US2293232A - Cryptographic device - Google Patents

Description

Aug. 18, 19.42. H.R. WELLER GRYPTOGRAPHIC DEVICE Filed July 22, 1941 Patented Aug. 18, 1942 cream CRYPTOGRAPHIC DEVllCE Harry R. Weller, Los Angeles, Calif.

Application July 22, 1941, Serial No. 493,525

5 Claims.

The invention reiates to a cryptographic device and has for an object to provide a cryptographic device which will meet the following requirernents; involve the use of letters, employ a cryptographic text no longer than plain text, simple to operate, require only one operator, simple in construction and light in weight, and errors not cumulative.

Concerning the item of secrecy, the object of the invention is to provide a device for treating the letters of a message, with a variable key, in fact aplurality of keys to govern the result of the basic steps, the specific key or keys being readily changeable, whereby it is practically impossible for the adversary to decipher the message, even with knowledge of the basic idea, unless certain specific keys are known.

Preferably the invention makes use of a plurality of keys, with means for compounding them in such a manner to thereby associate in paired relation the cryptogram letter and its corresponding message letter.

The device may be operated in accordance with a set-word and a pass-word which are extraneous groups of five letters each arbitrarily placed before, after or between the letters of the cryptogram, and are not a part of the cryptograrn proper as hereinafter treated.

The purpose of the letters in the set-word and password is merely to indicate to the recipient of a transmission the precise fixation of discs relative to each other necessary to decipher that particular cryptogram. The letters of the setword or pass-word if desired may also be used to indicate to the recipient of a cryptogram the exact location in some book where the keys are to begin.

The cryptogram proper is only that part of the transmission which when processed in conjunction with the keys will reveal the message. Hence neither the set-word nor the pass-word need to be processed with the keys, whereas the cryptogram does.

Suppose the set-word or pass-word is placed as the first five letters of the transmission. Then the keys must be placed so as to be operated in conjunction with the sixth and succeeding letters of the transmission. Only that part of the transmission which necessitates the use of the keys to translate it is referred to herein as being the cryptogram.

For further details of the invention, reference may be made to the drawing wherein Fig. l is a plan view of a cryptographic device according to the present invention.

Fig. 2 is a central sectional view of Fig. 1.

Fig. 3 is a sectional View on line 33 of Fig. 2 looking in the direction of the arrows.

Fig. 4 is a plan view with parts broken away of the device of Fig. 1 to which has been added a supplementary adjustable number disc.

Fig. 5 is a sectional view on line 55 of Fig. 4, the section including the parts broken away in Fig. 4,

Referring in detail to the drawing, the cryptographic device 6 comprises a rotatable disc 2 arranged between the relatively stationary discs I and 3. The discs I, 2 and 3 are mounted on a bolt 5 having a nut 6. Between the head i of the bolt 5 and the disc 3 is arranged a washer 8. Between discs 2 and 3 is washer 9. Disc 2 has a central circular aperture It in which fits the washer I i, so that disc 2 may rotate with respect to discs I and 3. Washer II is thicker than the disc 2 so as to prevent the latter from being clamped, when the nut 6 is screwed down tight, between washer 9 and washer I2 which is between disc I and washer Ii. Between disc I and the nut 6 is a washer iii. With the nut E5 screwed down tight, the discs I and 3 are clamped to the bolt 5, While disc 2 may rotate on the washer II.

The three discs I, 2 and 3 serve as alphabet carriers, the disc 3 having an array M of alphabet letters arranged in any desired order or scrambled and in a certain sequence, the disc as shown at 28 having said array of letters arranged in the same sequence as disc 3, while disc 2 has said sequence of letters arranged in the reverse order from discs I and 3 as shown at I9.

As shown in Fig. 3, disc 3, underneath the edge of disc 2 may have an array I5 of numbers, one of which is associated with each of the letters in the array I4.

If desired, the array I5 of numbers instead of being in fixed relation to the array It of letters on disc 3, may be changeable with respect thereto and for this purpose I arrange an array I6 of numbersas shown in Fig. 4 on a disc H which is mounted on bolt 5 between washer 9 and disc 3 as shown in Fig. 5, the nut Ii to be unscrewed slightly to permit disc I? to be rotated to a desired position where its tab It will be aligned with a desired one of the letters of array It for the purpose hereafter described.

