Cryptography (military communications)

Cryptography is the art of changing a message in a manner that makes it readable only to the intended receiver. Cryptography is composed of two arts: encoding or enciphering is the act of taking plain text and converting it to secret text. The intended receiver of the message is given a key that allows him or her to convert coded messages to plain text. Decoding or deciphering is the act of attempting to break the secret codes and uncover the original message.

There are two forms of encoding a message: substitution, which occurs when the letters of the plain text are replaced with other signs or symbols; and transposition, which retains the letters of the original plain text and merely changes the order in which they appear.

As military communication technology has increased in importance in the conduct of war, cryptography has become vital to military success. Nations that are able to securely communicate information are able to hide their strategy and strength from enemies, while those nations that can intercept and decipher communication of their enemies gain powerful strategic advantages.

Ancient Codes

Early evidence of governmental cryptography includes Homer’s Iliad (c. 800 b.c.e.; English translation, 1616), which tells of Proteus condemning Bellerophon to death through the use of a secret message. In Historiai Herodotou (c. 424 b.c.e.; The History, 1709), Herodotus recounts a number of tales of secret military messages, including Demaratus’s use of a message hidden under the wax on wooden tablets to warn the Greeks that Xerxes was planning an invasion.

By 487 b.c.e., the Spartans established the first military system of cryptography called the Skytale. This was a staff around which a length of leather was wrapped and then written upon. The leather strip was then unrolled and worn as a belt until the bearer reached the recipient who had a matching staff, allowing the message to be reconstructed.

Another Greek method was developed by Polybius (200-120 b.c.e.). Polybius arranged the letters of the alphabet in a five-by-five square. Rows and columns were numbered from one to five so that each letter in the square had a corresponding (row, column) pair of numbers that could easily be signaled by torches.

The first military use of substitution ciphers dates back to Julius Caesar. In Comentarii de bello Gallico (51-52 b.c.e.; translated with Comentarii de bello civili, 45 b.c.e., as Commentaries, 1609), Caesar recounts substituting the Greek alphabet for Latin in a message to Cicero, requesting reinforcement. Caesar later refined his substitution code, merely using the letter three letters ahead of the plaintext letter. As a result, all simple substitution codes are called Caesar alphabets.

Cryptography as a Political Science

The Arabic world was the first civilization to develop a full study of secret writing. Al-Khalīl, who wrote Kitab al-mu$amma (the book of secret language; this “lost book” is known only by mentions of the work in others’ writing), was inspired to write the work by his solution of a cryptogram sent him by the Byzantine emperor. Al-Khalīl knew that the message’s plain text likely began with a standard salutation (“In the name of God”). He used that knowledge as a key to the substitution code, a decryption method that was still being used in World War II. Another Arabic author, Qalqashandi, first wrote of frequency analysis, which works by recording the frequency of each cipher text symbol and comparing those frequencies to the frequencies of average letter usage in a language as a key to decipherment. For instance, if a coded message whose plain text is known to be English is broken down by symbol frequency, the symbol that appears most often is likely to represent the plain text letter “e,” the most common letter used in English. Frequency analysis is still used in decryption.

During the Middle Ages, the governments of Western Europe used codes to communicate with ambassadors. In 1379, while working for the antipope Clement VII, Gabreli di Lavinde compiled a collection of keys. Lavinde’s collection included the first known nomenclature, a code that combined substitution alphabets and codes. In 1452, Venice established the first organization whose sole purpose was to create ciphers for the government and decipher intercepted codes.

By 1446, Leon Battista Alberti published the first Western treatise on cryptography. He also developed a form of cipher known as polyalphabetic substitution by designing a metal disc that had an outer ring with one alphabet and a movable inner ring with a second alphabet. The inner ring could be moved to create one of a large number of possible substitution alphabets. This encryption is made stronger by moving the ring to a new setting after a set number of words. He then developed the most secure encryption to that date, the enciphered code. Enciphered code was created by assigning numerical codes to a set of words and then using the disc to further encipher the numbers. Alberti’s systems were used by governments and military leaders for the next four centuries.

Cryptography’s military importance grew. In 1628, during the Siege of Realmont, Henry II, the prince of Condé, had surrounded the town and was preparing to begin to try to drive the Huguenots into surrender. The Huguenots refused to surrender and shelled Condé’s forces with cannons. Henry’s men captured an enciphered Huguenot message, which Condé sent to Albert Rossignol, who quickly solved the cipher. The message stated that if munitions could not be supplied quickly, the Huguenots would have to surrender. Condé returned the deciphered message to the Huguenots, who promptly surrendered.

Rossignol became France’s first full-time cryptologist. The work of Rossignol and his son proved so important to the French military that the government put a group of cryptanalysts into place as the Cabinet Noir, the first Black Chamber, which regularly read and decrypted diplomatic and military dispatches through the 1700’s. Their British counterparts were known as the Deciphering Branch.

