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Jefferson Wheel Cypher

(Download this presentation M-94 Cylinder Cipher: A Story of Innovation, Intrigue, and Deception or view it online)

Jefferson Cypher Wheel found near Monticello
Thomas Jefferson in 1791

Thomas Jefferson (yes, our third president) invented his "wheel cypher" in the 1790s, and what a deceptively innovative little device it is! In fact, it was so far ahead of its time, this type of cipher was still in active use in the US military 150 years later at the beginning of WW2. Only one original Jefferson cipher wheel is known to exist, which is in the NSA cipher museum in Ft. Meade, Maryland.

The Jefferson cipher had 36 wheels arranged around an axle with a different random alphabet printed on the outside of each wheel. This is a polyalphabetic cipher and at first pass it may seem to be similar in function to a Vigenère disk with a 36 character keyword, but it is not. Each of the wheels has a different substitution alphabet, unlike using the same Vigenère wheel 36 times. Also, the wheels are arranged simultaneously instead of serially, so this type of device is usually called a multiplex cipher. You could keep up a secure correspondence with many others by having a different wheel arrangement or completely different wheels with each person.

The key is not a repeating keyword but the order of the 36 wheels on the axle, each wheel having a different cipher. There are 36 X 35 X 34 X...X 2 X 1 (= 36! or 36 factorial) ways to arrange 36 wheels on an axle, which is 3.72 X 1041. Jefferson calculated this number exactly, calling it "372 with 39 cyphers [zeroes] added to it." This compares favorably to the 3-rotor Enigma machine, which has a key space of 1023. So a brute force attack of the Jefferson wheel cipher would be more difficult than the Enigma, but the Enigma machine is much more difficult to break in practice. In fact, the Germans broke the US M-94 because of the repeating wheel order for each message greater than 25 characters and the standardized headers in some military messages.

Read Thomas Jefferson's description of his wheel cypher.

The fact that Jefferson invented this device was only discovered by a researcher looking through his papers in the Library of Congress in 1922. This was independently and coincidentally invented that same year by Joseph O. Mauborgne of the US Army. It was called the M-94 Cipher Device and was in use until 1943. At least, this has been the accepted story of the invention of the M-94 for many years, but this re-invention story has recently changed!

To use the Jefferson cipher wheel, the sender of a cipher message would arrange her disks in the agreed upon order and then simply spin each disk to spell out the first 36 letters of the message. There were no numbers, punctuation or spaces. Any other of the 25 lines can be sent as the encrypted message. The receiver of the message would arrange his cipher wheels in the prescribed order and then spell out the enciphered message across one horizontal line. By scanning across the other 25 lines of gibberish, the plain text message will stand out.

Chinese combination lock

This procedure would have to be repeated for the next 36 letters of the message, and so on. Jefferson's cipher wheel was beyond a doubt the most advanced, secure and user friendly cipher system of its time. He seems to have invented it out of the clear blue, as his existing papers and letters do not show a study of the science of cryptology. He may have gotten his inspiration for this cipher device by reading about or seeing the Chinese combination lock like the one pictured above. It is known that Jefferson subscribed to a magazine which had an article describing this lock, which was popular in France while he was there in the early 1790s. Jefferson was also familiar with a variety of ciphers devices and expressed an interest in ciphers to exchange messages with his school friends. As the first Secretary of State for the new United States of America, he used a cipher system called nomenclator, which later developed into code books. Nomenclator is a combination of cipher and codes. As President, he selected the Vigenère cipher as the official cipher for the Lewis and Clark expedition.

Dr. Robert Patterson, a mathematics professor and President of the Philosophical Society, sent Jefferson a letter in 1802 recommending a cipher system which is called columnar transposition, with nulls at the beginnings of the columns. Jefferson responded back to Dr. Patterson, "I have thoroughly considered your cypher, and find it so much more convenient in practice than my wheel cypher, that I am proposing it to the Secretary of state for use in his office." Later, he followed up in another letter, "We are introducing your cypher into our foreign correspondences."

That Jefferson did not recognize his wheel cypher to be far superior to Patterson's cipher does not speak too highly of his cryptologic understanding. If he would have recommended his own cipher, the US would have benefited from a much more secure system well into the 20th century. Instead, his cipher was buried in obscurity until it was rediscovered among his papers in 1922.

Jefferson Wheel Cypher from National Cryptologic Museum in Ft. Meade, MD

The cipher wheel shown here was found in a home near Jefferson’s Monticello home and is an exact match to Jefferson's description of his "wheel cypher.” The 36 wheels are made of wood and it has been dated to the late 1700s. It is a French language cipher device with 40 characters around the circumference rather than 26. The extra 14 characters may be the 14 French letters that have accent marks but the letters are too faint to tell from the photographs. The left side of this device has a bracket with a hole in it which is used to insert a brass rod. The rod would then go through all 36 disks and into the right side of the frame, keeping the letters lined up and fixed for encoding or decoding a message.

