The ability to relay messages secretly has been a challenge throughout history. How can one person communicate secretly, efficiently, and across any distance without the information being discovered by someone other than the recipient? From the Greek scytale and the Roman Caesar Cipher, the technology of cryptography remained relatively the same until the late 17th century, when events in Europe and America required an updated message transmission method. 

Thomas Jefferson described his thirty-six cylindrical wheel cipher, a revolutionary idea in cryptography, as a secure means of transmitting information quickly and securely over long distances instead of relying on messengers. So what caused Thomas Jefferson to need a new means of communication? His invention, never constructed, relied on a simple design independently rediscovered and used during World War II. 

Invisible ink, secret codes, decoder rings, and the 1949 cereal box prize of Captain Midnight’s Key-O-Matic decoder are all examples of how secret communications fascinated the youth of the 19th century.[1] The atmosphere of the Cold War enhanced the allure of sharing messages with a friend that only they could read and only without the instrument necessary for deciphering. Although this technology appears archaic today, the history of cryptography dates back thousands of years, with much of the technology developed from the same conceptual ideas. Today's technology relies upon encryption and security, from bank account numbers to military messaging, and the basic concept remains the same. From the early Greek and Roman society to World War II, the field of cryptography evolved from the need for secrecy in communications to the need for secrecy in financial transactions.  

In Colonial America, the British military benefited from years of cryptography experience. The success of the American Revolution recognized a need for secure correspondence. Even before the Revolution, colonists found ways of secret communication that only increased in need as the American Revolution continued. Both sides used different forms of cryptography with varying success, with the Americans lagging behind the British in technology. France, Germany, and Britain all had divisions of ciphers working to decipher information quickly.

In America, Benjamin Franklin and Thomas Jefferson recognized that a new means of secret communication was necessary even before the revolution. Both had the advantage of exposure to numerous European ideas and new attempts at basic cryptography. Culminating with Thomas Jefferson inventing a new cipher device, the Jefferson cipher wheel, that was later the basis for several similar independent inventions, how was this idea simple enough to be rediscovered several times with much of the original idea used in the Korean War? Was his idea revolutionary or merely common-sense cryptography? Simple ideas with only tertiary connections could often lead to new discoveries of independent ideas and inventions.    

            The primary focus of cryptography is safeguarding messages from one source or individual to another source or individual that is only legible by the intended recipient.[2] Original messages are transformed into coded text and then delivered to the recipient. If the recipient owns the physical cipher or information necessary to decode the message, the message is translated back into the original form. Ideally, anyone intercepting the message will only see unintelligible information. Cryptography has changed the outcome of numerous military conflicts and protected secrets throughout history. The field of cryptanalysis, or the study of breaking codes, has impacted history through understanding lost languages and guided electronic communications in internet encryption. Cryptanalysis became increasingly necessary as cryptography increased in success.

            Cryptology was only sometimes regarded as vital. Messages relayed from one person to another through couriers remained influential until the realization that carriers could be corrupted or intercepted. The legend of one original cryptogram surrounds the death of Semiramis, a Persian queen. Instructions were inscribed on her tomb on her death with a cryptic message. Although this message kept gravediggers at bay, one curious man deciphered the code to reveal instructions on where to find her treasure. Outside the treasure box was another code, and once deciphered, the man opened the box. Inside was another inscription with another message promising wealth if the final cipher could be decoded. Unfortunately, this cipher was only a jumble of useless letters.[3] Communication at a distance is an idea that originated with the first people having anything worth comminating.[4]

            The basic design of cryptography began with ciphertext or simple substitution. The origin and usages are unknown, but the concept is relatively simple. Each letter has a corresponding symbol or a different letter. For example, shifting the alphabet to 1 letter left or right produces a simple ciphertext. The word for DOG would be transcribed as EPH. Simple to create and simple to design, it is also simple to decipher. Although it seems archaic, all future cryptographical writing is based on this concept, with advancements in how to shift letters to decrease readability to ensure security in correspondence. This includes modern cryptography and the ability to transmit electronic messages without detection. In addition, the basic concept of passcodes is also based on using a crypto "key" for entry.