Assume it is desired to encipher the following message:

There is only one absolutely, etc.

Preferably I use two keys to operate the device 5. Select two sentences at random to be used as the keys. Let us use the following extract from a book for the first key:

Houses, to such a one, in summer, etc.

For the second key let us use the following extract from the same book:

In any case, when men are, etc.

Write the two keys one below the other. It is immaterial which key is written first, because the array I9 of letters on disc .2 is arranged in reverse order to the array I4 on disc 3, and to the array 20 on disc I, with the result that, if we read the first letter H of the first key on disc 3 and align it with the first letter I of the second keyon disc 2 as shown in Fig. 1, these discs have the same position if we read the letter I of the second key on disc 3 and the letter H of the first key on disc 2. In other words, a given pair of letters, one of which is on disc 3 and the other is on disc 2 determines one relative position of these two discs, regardless of the order of which these two letters are read on these two discs. As the array I9 of letters on disc 2 is reversed to the array on disc I, the same thing applies here.

To proceed with enciphering a letter, write the desired message under the two keys. If the spaces between the words are omitted, the letters will fall in their proper places under each other, and the chances for errors to occur are reduced.

For the sake of clearness and definition, let us refer to the two keys and the message, when so prepared, as the ground. The ground then will appear as follows with the cryptogram added:

Keys --(HOUSESTOSU (INANYCASEW Message THER.EISONL Cryptograrn WSRMZ NYT Now take the cipher device 4. To operate the device 4 it must first be set. To set the device 4, choose some word or jumble of letters for the set-word. Let us choose the word Amber. Loosen the thumb-nut 6 and adjust the three discs so that when reading from the large discs 3 to the smallest disc I, the letters AMB will juxtapose or align as shown in Fig. 1. Tighten the nut 6 and the device 4 is ready to operate.

One general rule for both enciphering and deciphering with this device 4 is as follows:

When the two key letters are juxtaposed on the large disc 3 and rotatable disc 2, the message and cipher letters will juxtapose on the small disc I and rotatable disc 2.

Another general rule for both enciphering and deciphering with device 4 is as follows:

When two key letters are juxtaposed on the small disc I and rotatable disc 2, the message and cipher letters will juxtapose on the large disc 3 and rotatable disc 2.

Dealing with the general rule first given above, consider the first letter of each key. They are H and I. Turn the rotatable disc 2 until one of these letters on it juxtaposes with the other of these letters on the large disc 3, as shown in Fig. 1.

Now look around on the small disc I until you find the first letter of the message, which is T. Notice that this letter T on the small disc I juxtaposes or aligns with the letter W on the rotatable disc 2. This letter W is the first letter of the cryptogram. Write it down under the first letter of the message on the ground.

Now take the second letter of each key. They are 0 and N. Turn the rotatable disc 2 until these two letters juxtapose on the large disc 3 and rotatable disc 2. Then look around until you find the second letter of the message H on the small disc I. It will be found juxtaposing with the letter S on the rotatable disc 2. This letter S is the second letter of the crytogram.

The third letter of the keys are U and A. Juxtapose these letters on the large disc 3 and rotatable disc 2. Look around on the small disc I to the third letter of the message E. This juxtaposes with the letter R on rotatable disc 2 for the third letter of the cryptograrn.

Continue in this manner until the whole message is enciphered.

To decipher By prearrangement, the recipient of a cryptograrn must know, or be able to determine three variables, namely the set-word and both keys. Suggestions regarding this are given later.

When a cryptogram is received for decipherment, the recipient writes the two keys, one below the other as was done to enoipher the message. It is immaterial which key is written first, for reasons above noted. Then he writes the cryptogram under them instead of the message.

When this is done, the ground will look as follows with the message added:

Keys -(HOUSESTOSUC (INANY CASEWH Cryptogram WSRMZ NYTKEI Message -THEREISONLY He then takes the cipher device and sets discs I and 3 to the first and third letters of the set word, i. e. A and B as before. By proceeding exactly as was done to encipher the message, namely by reading the pair of lettersone from each key-on discs 3 and 2, the cryptogram and message pair, may be read from discs I and 2.

