process just described.


In its day the Porta cipher was thought to be absolutely indecipherable. As a matter of fact, however, the system can be resolved by a number of methods for this class of ciphers.

It is evident from the formation of the alphabets, for example, that any message letter and its equivalent cipher letter, or vice versa, must be in different halves of the alphabet. This makes it an easy matter to try the cipher for any desired words, and to rapidly eliminate those which do not meet the requirements.

Thus if it were suspected that OUR occurred in the above short example, QLT could at once be eliminated, since the only pair of letters in different halves of the alphabet would be U and L. Taking FDB as OUR would give three alphabets which could be tried at intervals in the cryptogram for probable translations. And if the assumption were correct decipherment would soon follow.

Now that you have full details of the Porta system, and some suggestions for solving it, turn to Cipher No. 187 in this issue.

This week's ciphers also include a clever crypt by J. Lloyd Hood, and a novel concealment cipher by David M. Raymond. The crypt is rather short, and for that reason may give you some trouble. In the null cipher, significant letters are interspersed with nonsignificants according to a numerical key.

Of last week's ciphers. No. 182, the crypt by M. Walker, conveyed the message: "Charitable organizations deprecate deplorable economic conditions among striking wheel-wrights." Comparison of the endings -LAUDN (-tions) and -ADS (-ing) gave nearly all the letters of the sixth and eighth words right off, making it easy to guess the rest.

No. 183, by Irving Bloom, used a straight A=1... Z=26 alphabet, with &=0. The numerical difference between each pair of cipher letters represented one letter of the message. Thus, NA (14 minus 1) equals M (13); TF (20 minus 5) equals O (15); and so on. The message in full: "More power to Flynn's, the most popular magazine published!"

The Legrand open letter cipher. No. 184, was prepared with the numerical key 1-9-1-6-2-5, derived from the word key SPY (S=19, P=16, Y=25). To decipher, number the words of the external letter with the ascending series 0-to-9, repeating as necessary.

Then mark the words indicated by the numerical key in the order in which they occur in the letter—as shown below in italics—and you will have the secret or internal message: "Have everything ready. Bank job will go through Monday." Did you get it?

 "We have not heard from Williams;
please wire when everything is ready.
Have deposited money in bank and can
start on the job at once.
 "Will hold ourselves in readiness to go
ahead pending receipt of wire. Can be
through by Monday if we start now."

Our.solvers' lists are coming along rather nicely now, but we would like to see more fans take an active interest. Whether you solve one or all, send in your answers from week to week. Answers to this week's ciphers will be published next week.

CIPHER No. 185, by J. Lloyd Hood, Bastrop, Texas.


CIPHER No. 186, by David M. Raymond, South Bend, Indiana.


CIPHER No. 187.