The Egyptians used encryptions as early as 4000 years ago on the tomb of Khnumhotep II. Scribes carved hieroglyphs on his tomb, recording the details of his life. Unfortunately, some of the hieroglyphs did not match the meanings of obscure translations. In this way, Egyptians used encryption to protect knowledge instead of protecting correspondence.[5] In addition, it was also used to disguise inappropriate language or taboos.

The scytale was one of the most straightforward and earliest tools used in cryptography, initially by the Greeks. Although the exact date of invention is not known, there are mentions of the scytale in writing by Archilochus in the 7th century BC. Unlike later cipher inventions, the scytale did not change the original message. Instead, the message was written on parchment strips wrapped around a baton or rod with one letter in on each visible portion. The message was then unwrapped from the rod and delivered to the recipient. The recipient would wrap the scytale on a rod with the correct circumference, and the message would become legible. Only knowing the correct circumference of the rod would produce the original message.[6]  

Practical and straightforward, it also had the drawback of limited encryption. Through trial and error, intercepted scytales could be deciphered with trial and error with a collection of different size rods. The use of the scytale in military communications is debated based on the ease of decryption and lack of mention in early writings. The primary user may have only been to verify messages to avoid false relayed information.

            The Caesar Cipher, named after Julius Creaser, who used it in communications, was the first recorded cipher to use an alphabet shift to create secret correspondence in large quantities. Shifting letters in the alphabet only required the recipient to know the number of shifts. For example, instead of starting with ABCD, the alphabet would start with DEFG in a 4-letter shift. A would equal D, B would equal C, and so forth. This simple design is one of the most repeated designs, and mechanical variations formed the basis for later cryptography devices, including the Jefferson cipher wheel and the M-95 military cipher. A direct derivative of the Caesar Cipher is the modern ROT13 system. The ROT13 system, consisting of a 13-shift character system, was used in Netscape Communicator in 1999.[7]

            The Achilles heel of the Caesar Cipher was the ease of breaking the code. By counting the number of letters used the most in a language, the reader could logically make inferences about some letters. For example, the letter E is most used in the English alphabet. Therefore, logically, the highest number of repeated uses of a letter would correspond with E. By the 15th century, the homophonic substitution cipher solved this issue by assigning different characters to letters based on the percentage of use. For example, the letter E is used in 11% of the words in the current Oxford English Dictionary, and thus 11 different symbols are chosen at random to represent E. The letter O is used 7% of the time and would be symbolized by one of 7 different symbols. This method was popular during the Renaissance in communications between royalty, but the message was slow to decipher. [8] The interest in cryptography did expand during the Renaissance from only a military or government tool to the use by bankers and merchants. Increased economic trade made it necessary for banking to embrace cryptography for protection.

            Giovan Battista Bellaso, an Italian cryptologist, first conceived of a code that required the recipient to have a code to translate encrypted messages.[9] The critical design added security to secret documents if the key was not discovered. His autokey cipher incorporates the key in one phrase. The key can be derived from the text with knowledge of one agreed-upon letter, or it can be derived from a combination of letters. Simple in design, it lacked the security necessary to be popular in military correspondence.

            As the 15th century progressed, the need to translate secret messages increased. At the same time, Rome and Milan continued to use alphabetically shifted communications with trained scribes to quickly translate messages; Florence, born Leon Battista Alberti, combined letter shifting with cylindrical wheels. First postulated in Al-Qalqashandi during the 14th century, Alberti's polyalphabetic substantiation cipher used multiple alphabets and numerous substitutions to create messages quickly. The recipient needed the correct corresponding key. This key allows the recipient to arrange the disks like the user and translate the message. The principal of Alberti's polyalphabetic cipher disk, first used in 1476, was the basis of numerous future cryptography devices. Alperti’s device was the first simple mechanical hand-operated or manipulated device defined as a modern recognizable cipher device.[10]

            In the 16th century, Giovan Battista Bellaso expanded on the Trimethius cryptology table. This complex table enhanced Alberti's polyalphabetic cipher disk. Balise de Vigenere, a French diplomat, created a stronger autokey cipher in 1596 from a description of Bellaso’s device named the Vigenere cipher. This remained the standard European device for encryption with few adaptations for several years. During the Civil War, the Confederate States of America used a brass cipher disc that implemented the Vigeneres cipher design.[11]. 