With the method just described, wherein the pair of letters, one from each key is read on large disc 3 and small disc 2, the message may be both enciphered and deciphered with the said result if the first key K1, the second key K2, the message M, and the cryptogram C, are read on discs I, 2 and 3 in any one of the four following orders:

KiKzM C WNNOO NNl- H HHNN HNN

[ Dl-I- mowing NMOOQ To transmit numbers When transmitting numbers in the body of a message, it is common practice to let the first few letters of the alphabet represent the numerals, thus: A for 1, B for 2, C for 3, D for 4, E for 5, F for 6, G for 7, H for 8, I or J for 9, and Z for 0. When this is done the letter X may immediately precede and follow the letters, so as to indicate to the recipient that these letters represent or stand for figures, thus: I saw 148 ducks should be written I saw XADHX ducks. Other conventions may be used.

The set-word and the two keys One use of the set-word has been described above. The following described use of the setword may be employed to introduce a fourth variable.

The set-Word, when used in conjunction with the figures n the large disc 3, may be used to indicate to the recipient the page, line and word of some book where the keys are to begin, and thereby identify the keys.

This is a great convenience because the recipient will not need to know in advance what keys have been used, but merely the book from which they are taken.

Suppose the book we choose, in which to locate the keys, contains 438 pages, approximately 45 lines to the page, and about words to the line. Suppose we choose for the set-word the letters NCLJQ which are sent to the receiving station.

The recipient should proceed as follows: Loosen the thumb-nut 6 of the device 4 and adjust the three discs I, 2 and 3 so that when reading from the large disc 3 to the small disc the letters NCL will juxtapose or come together as shown in Fig. 1. Tighten the nut 6, being careful to hold the rotatable disc 2 from turning.

Now lifting up the edge of the rotatable disc 2, he sees the figures 1, 18, 10, 24, and 3 on the large disc 3 behind or back of the respective letters of the set-word on the rotatable disc 2. figures in a row as follows: 11810243.

Start at the left and use as many of these figures as possible for the page number. We therefore look on page 118 for the key.

Now use as many more figures as possible for the line. Therefore we look in line 10.

vNow using as many more figures as possible will give us the word in the line. This gives us word 2.

All of which means that the first key will begin with the second word of the tenth line on page 118 of whatever book we have selected.

For the second key we can use this same row of figures, but reverse their order. We then have the figures 34201811.

Now using the same procedure as before, We start at the left and use as many figures as possible for the page number. This gives us page 342.

Then using as many more figures as possible for the line, we get line 18.

Then using as many more figures as possible to locate the word in the line, we get word 1.

Therefore we find our second key starting with the first word in the 18th line on page 342.

The sender after enciphering his message with these two keys, incorporates that jumble of five letters (the set-word) as the first group of letters in the cryptogram.

When the recipient receives the cryptogram, he knows by prearrangement, that the first five letters of it are the set-word and proceeds to set discs l, 2 and 3 of his device 4 to it as described above. He then converts this set-word into figures as just described, so as to locate the two keys, and can then decipher the message if he has an Write these exact copy of the same book and a similar device 4.

Changing keys In nearly all cases where cryptograms are used, the keys are changed every so often as a precaution against any undesired person learning how to read the cryptograms. This is many times more necessary in military work.

By using a different set-word each time a new message is enciphered, the keys can be changed for each new message.

This is a great safety factor because it prevents the enemy from comparing captured cryptograms, and if possible, deciphering them.

The pass-word In important communications where it is desired to prevent the enemy from learning the setword and its secrets, the head office chooses a new set-word every so often, and transmits it to those who send and receive cryptograms.

These set-words should not be decided upon far in advance of their need, and no standing rule or formula should be employed to determine them. They preferably should be chosen by chance and transmitted separately from any cryptogram.

Then in order to change the keys for every cryptogram, as mentioned above, a meaningless jumble of any five letters (called the pass-word) could be incorporated as the first word of each new cryptogram. To illustrate, let us choose the letters EMKSY for the pass word.

It is made use of as follows: The cryptographer first converts the set-word into numbers as described above by selecting the proper numbers from array E5 on disc 3, and then still keeping the discs I, 2 and 3 of device 4 set to the setword and holding the rotatable disc 2 so it cannot turn, he proceeds to convert the pass-word into numbers in the same Way. He then adds these two sets of figures together as follows:

Set word :NCLJQ =1l8l0243 Pass-word=EMKSY=23158169 Added together =34968412 He then determines the page, line and word for the two keys from this total as previously described for the set-word.