Revolutions in Cryptography

British spy cryptography was strong during the American Revolution, but it was surpassed in importance by two U.S. agents, Samuel Woodhull and Robert Townsend, who used invisible ink and a nomenclature to supply Washington with critical military intelligence.

U.S. cryptanalysis was fathered by James Lovell, a member of the Continental Congress, who had also deciphered captured British messages. Lovell’s greatest success came in 1781 when he deciphered a message between Lord Cornwallis, Britain’s second in command in America and his superior, General Henry Clinton. Cornwallis had moved his forces to Virginia in hopes of retaking that colony and crushing the rebellion. The message revealed that Cornwallis was in desperate need of reinforcement. The United States took this information and successfully blockaded Cornwallis, forcing his eventual surrender.

In 1795, Thomas Jefferson invented a new military cipher system. Jefferson’s wheel cipher consisted of a set of wheels, each of which contained a random ordering of the alphabet. Messages were encoded and decoded by aligning the wheels along the axle until the desired message was formed. Decryption required the receiver to have an identical set of wheels and knowledge of the correct alignment. During World War II (1939–1945), the U.S. Navy used a Jefferson wheel cipher called the StripCipher M-138-A.

In 1844, the telegraph changed the face of war. Through telegraphy, a commander could, for the first time, instantly communicate with field commanders during a battle. However, communication via telegraph is insecure, making cryptography essential.

The American Civil War (1861–1865) saw use of simple ciphers. However, Union cryptanalysts were often able to decipher Confederate ciphers before their intended recipient could. This provided the Union forces with a strategic edge in many critical situations.

World War I

The advent of radio telegraphy changed cryptography in 1895. Now, anyone with a radio receiver could intercept transmission. By the outbreak of World War I in 1914, the French had established a network of receivers that were able to intercept most of the German transmissions. This advantage was multiplied when, in 1914, England’s first offensive act of the war was to cut Germany’s transatlantic telegraph cables, forcing Germany to communicate with the world via radio or over cables controlled by its enemies.

England and its allies were rewarded for this maneuver by fate when in September of 1914 the German light cruiser Magdeburg was wrecked. From the wreck, the Russians recovered the cipher and signal books of the German navy. With this windfall and some insightful methods for recovering the keys, the British cryptanalysts, known as Room 40, were able to begin reading signals from the German navy. After the war, it was estimated that Room 40 had solved 15,000 encrypted German messages, none of which was more vital to winning the war than the Zimmerman telegram. In this instance, a telegram from German foreign minister Arthur Zimmerman urged Mexico to wage war on the United States in an attempt to keep the United States from entering the war. After being informed of the contents of the telegram, President Franklin D. Roosevelt terminated diplomatic relations with Germany, and three months later, he cited the Zimmerman telegram when he asked Congress to declare war on Germany.

The French counterparts to Room 40, working independently, were able to break the German U-boat codes as well as diplomatic messages between Germany and Spain. It was the latter that led to the execution of the beautiful dancer Mata Hari as a German spy.

World War II

Military dependence on radio communication meant that World War II was frequently a cryptographer’s war. The European Allied forces built strong cryptanalysis bureaus that enabled them to keep their leadership one step ahead of the Axis.

Meanwhile, U.S. cryptography was in such poor shape early in the war that Japan’s cryptanalytic group, the Ango Kenkyu Han (code research section) had broken nearly all of the U.S. diplomatic and military codes. The situation was so bad that when Roosevelt sent his personal appeal for peace to the Japanese emperor on December 6, 1941, the Japanese military intercepted the message, solved it, and detained it to frustrate any effort at peacemaking.

By June of 1942, Captain Lee W. Parke, a Navy cryptanalyst, was named chief of the new Division of Cryptography, finally securing U.S. communication. Within months, the United States had cracked JN-25, a Japanese naval code. As a result, the Americans deciphered Japanese admiral Isoroku Yamamoto’s plan to ambush the U.S. Pacific Fleet at Midway Island. Admiral Chester W. Nimitz concentrated his forces around Midway and held the island. This naval battle is pointed to as the turning point of the war in the Pacific. The United States did implement one code that remained unbroken during the war. The Navajo Code Talkers transmitted secure information, including messages referring to the development of nuclear weapons, in their native dialect, which was unknown to Axis cryptanalysts.

Technology Pushes On

Beginning in World War II, the computer has been the central character in the development of cryptography. Computers initially were used to develop rotor style polyalphabetic substitutions with enormous periods. On the analysis side, computers were used to run frequency analysis on cipher text faster and more efficiently than cryptanalysts.

By 1952, Harry S. Truman had created the National Security Agency (NSA) whose role includes establishing governmental codes and cryptanalysis. By 1977, the NSA had developed and adopted the Data Encryption Standard (DES). Although this system, which reduces plain text to binary bits of information and then encodes them, is very secure, the U.S. government retains the key for all DES systems. This means that DES encrypted messages are not secure from the U.S. government. The development of military cryptographic systems and cryptanalysis has become a function of computer programmers.

The Enigma and the Germans

Bibliography

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