            Increased conflicts in Europe presented a new problem for cryptography. It also increased the need for new technology and code breakers. Longer distances of communication delayed message delivery and more opportunity for interception. During the siege of Realmont by the Huguenots in 1628, a coded message was intercepted and deciphered. This message revealed the lack of ammunition by the Huguenots and hastened the defeat of the Huguenots. Recognizing the need for code-breaking as a means of war, European nations expanded agencies to decipher messages and increase the security of current devices for encryption. The greater the distance, the longer the time for correspondence to reach the intended recipient and the more time possible for interception and decoding.

            Although numerous European countries embraced cryptography, the British were the first to lead the way in deciphering agencies. The Napoleonic Wars highlighted the difficulties with early cryptography technology. During the Napoleonic Wars, the British intercepted and broke so many codes from the French that the embarrassed Napoleon ordered the military to create a new and unbreakable code. The Army of Portugal Code, first used in 1811, was broken in less than two days by the British. The second inclination of the Army of Portugal Code was still based on the early cipher wheel but increased the number of combinations to 1400. The added complications initially decreased the ability to break the code, but the complexity led many senders to leave portions unencrypted and thus easily deciphered within the year. The issue of working technology over the ease of use negated any benefits.  

            During the Revolutionary War, the Americans benefited from having intimate knowledge of French, British, and German cryptography. They also had the advantage of recognizing new directions in advanced messaging. Having been directly or indirectly involved in numerous European conflicts and embedded in Europe's diplomatic world, the Americans not only had access to the technology but also knowledge of the shortcomings of cryptography technology. Even though better technology was available, the Americans and the British initially relied on simple techniques to ensure correspondence was secret. Neither the British nor the Americans used the most advanced technique available.[12] Initially, it was up to amateurs leading the Continental Army to create systems of secret correspondence. However, lessons learned during the European conflicts and in the Napoleonic Wars gave cause to step back advancements in cryptography in exchange for simple, reliable techniques of secret correspondence.

            One of the most used forms of secret writing employed by the British and the Americans contained invisible ink. Invisible ink or sympathetic ink can be traced to the 4th century BC.[13]  Unlike the modern chemical inclination of invisible ink, the process during the American Revolution consisted of writing between lines of innocuous correspondence in a formula of sulfate and water. Adding heat to the paper revealed the messages between the somewhat innocent-looking correspondence. Later, sodium carbonate could be added to the letter instead of heat to expose the secret message. Employed overwhelmingly by George Washington in pamphlets, almanacs, and even bank books by his agents, both the Americans and British became quick to use heat or chemicals on all documents to expose messages and thus the technique was not an overwhelming success. Even unofficial documents were routinely heated or treated with chemicals to ensure secret messages were not escaping the military.

            The British also enhanced secret messaging by simply writing sensitive information, not coded, on tiny pieces of paper and then rolling them up small enough to fit into innocuous items like a spoon handle, a button, or a silver ball. The silver ball would be stored with musket balls and could be easily swallowed in the event of capture. This was effective but not practical as the Americans learned to search for items, and one British Spy, Daniel Taylor, was caught swallowing the ball after he was captured and threatened with forced extraction by bayonet until he voluntarily vomited to avoid a painful death. The Americans also used this technique but relied more on letter masking.[14] Letter masking consisted of letters containing hidden messages that could be decoded if the user had the proper mask to cover the page. A heart, hourglass, or other shape cutout was placed over the letter only to expose the vital text. This required an exorbitant amount of time to write for the letter to make sense to a reader while not giving away significant portions to the recipient.[15]

            One of the early cipher techniques in the American Revolution began as a simple monoalphabetic cipher incorporating a sentence or paragraph long enough to contain the 26 letters of the alphabet at least once.          This creates a mixed sequence of letters containing a passage used as a key. One surviving example is a letter from James Lovell, a Committee on Foreign Affairs member, to John Adams in 1871. Lovell suggested the key as the "first sixth part of that Family name where you and I spent our last evening with your lady before we set out on our journey hither.” [16] The resulting key is CR from the name Cranch.