If the enemy is familiar with the cipher machine 4 and its basic method of operation, this combined use of the set-word and the pass-word will effectively prevent him from deciphering the message. Assuming the enemy has the cryptogram, he must capture the set-word before he can learn even one of the keys.

Baffle disc The bafile-disc is a safety device which introduces another variable. Its use is optional.

No cipher system or device is proof against traitors or spies, but this double-key cipher device can be made nearly so by the use of a temporary auxiliary disc ll called a bafile-disc, shown in Figs. 4 and 5. This disc I! does not make the cryptogram any more difiicult to break, but it does effectively forestall treachery and espionage.

The disc I! is out the same size as the rotatable disc 2. A projection It extends from one side of it to facilitate turning the disc I! when the device 4 is assembled. The disc 11 contains the numbers from 1 to 26 inclusive scrambled around its edges as shown at [6 in any arrangement the crytographers may desire, but they preferably should be scrambled by chance.

When the baffle-disc H is used, it is assembled upon the bolt 5 between the large disc 3 and the washer 9.

To use the disc II, it must first be set. To set the disc ll, choose any letter of the set-word such as the last letter. Turn the disc I! till the projection or tab E8 on it juxtaposes with this letter on the large disc 3. Then the numbers on it instead of those on the large disc 3 are used to convert the letters of the set-word and the password into numbers from which the keys are determined.

New baffle-discs with entirely different arrangements of the numbers should be made every so often. These new baffle-discs can be lettered serially to distinguish one bafile-disc from another. Also some other letter such as the fourth letter of the set-word .could be used to indicate to the correspondent which baffle-disc had been used.

By pre-arrangement with the correspondent, any other method may be used if preferred, for setting the discs or for indicating which disc had been used.

These baffle-discs, when used in conjunction with the set word and the pass-word, will completely baffle anyone familiar with the operation of the machine and the secrets of the set-word, pass-word, etc.

As a modification, I may dispense with one of the fixed discs, for example the small disc I and by juxtaposing the corresponding letters of the two keys on discs 3 and 2, for example assuming the keys above chosen, the letter H on disc 3 is aligned with letter I on disc 2 as shown in Fig. 1, and then by reading the message letter T on disc 2 we find in paired relation therewith the cryptogram letter V on disc 3. As a further modification, I may use only one fixed disc and one rotatable disc and arrange the alphabet letters thereon in the same sequence instead of the reverse sequence just described. In both cases, the message can be deciphered by reading the crytogram letter on the same disc on which it was read for enciphering, although in the first modification, both discs, keys, cipher and message letter, are interchangeable at any time while enciphering or deciphering a message, although in the latter modification none of them are interchangeable at any time.

It will be apparent that various other modifications may be made in the invention without dea parting from the spirit of the following claims.

I claim:

1. A cryptographic device comprising a pair of alphabet carriers having the letters of the alphabet thereon in the same sequence, a relatively movable alphabet carrier therebetween and having said sequence of letters in the reverse order, and common means holding said pair of carriers in selective fixed position and movably supporting said relatively movable carrier.

2. A cryptographic device according to claiml comprising an adjustable number carrier associated with one of said pair of carriers and having a number for each letter thereon. 5

3. A code device comprising three superposed discs graduated in size with alphabets arranged in the same irregular order on the peripheries of the largest and smallest ones of said discs and with an alphabet arranged in the reverse of said irregular order on the intermediate one of said discs, a washer between said largest and smallest discs, said intermediate disc being thinner than said washer and rotatably mounted thereon, a bolt centrally located of all of said discs and said washer and having a nut for clamping said largest and smallest discs in selective fixed relation while permitting rotation of said intermediate disc relatively thereto.

4. A code device according to claim 3 comprising a number disc substantially the same size as said intermediate disc and having a number for each letter on said intermediate disc, said bolt and nut comprising means for clamping said number disc in selective fixed relation relatively to said largest and smallest discs, and a tab on said number disc for shifting the same manually to different positions.

5. A code device comprising three superposed discs graduated in size with characters arranged on the peripheries thereof, a washer between the largest and smallest of said discs, said intermediate disc being thinner than said washer and rotatably mounted thereon, a bolt centrally located of all of said discs and said washer and having a nut for clamping said largest and smallest discs in selective fixed relation while permitting rotation of said intermediate disc relatively thereto.

HARRY R. WELLER.

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