The Jefferson disk, also called the Bazeries Cylinder or wheel cypher as named by

Thomas Jefferson Thomas Jefferson (April 13, 1743 – July 4, 1826) was an American statesman, diplomat, lawyer, architect, philosopher, and Founding Father who served as the third president of the United States from 1801 to 1809. He was previously the natio ...

, is a

cipher system Cipher System is a Swedish melodic death metal band from Tjörn. The band formed under the name Eternal Grief in 1995. They changed their name in 2001 to Cipher System. The band released their first album ''Central Tunnel Eight'' by Lifeforce ...

using a set of wheels or disks, each with the 26 letters of the alphabet arranged around their edge. The order of the letters is different for each disk and is usually ordered randomly. Each disk is marked with a unique number and a hole in the center of the disks allows them to be stacked on an axle. The disks are removable and can be mounted on the axle in any order desired. The order of the disks is the cipher key, and both sender and receiver must arrange the disks in the same predefined order. Jefferson's device had 36 disks.Kahn, p. 194 Once the disks have been placed on the axle in the agreed order, the sender rotates each disk up and down until a desired message is spelled out in one row. Then, the sender can copy down any row of text on the disks other than the one that contains the plaintext message. The recipient has to arrange the disks in the agreed-upon order, rotate the disks so they spell out the encrypted message on one row, and then look around the rows until they see the plaintext message, i.e. the row that's not unreadable. There is an extremely small chance that there will be two readable messages, but this can be easily avoided by checking. The Jefferson disk was invented by

in 1795, and the same method was independently invented and improved upon by Commandant Etienne Bazeries, but did not become well known until he broke the

Great Cipher The Great Cipher (French: ''Grand chiffre'') was a nomenclator cipher developed by the Rossignols, several generations of whom served the French monarchs as cryptographers. The Great Cipher was so named because of its excellence and because it wa ...

, of

Rossignols The Rossignols, a family of French cryptographers and cryptanalysts, included Antoine Rossignol (1600–1682), Bonaventure Rossignol and Antoine-Bonaventure Rossignol. The family name means "nightingale" in French. As early as 1406, the word ' ...

, a century after Jefferson's work. The system was used by the

United States Army The United States Army (USA) is the land warfare, land military branch, service branch of the United States Armed Forces. It is one of the eight Uniformed services of the United States, U.S. uniformed services, and is designated as the Army o ...

from 1923 until 1942 as the

M-94 The M-94 was a piece of cryptographic equipment used by the United States Army, consisting of several lettered discs arranged as a cylinder. It was also employed by the US Navy, under the name CSP 488. The device was conceived by Colonel Parke ...

. It aided the war efforts as it was a type of secret messaging that only military and government officials would know how to interpret.

Example of Operation

To encrypt a message, the encrypter rotates the disks to produce the

plaintext In cryptography, plaintext usually means unencrypted information pending input into cryptographic algorithms, usually encryption algorithms. This usually refers to data that is transmitted or stored unencrypted. Overview With the advent of com ...

message along one "row" of the stack of disks, and then selects another row as the

ciphertext In cryptography, ciphertext or cyphertext is the result of encryption performed on plaintext using an algorithm, called a cipher. Ciphertext is also known as encrypted or encoded information because it contains a form of the original plaintext ...

. To decrypt the message, the decrypter rotates the disks on his cylinder to produce the ciphertext along a row. Decryption is easier if both the encrypter and the decrypter know the offset of the row, but not necessary since the decrypter can look around the cylinder to find a row that makes sense. For example, a simplified "toy" Bazeries cylinder using only ten disks might be organized as shown below, with each disk "unwrapped" into a line and each marked with a designating number: If the "key", the sequence of disks, for this Bazeries cylinder is 7,9,5,10,1,6,3,8,2,4
and the encrypter wants to send the message "" to the decrypter, the encrypter rearranges the disks as per the key and rotates each disk to obtain the

, which is shown at the left, with spacing added for clarity: the encrypter then selects the ciphertext from the sixth row of the cylinder up from the plaintext. This ciphertext is also highlighted above with spacing, and gives:
When the decrypter gets the ciphertext, they rearrange the disks on their cylinder to the key arrangement, rotate the disks to give the ciphertext, and then read the plaintext six rows down from the ciphertext, or look over the cylinder for a row that makes sense.