            The numerous written techniques for secret correspondence increased as the American Revolution continued, and nothing was standardized. This led to frequent messages by the Americans and the British being misread. The danger of weak cryptography is discovery and poor translation leading to incorrect or vague messages. In 1775 the Continental Congress recognized the need for a committee to explore means of secret correspondence. Renamed the Committee for Foreign Affairs in 1777, one of the tasks was to standardize information. Robert Livingston, a delegate from New York, had used a private cipher to communicate with the Spanish court. His cipher, a two-part code, used numbers on one side with letters, words, or syllables on the opposite side. A random word written adjacent to the numbers created a new code on the opposite side. Many examples still in existence demonstrate how letters were written with a combination of encryption and unencrypted to save time.[17]Robert Livingston's code list became famous in 1781. 

            Benjamin Franklin, always tinkering with new ideas, also understood the need for secure correspondence.[18] Franklin entered the world of cryptography through a friendship with Charles Dumas.[19] Dumas maintained a residence in the Netherlands during the American Revolution and corresponded regularly with Franklin to show his support for the American cause. During this time, Franklin asked Dumas to spy for the Americans. Unfortunately, his reply could not be deciphered by anyone at the State Department because Dumas used popular French prose to create the cipher. Using a two-part sheet, the first page listed letters and symbols, and the second page listed numbers corresponding to the letter or symbol.[20]  The 682-character length provided several options for commonly used letters.

George Washington relied on invisible ink or a sympathetic stain to write between lines of letters.[21] He also used aliases and codes to conceal information on members' identities.[22] The Culper Ring, a network of spies organized by Benjamin Tallmadge and General George Washington, provided information on the operations of the British Army in New York City.[23] The exposure of Benedict Arnold was discovered through this operation.[24] His correspondence was handwritten and easily deciphered.[25] George Washington’s reliance on invisible ink led him in seeking new chemicals impervious to heat exposure.[26] James Jay, appointed to the New York State Assembly in 1778, invented two new invisible ink fluids that appeared white until treated with a second fluid making invisible ink more practical and increasing George Washington’s reliance on this form of secret writing in correspondence.[27] Attempts were made to standardize after the United States adopted the Constitution in 1789. This official cipher contained 1600-digit codes based on English syllables instead of letters.[28] It was not widely used and was unpopular. The difficulty of use and lack of interest led it to be discontinued in 1815.   

 

            George Washington knew firsthand the power of decoding messages and the disaster of information gained by the enemy. During the American Revolution, Washington received information from Yorktown that was deciphered but discovered that the information was too old to be of use. Understanding the need for current information and recognizing that the British used the same cipher, he quickly could decipher captured information based on outdated correspondence ciphers.[29]

            As George Washington's secretary of state, Thomas Jefferson primarily relied on hand-carried messages delivered by couriers. This included sensitive letters. It was not until he became minister to France in 1784 that he acknowledged the need for additional security. It was common practice for European postmasters to open any diplomatic letters or suspected correspondence. Jefferson continued to rely on invisible ink and code lists throughout his tenure. The discovery of a more secure ink by John Jay made Jefferson recognize a new and more secure method was needed. He also wanted something easier to use while being simple enough for messages to be written quickly and the recipient to decipher rapidly with little error. 

The wheel or cylindrical cipher, postulated in the 14th century and used during the 15th century, remained primarily forgotten or, at minimum, relegated to the lack of use due to the lack of interest in spending valuable time on a new means of secret communication when more straightforward methods were available. Simple in design and usage, it was quickly discovered when combined with the knowledge of letter-shifting techniques. Although Vigenère’s disk was a physical cipher device, it was not widely used then and was forgotten.

