THE Porta cipher, which has been discussed in the last two issues, is famous not only in being the first cipher to employ a changeable key word, but also in the fact that it has been used by some of the world's greatest celebrities.
For example, it was one of the ciphers used by Napoleon I; and a slightly modified form of the'table, in which the alphabets were less systematic in their structure, was used in Elizabethan state correspondence with Spain.
In view of these facts our readers will no doubt be interested to learn that this famous system can also be arranged for use as a simple machine cipher, employing a sliding alphabet something like that used in the St. Cyr variation of the Vigencre cipher square.
The apparatus for the Porta cipher, as illustrated herewith, can be prepared in a few minutes on the typewriter or by hand. The rectangular card bearing the A-to-M half of the alphabet is provided with two transverse slits which permit the strip bearing the N-to-Z half of the alphabet to be adjusted to any desired key letter.
┌───────────────────────────────┐
│ (alphabet) │
│ A B C D E F G H I J K L M │
┌─────────┤ ├─────────────────────────┤ ├─────────┐
│ N O P Q│ │T U V W X Y Z N O P Q R S│ │V W X Y │
│ │ │ │ │ │
│ A C E G│ │M O Q S U W Y │ │ │
│ B D F H│ │N P R T V X Z │ │ │
└─────────┤ ├─────────────────────────┤ ├─────────┘
│ *(key letter) │
│ │
└───────────────────────────────┘
As in the tabular form of the cipher, each cipher alphabet here also can be indicated by either of two key letters. The illustration shows the "M" or "N" alphabet in position. In this alphabet A is represented by T, and T by A; B by U, and U by B; and so on. Each of the thirteen alphabets is used in the same way.
Last week's Porta Cipher No. 190 will serve to demonstrate the method of encipherment. This example used the key word CORSICA, the message being the following words of Napoleon : "For the maintenance of peace, nations should avoid the pin-pricks which forerun cannon-shots."
In translating this into cipher, the key (a) was written, letter for letter, above the message (b). The substitute for each letter was then found in the alphabet indicated by its key letter. The first message letter, F, for example, is represented by T in the "C" alphabet; similarly, O becomes H in the "O" alphabet; and so on, as shown at (c). Grouping by fives (d) is for convenience in transmission.
(a) CORSICA CORSICA ... (b) FORTHEM AINTENA ... (c) THJKYSZ OPFKVMN ... (d) THJKY SZOPF KVMN ...
In using the Porta cipher it is convenient to encipher all letters falling under any given alphabet at one operation.
Cipher No. 190, by the way, offered the solver a neat little problem. The key length of seven letters was, of course, plainly shown by the repeated groups AGK and WZ at intervals of 42 and 7 letters, respectively. But the shortness of the cryptogram somewhat complicated matters.
Here, for example, the word FOR with the first three letters of the cipher would give the key CD-OP-OR, providing probable three-letter sequences throughout the cryptogram at intervals of seven letters. These are readily expanded until you have the complete translation.
For another Porta cipher turn to No. 193 in this issue.
Last week's No. 188, by M. Walker, was a hot crypt and no mistake. From total and final frequencies, however, Q and H stand out as substitutes for e and s, respectively. Then the suffixes -KVQ and -KVA are worth trying for -ine and -ing.
Substitute now in HKVXQ AIHHKWH and you have "sin-e g-ssi-s" —since gossips—and so on to the message in full: "Clandestine amatory escapades oftentimes eventuate disastrously since gossips, favoring conventionality, disseminate adverse innuendoes."
Mrs. M. B. Parran's "Berilla Code." No. 189, uses accompanying table, similar in principle to the condensed Porta table in last week's issue. The figure 6 at the beginning of the cryptogram indicated the number of columns in the table. A different alphabet is used for each line of the cipher.
In effect this system is a succession of simple substitution ciphers. Once this fact is determined, resolution quickly follows by methods applicable to such ciphers. Mrs. Parran's message : "This system is easy to decipher if the key is known, but I think that it will not be easy without it. We have used it quite a bit, and, so far, have found no one who could translate it."
1 2 3 4 5 6 A N Z Y X W B O N Z Y X C P O N Z Y D Q P O N Z E R Q P O N F S R Q P O G T S R Q P H U T S R Q I V U T S R J W V U T S K X W V U T L Y X W V U M Z Y X W V
On this week's bill, besides the Porta cipher, you will find an ingenious limerick crypt. No. 191, and a transposition cipher. No. 192, to tempt you.
CIPHER No. 191, by Mrs. Nona Fitzpatrick. St. Louis, Missouri.
Ifkaybode pxt x sbov nrbbo pfdeq Fk Jbufzl, ’qtxp x yriicfdeq. “Xjxvvfkd!” clihp zofba. “Mibxpb hbbm qeb yrii qfba.” Yrq lro ebol bkglvba fq xii ofdeq.
CIPHER No. 192, by L.Bekasi. New York City.
TSIES MSLSO NIRIQ BNETT OOEIE IDDOF ATPSR SSADE RNNIP FNIIL YCILF UFION YHTSM IPAEI UEREN GLOSA MBRMZ ENNOK APUAB EPIPE EACDL AADRS IDUFT OTSOL
CIPHER No. 193.
KGHGW TYVWF QQVGE CSVGD VZBOR NBBFJ RCEJV TSYBG MLUUQ GNCFV ATFVX UOKUY BLBCS V