Ciphering has always been considered vital for military and diplomatic secrecy. Empires and nations have frequently owed their existence to the security of their communications, as information that falls into the wrong hands can give an enemy a crucial advantage.
Historians believe that the deciphering of the German Enigma codes by British intelligence at Bletchley Park in World War II played a key role in the allied victory. Indeed, the Allies went to great lengths to prevent the Germans from discovering that the Enigma had been broken. For instance, when the British discovered the locations of five German tankers refueling submarines in the Atlantic, they sank only three. If the British had taken out all five tankers, the Germans might have become suspicious.
Is cryptography a weapon? Its relation to military operations seems to be rather that of a support function. An army needs jeeps, radios, food and clothes, just as it needs a way to report observations, and receive orders, that cannot be overheard by its rivals.
Here are a few historical events where cryptography had played an important role. The Spartans of Greece created the first military form of cryptography. They used a system which consisted of a thin sheet of papyrus wrapped around a staff (known as a skytale). This was used in the 5th century B.C. to send secret messages between Greek warriors. The secret key of the text is the circumference of the wood. With the wrong circumference, the message is unusable. If the wood matches, you are able to read the message.
In the latter part of the Middle Ages the use of secret writing increased. European cryptology dates from the Middle Ages, during which it was developed by the Papal States and the Italian city-states. The first brief code vocabularies, called nomenclators, were gradually expanded and became the mainstay for several centuries for diplomatic communications of nearly all European governments. In 1628, a Frenchman named Antoine Rossignol helped his army defeat the Huguenots by decoding a captured message. After this victory, he was called upon many times to solve ciphers for the French government. When Rossignol died in 1682, his son, and later his grandson, continued his work. By this time, there were many cryptographers employed by the French government. Together, they formed the "Cabinet Noir" (the "Black Chamber").
By the 1700's, "Black Chambers" were common in Europe, one of the most renown being that in Vienna. It was called 'The Geheime Kabinets-Kanzlei' and was directed by Baron Ignaz de Koch between 1749 and 1763. This organisation read through all the mail coming to foreign embassies, copied the letters, resealed them, and returned them to the post-office the same morning. The same office also handled all other political or military interceptions, and would sometimes read as many as 100 letters a day.
The English Black Chamber was formed by John Wallis in 1701. Until that time, he had been solving ciphers for the government in a variety of unofficial positions. After his death in 1703, his grandson, William Blencowe, who was taught by his grandfather, took over his position and was granted the title of Decypherer. The English Black Chamber had a long history of victories in the cryptographic world.
In the early history of the United States, codes were widely used, as were book ciphers. During the American Civil War (1861-1865) ciphers were not very complex. Many techniques consisted merely of writing words in a different order and substituting code words for proper names and locations. The Confederate Army primarily used the Vigenère cipher and on occasion monoalphabetic substitution.
In the beginning of the 20th century, war was becoming likely in Europe. During World War One, England spent a substantial effort improving its cryptanalytic capabilities so that when the war started, they were able to solve most enemy ciphers. The cryptanalysis group was called 'Room 40' because of its initial location in a building in London. Their greatest achievements were in solving German naval ciphers. These solutions were greatly simplified because the Germans often used political or nationalistic words as keys, changed keys at regular intervals and gave away intelligence indicators when keys were changed.
The United States had initially chosen to remain neutral during World War One (1914-1918). However, when Germany broke its pledge not to engage in submarine warfare, the United States decided to break all diplomatic relations with Germany. British cryptographers broke the Zimmerman Telegram (1917), a secret German communication to Mexico in which the Germans offered Mexico United States territory in return for joining the German cause. When the American public realised this, their opinion changed in favour of joining the war with the allies. It is believed that no other single cryptanalysis has had such enormous consequences as the deciphering of the Zimmerman Telegram.
The ADFGVX system was put into service by the Germans near the end of World War One. This was a cipher which performed a substitution (through a keyed array), fractionation and then transposition of the letter fractions. It was broken by the French cryptanalyst, Lieutenant Georges Painvin.
In 1939, Japan had started using their PURPLE code, one of the most complex codes of World War II. However the Americans (under the direction of Chief Cryptanalyst William Friedman) had great success at breaking Japanese codes. (The US Navy, having broken Japans' ORANGE and RED codes in the 1920's, had experience in the formal language used by the Japanese in their communications.) While the Japanese, unable to break US codes, assumed that their codes were also unbreakable.
The cracking of the Enigma machine used by the Germans during World War II is believed to be one of the greatest achievements in the field of cryptanalysis. The Enigma was an electrical enciphering machine (and looked like a typing machine), which provided better encryption of messages t han other machines at the time because of the concept of rotating rotors. Originally built for commercial use, it was soon put to use by the Germans for securing their radio communications during the War. They believed the machine to be invincible as the likelihood of breaking a message enciphered by the Enigma was too remote a possibility to consider.
The initial work on cryptanalysing Enigma began during peacetime by the Polish Cipher Bureau. They had managed to acquire a commercial Enigma, and three young mathematicians led by Marian Rejewski began to work on it. By early 1933, they had figured out the complex ciphers using a combination of math, statistics, computational ability and guesswork.
When the Second World War began, the Poles, realizing that a German invasion was imminent, handed over all the information to the British. The British cipher department later came to be known as the famous Bletchley Park. It was here that the young English mathematician, Alan Turing, started work on the Enigma. Turing, collaborating with another British mathematician Gordon Welchman, further enhanced this machine which came to be known as the Turing Bombe. This Bombe was in effect a collection of Enigma machines and this played a key role in the cracking of the Enigma cipher. This was the first recorded instance of an electro-mechanical device being used in cryptanalysis.
Fish was used by the German army in WWII to encipher high-command communications. It was produced by a stream cipher called the Lorentz machine. Fish was the name given to it by British cryptanalysts. It was important because it caused difficulties for British analysts, who finally developed a machine called Colossus, which was arguably the first, or one of the first, digital computers. The Colossus machine may have been an important factor in the planning and success of the Allied attack on Normandy. Given the intelligence produced by cryptanalysis of Fish, Allied forces knew the positions of pretty much every German division.