Jefferson's cylinder is an encoder invented by Thomas Jefferson , consisting of 36 disks, each of which has an alphabet of 26 letters (not in order), the disks are worn on one axis and can rotate around it.
Content
Creation History
Jefferson's Cylinder is one of the first modern encryptors created by Jefferson between 1790 and 1800. Jefferson called his encryption system “disk cipher”. He himself was not sure of the reliability of his invention, so he treated him with caution and, as the president of the United States, did not use it, but continued to use traditional codes and ciphers. He maintained contact with the mathematician R. Pattersen , so that he would analyze this invention [1] . Since Jefferson did not impose his invention on use, pretty soon it was archived. In the 20th century, when the invention was found and remembered again, it was recognized as a cryptanalysis-resistant encryption device, and Jefferson himself was called the "father of the American encryption business."
Principle of Operation
The design of the encoder is as follows: a wooden cylinder is worn on an axis and cut into 36 disks, the English alphabet is applied to each of these disks in random order, the disks can rotate independently of each other. A line is highlighted above the cylinder surface, under which plaintext will be collected. The text to be encrypted is divided into blocks of 36 characters. The first letter of the block is on the first disk and is fixed under the highlighted line, the second is on the next disk, etc. Encrypted text is read from any other line except the plaintext line. Decryption is carried out on the same encoder: the ciphertext is composed under the selected line, plaintext is searched among parallel lines by finding a meaningful message. It is theoretically possible to find a meaningful text in several lines, but in practice, such a text was in only one line; and even if meaningful text could be found in several lines, then in the next step (in the next block of 36 letters), the line by which you want to read plain text is uniquely determined. The key is the order of letters on each of the disks and the order of the disks on the axis [1] . The number of keys is very large: . Even assuming that the cylinder itself could fall into the hands of an attacker, the number of keys remains very large: The order of the cylinders periodically changed: one order could be used for one or more messages, or not change during the day.
Cipher Example
In the book Secret History: The Story of Cryptology (2013), Craig P. Bauer, this code is given:
This cipher was created in 1915 by a cryptographer of the US Army, and, at the moment, it has not yet been decrypted. Bauer hypothesized that this cipher was created using the Jefferson encoder, so they could not decrypt it. [2] .
Analogs
Since the Jefferson encoder was archived, the invention was repeated by other cryptographers.
Bazery Cylinder
At the end of the XIX century, the invention was repeated by Etienne Bazery . Its cylinder consisted of 20 discs, each of which had 25 characters of the English alphabet. They refused to use his invention, calling it too complicated both in application and in manufacturing. Bazeri simplified his invention by declaring the order of letters not secret, and for ease of remembering, this order was easily formed from slogan phrases. This simplification greatly weakened the cipher; it became not reliable, as the Marquis de Viari showed by opening it. Cipher Bazeri was never adopted [1] .
Hitt Encoder
At the beginning of the 20th century, the idea was repeated by Parker Hitt with reference to Bazeri, stripes were used instead of cylinders here [1] .
M-94
In the 20s of the XX century, the idea was repeated in the United States again, recognized as resistant, adopted, and created the M-94 machine. The machine consisted of 25 thin disks with the alphabet rotating on an axis 110 mm long. It was used in the American army from 1922 to 1943. [3]
Vavi Instrument
In 1916, the invention was repeated in Russia. Manufactured by his second lieutenant Popazov, later it was called the "Vavi Device". The structure of the device was similar to that of the Jefferson cylinder, but instead of the disks, 20 rings were used, worn close to each other on the cylinder. A mixed alphabet of 30 letters was applied to 18 rings, and numbers from 1 to 30 were applied to the first and last rings. The key for this device was a set: a number, a letter, and a "step key" (two letters). For encryption, the message was divided into blocks of 17 characters, each block was encrypted separately. First, a number was determined, determined by the key, a letter was also set in front of it, also a key, and an open message block was lined up in front of them. Then the message was encrypted: two letters of the "step key" were found under the key letter, then the odd characters were replaced by the characters from the string corresponding to the first letter of the "step key", the even characters were replaced by the second, i.e. characters were taken alternately from different lines. This encoder had one significant difference from the Jefferson cylinder — the ciphertext was selected uniquely. The invention was not widely used [1] .
Attack de Viari
In 1893, De Viari carried out a successful attack on the Bazeri cylinder. The attack is based on the assumption that the attacker can use an encryption device, that is, the order of letters on each disk is known. Also, an attack will require a likely word (that is, a word that is likely to occur in clear text), this word should not be too long so as not to be interrupted by a periodic change of encryption lines. De Viari demonstrated his attack for the Bazeri cylinder and Giverger ciphertext (it is known that the message has a military theme):
Let the likely word be "division". Many cryptocurrency characters are read vertically under clear text characters. Since the location of the letters on the disks is known, it is accordingly known which letter the plaintext letter will replace when shifting by a certain number of characters on the disk. The figure shows all the possible encryption of each character in plaintext, with a shift of 1 character (left), with a shift of 4 characters (right).
For each position of the likely word, you can determine whether all the corresponding characters will be among the available ones. That is, for the word “division”, 8 consecutive letters of the ciphertext should meet (with a fixed shift) at the desired positions (that is, in the correct sequence). This way all possible shifts are checked up to the first match. In an attack conducted by de Viari, such a match was found at a shift of four and with a combination of HLOERTXV. That is, the order of the disks has already been partially determined (based on the previous figure).
Thus, knowing this order, it is possible to decipher words or their fragments in other lines of the ciphertext at the same positions. For example, the word “departas” is deciphered in the third line.
For each line there can be different offsets (for the third line, the offset is 22). Knowing French, the word “departas” can be continued in two ways “departasixheures” and “departaseptheures”. We assume that 6 hours is quite early and begin further decryption using the word “departaseptheures”. We experience his piece of "ptheures" in the fourth line.
This determines the position of another five disks unambiguously and three disks ambiguously (in two versions).
Subsequent decryption takes place according to the same scheme for selecting the logical end of a word. Thus, the position of all disks becomes known and the message is easily decrypted.
The end of the message is filled with dummies. An attack works even in the absence of a probable word, using, for example, the standard endings “ation” for English and French [4] .
Notes
- ↑ 1 2 3 4 5 A.V. Babash, Doctor of Physics and Mathematics, Professor, Yu. I. Goliev, D.A. Larin, Ph.D. N., G.P. Shankin, d.t. Professor, Cryptographic Ideas of the 19th Century - Confident Magazine
- ↑ Craig P. Bauer Secret History: The Story of Cryptology
- ↑ F. Bauer Methods and Principles of Cryptology - World, 2006 - p.147-149
- ↑ F. Bauer Methods and Principles of Cryptology - World, 2006 - p.306-311
See also
- Violet M-125
- Enigma
- M-209
Literature
- F. Bauer. Methods and principles of cryptology. - World, 2006 .-- 568 p.
- Craig P. Bauer. Secret History: The Story of Cryptology. - Chapman and Hall / CRC, 2013 .-- 620 p.
- David Kahn. The Codebreakers: The Comprehensive History of Secret Communication from Ancient Times to the Internet. - Scribner, 1996 .-- 1200 p.
- A.V. Babash, Yu. I. Goltsev, D.A. Larin, G.P. Shankin. Cryptographic ideas of the XIX century // Confident: journal. - 2004. - No. 1 . - S. 88-95 . Archived December 8, 2014.