Jefferson's cipher wheel was reinvented at least twice. Étienne Bazeries, a French military cryptanalyst, invented his Bazeries cylinder in 1891, but it was never adopted by the military. Then Captain Parker Hitt of the US Army independently invented it in strip form in 1912. Joseph O. Mauborgne redesigned the strip cipher into the cylinder cipher in about 1917. The cylinder cipher was named the M-94 and has been historically credited to Mauborgne for almost 100 years, until 2015.

M-138A Cipher Device from the
National Cryptologic Museum in Ft. Meade, MD

In 2015, Betsy Rohaly Smoot, an NSA historian, reported that the original invention of the M-94 should be credited to Parker Hitt in 1912. It turns out that he invented both the strip form and the cylinder form of this cipher device. He even had wood prototypes made with the help of his cryptanalysis class in 1912. His first device was made of wood and had 12 pairs of wheels. Each pair had the alphabet in normal sequence on one wheel and in reverse sequence on the other wheel. He designed this device as a convenient way to decrypt enemy messages and also to use as a cipher device. He recommended the use of 25 or 30 wheels and said they could be of mixed alphabets. He even suggested making the device out of stamped metal.

Hitt did not pursue this cylinder design in favor of a strip version, which he considered more suitable for battlefield conditions. This strip cipher was developed into the M-138. A prototype of the strip version was made of wood in 1912 and was finally deployed in 1934 in aluminum with 25 channels for strips of mixed alphabets. The advantage of this device over the cylinder was the ability to have many strips of different alphabets available, instead of the 25 fixed wheels in the M-94. The M-138 was replaced in 1938 by the M-138A, which had 30 channels of alphabet strips. This cipher device was in use until the 1960s.

Mauborgne used the Hitt design and came up with a stronger mixed up alphabet and had the Signal Corps manufacture it. He had 2 prototypes made of solid brass on a base of wood. The all-aluminum M-94 was first deployed in 1922 and was in use until August of 1943. By then, enough replacement M-209 ciphers were available to make the M-94 obsolete. A total of 9,432 M-94s were manufactured, compared to about 140,000 M-209s.

Parker Hitt (1878-1971)

In 2016, a different and previously unknown version of the M-94 came to light, but it was probably never officially deployed. It is made of brass on the ends but uses Bakelite for the wheels. It seems to be a transition between the original prototype and the aluminum M-94. Pictures of this device are displayed below as device 6.1.

Mauborgne would go on to cryptologic fame with several breakthroughs to his credit. The first was a solution to the Playfair cipher, used by the British as their field cipher. It was the first digraphic cipher, meaning that the cipher was based on pairs of letters in plaintext being enciphered into another pair. Two pairs of plaintext letters with a letter in common could produce ciphered text with no letter in common. So this is a polyalphabetic cipher that would be immune to letter frequency analysis. The Playfair cipher was invented by Charles Wheatstone who named it after his friend Lyon Playfair, who advocated its use for the British military (see Chapter 7). Mauborgne had the first recorded solution to the Playfair cipher in 1914, authoring the first work on cryptology published by the US government.

Mauborgne was also credited with the invention of the first theoretically unbreakable cipher in 1919, called the one-time pad, along with co-inventor Gilbert S. Vernam. Unfortunately, this story will also be superseded by a later discovery, as the side story of cipher inventions being misattributed goes on.

Joseph O. Mauborgne (1881-1971)

In 1914, Mauborgne was one of the first to demonstrate the use of two-way radio communications between an aircraft and a ground station. This innovation changed air warfare from individual airplanes into a coordinated air force. Both the airplane and the radio were new inventions which would go on to have enormous impact on the history of military strategy and success. Later, as a two-star general and Chief Signal Officer, Mauborgne built and directed the team, led by William F. Friedman, which solved the Japanese Purple cipher in 1940. He retired a few months before Pearl Harbor.

Mauborgne was also an accomplished artist, his portraits and etchings are displayed in several prominent galleries as well as private collections. He was also interested in music and violin making, for which he won an international competition in The Hague in 1949.

The US M-94, except for the number of wheels, is an exact replica of Jefferson's cipher wheel. Jefferson's invention of this 125 years earlier, while being somewhat preoccupied with the founding of a new country, is testament to his extraordinary genius. The concept of a rotor device with interchangeable wheels was the precursor to the various electrical, rotor-based cipher machines, such as the Enigma machine, which were developed at the close of WW1.