Basis for later military ciphers

The Bazeries cylinder was the basis for the US "

" cipher machine, which was introduced in 1922 and derived from work by Parker Hitt. In 1914, Hitt had experimented with the Bazeries device, building one prototype using slides on a wooden frame, with the cipher alphabets printed twice consecutively on the slides, and then another using disks of wood. He forwarded his experiments up the Signal Corps chain of command, and in 1917

Joseph Mauborgne Joseph Oswald Mauborgne (February 26, 1881 – June 7, 1971) co-invented the one-time pad with Gilbert Vernam of Bell Labs. In 1914 he published the first recorded solution of the Playfair cipher. Mauborgne became a Major General in the U ...

refined the scheme, with the final result being the M-94. The M-94 used 25 aluminium disks on a spindle. It was used by the

Army An army (from Old French ''armee'', itself derived from the Latin verb ''armāre'', meaning "to arm", and related to the Latin noun ''arma'', meaning "arms" or "weapons"), ground force or land force is a fighting force that fights primarily on ...

Coast Guard A coast guard or coastguard is a maritime security organization of a particular country. The term embraces wide range of responsibilities in different countries, from being a heavily armed military force with customs and security duties to ...

, and the Radio Intelligence Division of the

Federal Communications Commission The Federal Communications Commission (FCC) is an independent agency of the United States federal government that regulates communications by radio, television, wire, satellite, and cable across the United States. The FCC maintains jurisdicti ...

until early in

World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposing ...

. The Army changed back to Hitt's original slide scheme with the " M-138-A" cipher machine, which was introduced in the 1930s and was used by the

US Navy The United States Navy (USN) is the maritime service branch of the United States Armed Forces and one of the eight uniformed services of the United States. It is the largest and most powerful navy in the world, with the estimated tonnage ...

and

US State Department The United States Department of State (DOS), or State Department, is an executive department of the U.S. federal government responsible for the country's foreign policy and relations. Equivalent to the ministry of foreign affairs of other nati ...

through World War II. The M-138-A featured 100 strips, with 30 selected for use in any one cipher session. It was an improvement in security for the State Department, which during the interwar years had used insecure codes, even in one case a standard commercial

telegraph Telegraphy is the long-distance transmission of messages where the sender uses symbolic codes, known to the recipient, rather than a physical exchange of an object bearing the message. Thus flag semaphore is a method of telegraphy, whereas p ...

code.

Cryptanalysis

The Bazeries cylinder was a relatively strong system at the time (compared to many other systems in use), and Etienne Bazeries, a French military cryptanalyst, is said to have regarded it as indecipherable. The "

Pers Z S The Pers Z S was the signals intelligence agency of the German Foreign Office (german: Auswärtiges Amt) before and during World War II. It consisted of two cryptologic sections. Pers Z S was the cryptanalytic section which was called ''Special Ser ...

" code-breaking group of the German Foreign Office cracked the M-138-A in 1944. However, by that time the Americans had more sophisticated cipher systems in operation. The French cryptographer Gaetan de Viaris (aka Marquis Gaetan Henri Leon Viarizio di Lesegno) who is famous for one of the first printing cipher devices (1874), solved the Bazeries cylinder in 1893. One major weakness of the Bazeries cylinder is that the offset from the plaintext letter to the ciphertext letter for the cipher alphabet on each disk will be exactly the same. In the example shown above, this offset is six letters. For example, if a

cryptanalyst Cryptanalysis (from the Greek ''kryptós'', "hidden", and ''analýein'', "to analyze") refers to the process of analyzing information systems in order to understand hidden aspects of the systems. Cryptanalysis is used to breach cryptographic sec ...

has captured the ten disk Bazeries cylinder described in the example above, this should not be enough to permit them to decipher messages with it, since they also have to know the key, or the arrangement of the disks on the cylinder. The number of possible permutations of the disks of the example Bazeries cylinder is:
Due to the large size of this number,

trial and error Trial and error is a fundamental method of problem-solving characterized by repeated, varied attempts which are continued until success, or until the practicer stops trying. According to W.H. Thorpe, the term was devised by C. Lloyd Morgan (18 ...

testing of the arrangement of the disks difficult to perform by hand.

Sources

* ''The Codebreakers,'' David Kahn, 1967, pp. 192–195 * "Monticello." Wheel Cipher. Accessed April 8, 2022. https://www.monticello.org/site/research-and-collections/wheel-cipher. * Riverbank Publication Number 20, ''Several Machine Ciphers and Methods for their Solution,''

William F. Friedman William Frederick Friedman (September 24, 1891 – November 12, 1969) was a US Army cryptographer who ran the research division of the Army's Signal Intelligence Service (SIS) in the 1930s, and parts of its follow-on services into the 1950s. ...

, 1918, i
Methods for the Solution of Ciphers, Publications 15-22
Rufus A. Long Digital Library of Cryptography, George C. Marshall Library, 1917-1922, * "Rossignols." Wikipedia. Wikimedia Foundation, November 19, 2021. https://en.wikipedia.org/wiki/Rossignols.

External links

Thomas Jefferson's Wheel Cipher
{{Cryptography navbox , machines, state=expanded American inventions Encryption devices Thomas Jefferson