            Thomas Jefferson had a keen interest in science and inventions.[30] With little knowledge of cryptography beyond his exposure to letter shifting, invisible ink, and table coding, he created a device based on shared knowledge, common sense, and necessity. Understanding the minimal basics, Jefferson wrote about a new device that combined table coding and letter shifting with a physical device. The Jefferson Disk or “wheel cipher” was discovered by a researcher in 1922 while looking through original writings.[31]  Consisting of 36 wheels centered around an axle, each of the wheels contained a different random alphabet on the outside. Physically, Jefferson's wheel cipher resembled Vigenère’s disk.[32]  Both contained a 36-character keyword. However, the disks on Jefferson’s wheel cipher contained different random alphabets, while Vigenère's disk contained the same substitution alphabet on each. In addition, Jefferson's wheel cipher arranged the wheels simultaneously along the axes instead of serially like Vigenère's. This allowed the user to communicate securely with others with different wheel arrangements. 

            Using Jefferson’s wheel cipher required the sender to arrange the disks in an agreed-upon wheel order. The sender would spin each disk to spell the first 36 letters of a message. What appeared on the disk would be the message in one line and random letters on all other lines. Knowing the correct order of the disks, the sender could spin the wheel to spell out the random letters in one row, and the message would appear in another. The code could be deciphered only by knowing the correct order to place the wheels. As discovered by Jefferson, the key was the increased mathematical possible combinations. This combination of 36 wheels created fewer combinations than the three-wheel Enigma machine of World War II.[33]

            There is no evidence that Jefferson knew Vigenère's disk, but the similarity in design logically followed a simple design easily replicated and rediscovered.[34]  Before the Roman scytale, the Chinese also created a similar device used as a locking mechanism, and Jefferson may have seen a Chinese combination lock or read about it. However, the only evidence is Jefferson's subscription to a magazine containing an article on the Chinese combination lock which became popular in 1790s France.

            The idea of the Chinese combination lock was first used in 13th century China and is remarkably like all cylinder ciphers. Consisting of a central axis surrounded by cubes or rings inscribed by characters, the user unlocks the device by using the proper sequence of codes to align openings in the outer cubes or rings and releasing the lock. Even the locking mechanisms of today are based on the same concept of this Chinese combination lock.   

            When Jefferson became president, he chose the Vigenère cipher for the Lewis and Clark expedition and continued to use table cryptology throughout his political career. However, Jefferson's lack of a background in cryptography probably led to his inability to recognize his device as superior to existing table ciphers or, at a minimum, too new to implement in a system already in place. He also would have faced resistance in the military usage of a new device during a time when the need for secret correspondence was not as prevalent as during the American Revolution.

            Jefferson’s creation of a physical wheel cipher from his notes into a working prototype is absent in any surviving records. However, a similar wheel cipher was discovered near Jefferson's home in Monticello. Although it functioned precisely as Jefferson designed, the device discovered contained 40 characters in French on each wheel and holes in each disk to maintain the wheel positions after the correct order was achieved. This is like Jefferson’s notes but contains numerous variations not mentioned. 

            The uniqueness of the wheel cipher also overshadows the simplicity of the design. Unlike other inventions, the wheel cipher was invented, forgotten, reinvented, forgotten, and invented again independently! Some of this may be attributed to being forgotten due to the lack of usage between military conflicts, only to be rediscovered as the need increased. If the technology of secret correspondence continued to work efficiently, new designs would slowly gain acceptance. Table cipher technology remained relatively unchanged and valuable; thus, the need for advanced cryptography was unnecessary. However, when it was necessary to increase secure transmissions, the mathematical combination possibilities of the cipher wheel, ease of usage, and readily available material inspired others to rediscover the technology.