More Information on Code Wheels

Identify Friend or Foe Code Wheels

Jefferson Wheel Cipher

from the Cipher History Museum

Lugagne Strip Cipher - 1912


The Lugagne strip cipher is a strip form of the Jefferson cipher wheel invented by Georges Lugagne in 1912 in France. It has 20 strips of mixed alphabets, in which 10 strips can be placed at the top of the cipher and paired with another 10 strips at the bottom of the device. The plaintext is aligned along the upper rule line and the ciphertext will appear along the lower rule line. Since these rule lines are fixed, this is not a multiplex cipher like the Jefferson or M-94 cipher devices, but the moveable strips function as the wheels in those devices. Since the strips are paired, the keyspace is 10! X 10!, or 1.3 X 10**13. This is a respectable cipher device for its time, but much less secure than the M-94 or the Bazeries Cylinder, so it was not used for military purposes.

This Lugagne cipher was made by Barbotheu, a famous French slide rule maker, which is evident in the construction. It is made of mahogany and ivory, with nicely engraved letters and ball-bearings under the strips.

US Army M-94 Cipher Wheel Prototype – 1917-1921


Parker Hitt independently re-invented the Jefferson cipher wheel in 1912. He also invented the strip cipher, which he thought was better suited for battlefield conditions, so he pursued that design. The strip cipher became the M-138 and the cylinder cipher was developed into the M-94. Hitt’s original cylinder device used wheels with the alphabet in normal or reverse sequence, Joseph O. Mauborgne strengthened the cipher by making the wheels with a random alphabet order and unique for each wheel. While several M-94 prototypes were made, the brass and Bakelite version above is the only one of this type known to exist.

US Army M-94 Cipher Wheel - 1922-43


The cipher wheel was originally invented by Thomas Jefferson around 1795. His invention was lost to history until discovered in his writings in 1922. Coincidentally, this was the year it was released by the US Army and named the M-94.

The M-94 has 25 disks, with a different alphabetic arrangement around each wheel. The wheels are stamped B-Z and 1-25 on the inside surface and the key is the order of the wheels on the axle. A message is spelled out on the arm, and any of the other 25 lines of text is sent as the cipher. The brass M-94 above is a prototype device, the aluminum version is the one issued to the military. 9,432 were manufactured and it remained the primary battlefield cipher for the US until it was replaced by the M-209 in 1943.

Da Vinci Code Wheel - 2006


The Da Vinci code wheel was used in the movie, “The Da Vinci Code,” which premiered in 2006 and was based on the book of the same name by Dan Brown.

This code wheel was made by Cryptex and when the wheels are lined up to the correct keyword, the ends separate revealing a secret vault inside. In the book, this vault held a papyrus scroll wrapped around a vial of vinegar. If someone tries to force open the vault, the vial would break and make the papyrus illegible.

US IFF Code Wheels with ABA-1 Radio Set - 1940s


Because of the advancement of radar and faster airplanes in WW2, the need to “identify, friend or foe” became necessary for the pilots. IFF gave the pilot warning before an enemy plane was visible.

IFF radios needed security to prevent the enemy from spoofing the signal or using the IFF radio from a downed plane. Each pilot was issued this small metal box of 10 code wheels, one of which was inserted in the dynamotor of the ABA-1 radio. The cogs of the code wheel engage a Morse code type device, sending the expected response to other friendly aircraft. These radios have no dials or adjustments, they are entirely automated. A red self-destruct button was used to prevent enemy capture of this important radio by detonating a charge inside the radio.

US KY-65 Emergency Aircraft Keyer - 1940s


The KY-65 is a radio controlled device which will automatically transmit the aircraft tail number on a regular basis in the event of an emergency.

A plastic wheel is provided with tabs around the circumference. Some of the tabs are removed to create Morse code for the last 4 digits of the aircraft tail number. The signal can be set to start transmission after 5 to 30 seconds of an emergency.

Lithographs by Chief Signal Officer Joseph O. Mauborgne - 1942 & 1961


These two etchings were made by Major General Joseph O. Mauborgne in 1942 and 1951. Both etchings were given to Colonel Albert R. and Florence Dreisbach in 1961. Colonel Dreisbach was the Director of Medical Research at the US Army Chemical Warfare Laboratories in Maryland. It was in the early 1960s that Dreisbach was in charge of the controversial testing of LSD and other drugs on unsuspecting US Army personnel.

The first etching is titled "Day of Rest - Fisherman's Wharf" and is edition 87/200. It is signed on the lower right "JOMauborgne '51". In the center is the note "To The Dreisbachs with best wishes for Christmas and the New Year - from the Mauborgnes." The back of the etching has a personal note from Joseph Mauborgne dated Mar. 1, 1961.

The second etching is titled "Burros" and is edition 36/75. It is signed on the lower right, "J.O.Mauborgne '42.” In the center is a personal note, "To Col. and Mrs. Dreisbach with best wishes for Xmas from the Mauborgnes '61." The back of the etching has a news clipping hand dated "January 1966." The clipping shows a picture of several people, including Maj. Gen. Mauborgne, in front of the computer and control displays for the first operational anti-ballistic missile system, called Project Nike.

Copyright © 2016 by Ralph Simpson - Creative Commons Attribution 4.0 International License