            In 1891, a French military cryptanalyst also formulated plans for a cipher wheel independently from Jefferson's design. Born in 1846, Étienne Bazeries was a French military cryptanalyst during WWI.[35]  Considered a brilliant cryptanalyst and understanding the need for a mathematically challenging code, Bazeries combined the knowledge of cryptography with a physical wheel to create the Great Cipher.[36]  Bazeries’ cipher used 20 or 30 disks sharing a standard axle with random numbers, symbols, and letters on the outside.[37]  Unlike Jefferson’s wheel cipher, Bazeries’ cipher had the advantage of being produced in large numbers during a time when the necessity of secure communication also competed with new electronic telegraph communications, and Bazeries’ cipher was easily and securely used in long distant transmissions. The difficulty in breaking codes after using Brazeries cipher led to forming of independent military organizations tasked with code breaking and disseminating information.[38]

            During the Civil War, independent discoveries of cryptography reverted to alphabetical shifts as a means of communicating. For example, Albert Myer developed a method of relaying messages using signal flags, or flag telegraphy, using letters, directions, and combinations. Another device, possibly used during this time, was Bolton's Cipher Wheel. Although little is known about the inventory, it consisted of only one wheel and an inner ring as a decryption device.[39] Also simple in use, the basic design is not unremarkable compared to Jefferson’s wheel cipher with one disk and a center decoder instead of numerous disks on a central axis.  

The M-94, adopted by the United States Army in 1922, modernized cryptography into the 20th century.[40]  Although adapted in 1922, the same year Jefferson’s wheel cipher papers were discovered, it was independently conceived by Colonel Parker Hitt in 1917 and developed by Joseph Oswald Mauborgne.[41]  Like Jefferson's wheel cipher, the M-94 contained disks attached by a central rod. Each disc, 25 in total, contained random Roman alphabet letters.[42]  The only exception was the 17th disk that contained the letters arranged to spell ARMY OF THE US before the remaining 16 random letters. Made of aluminum, the M-94 was lightweight, sturdy, and easily assembled. Unlike Jefferson's wheel cipher, the 25 disks made it possible only to encode 25 letters simultaneously. One advantage of the Hitt cipher wheel was its small size. A little more than 4 inches in length, it was easily concealed and transported in a pocket. Using the M-94 required little experience, and more than 9000 were produced between 1921 and 1943. 

The U.S. Navy also adopted the M-94 under the name CSP 488 without the ARMY OF THE US disk and instead contained a random letter disk in its place.[43] Also invented during this time was the M-138, which used strips of cardboard on a flat surface with the same concept as aluminum shortages required a change in design.[44]  These designs continued to be standard cipher equipment through the mid-1940s, when the mechanical M-209, based loosely on the same concept, remained in use through the Korean War.[45] Also easily used, small enough to fit into a pocket, and durable, the 150000 M-209's were produced. This standardization and ease of use led to the military requiring personnel to be trained on the essential use of standard communication.[46] 

            The culmination of cipher wheel technology yielded the Enigma machine used by Nazi Germany. Although still based on the simple concept of coded wheels, the Enigma machine is unlike any previous concepts. The Enigma machine effectively ended the rediscovery of previous cryptography technology, yet many of the simple concepts are still recognizable in parts of the machine.

             Thomas Jefferson's cipher wheel may not have been recognized at the time as a revolution in cryptography. However, just as earlier designs were lost and rediscovered, the Jefferson cipher wheel demonstrated the ability of simple designs and logic to continue the process of reinvention. Had his invention been created and used, later cryptography devices would have been heralded as improvements on his design. Instead, the common thread remains that the need for secure communications throughout history has maintained relationships with previous ideas, often simple in design and easily discovered.

            Physically, all the cipher devices from Alberti’s polyalphabetic cipher disk to the M-94 have parts easily recognizable and simple to construct. The material and language may be different, but the concept of a wheel to shift letters is such a standard design that the independent rediscovery of the operational use spanned generations. Even with the similarities to other devices, Thomas Jefferson could easily have discovered his invention independently. The common thread between all cryptography is the need for secrecy, and as time progressed, so did the need for additional methods of secret correspondence. The waning and waxing of these inventions and rediscovery corresponded with the increased need. Simple logical technology made it possible.

 

 

 

 

 

 

 

 

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