World War II cryptography

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Cryptography was used extensively during World War II, with a plethora of code and cipher systems fielded by the nations involved. In addition, the theoretical and practical aspects of cryptanalysis , or codebreaking, was much advanced.

Cryptography practice and study of techniques for secure communication in the presence of third parties

Cryptography or cryptology is the practice and study of techniques for secure communication in the presence of third parties called adversaries. More generally, cryptography is about constructing and analyzing protocols that prevent third parties or the public from reading private messages; various aspects in information security such as data confidentiality, data integrity, authentication, and non-repudiation are central to modern cryptography. Modern cryptography exists at the intersection of the disciplines of mathematics, computer science, electrical engineering, communication science, and physics. Applications of cryptography include electronic commerce, chip-based payment cards, digital currencies, computer passwords, and military communications.

World War II 1939–1945 global war

World War II, also known as the Second World War, was a global war that lasted from 1939 to 1945. The vast majority of the world's countries—including all the great powers—eventually formed two opposing military alliances: the Allies and the Axis. A state of total war emerged, directly involving more than 100 million people from over 30 countries. The major participants threw their entire economic, industrial, and scientific capabilities behind the war effort, blurring the distinction between civilian and military resources. World War II was the deadliest conflict in human history, marked by 50 to 85 million fatalities, most of whom were civilians in the Soviet Union and China. It included massacres, the genocide of the Holocaust, strategic bombing, premeditated death from starvation and disease, and the only use of nuclear weapons in war.

Code (cryptography)

Cryptography in simple terms means the use of any alphabet or numerical statement which has a meaning or stores a message.


Probably the most important codebreaking event of the war was the successful decryption by the Allies of the German "Enigma" Cipher. The first complete break into Enigma was accomplished by Poland around 1932; the techniques and insights used were passed to the French and British Allies just before the outbreak of the war in 1939. They were substantially improved by British efforts at the Bletchley Park research station during the war. Decryption of the Enigma Cipher allowed the Allies to read important parts of German radio traffic on important networks and was an invaluable source of military intelligence throughout the war. Intelligence from this source (and other high level sources, including the Fish ciphers) was eventually called Ultra. [1] [2] [3]

Cryptanalysis of the Enigma ciphering system enabled the western Allies in World War II to read substantial amounts of Morse-coded radio communications of the Axis powers that had been enciphered using Enigma machines. This yielded military intelligence which, along with that from other decrypted Axis radio and teleprinter transmissions, was given the codename Ultra. This was considered by western Supreme Allied Commander Dwight D. Eisenhower to have been "decisive" to the Allied victory.

Bletchley Park British country house

Bletchley Park is a nineteenth-century mansion and estate near Milton Keynes in Buckinghamshire, constructed during the years following 1883 for the English financier and politician Sir Herbert Samuel Leon in the Victorian Gothic, Tudor, and Dutch Baroque styles, on the site of older buildings of the same name. It has received latter-day fame as the central site for British codebreakers during World War II, although at the time of their operation this fact was a closely guarded secret. During the Second World War, the estate housed the British Government Code and Cypher School (GC&CS), which regularly penetrated the secret communications of the Axis Powers – most importantly the German Enigma and Lorenz ciphers; among its most notable early personnel the GC&CS team of codebreakers included Alan Turing, Gordon Welchman, Hugh Alexander and Stuart Milner-Barry.

Military intelligence is a military discipline that uses information collection and analysis approaches to provide guidance and direction to assist commanders in their decisions. This aim is achieved by providing an assessment of data from a range of sources, directed towards the commanders' mission requirements or responding to questions as part of operational or campaign planning. To provide an analysis, the commander's information requirements are first identified, which are then incorporated into intelligence collection, analysis, and dissemination.

A similar break into the most secure Japanese diplomatic cipher, designated Purple by the US Army Signals Intelligence Service, started before the US entered the war. Product from this source was called Magic.

In the history of cryptography, "System 97 Typewriter for European Characters" or "Type B Cipher Machine", codenamed Purple by the United States, was a diplomatic cryptographic machine used by the Japanese Foreign Office just before and during World War II. The machine was an electromechanical stepping-switch device using a 6 X 25 substitution table.

Magic was an Allied cryptanalysis project during World War II. It involved the United States Army's Signals Intelligence Service (SIS) and the United States Navy's Communication Special Unit.


Central Bureau

The Central Bureau was one of two Allied Signals intelligence (SIGINT) organisations in the South West Pacific area (SWPA) during World War II. Central Bureau was attached to the Headquarters of the Allied Commander of the South West Pacific area, Douglas MacArthur. Central Bureau's role was to research and decrypt intercepted Imperial Japanese Army traffic and work in close co-operation with other SIGINT centres in the USA, United Kingdom and India. Air activities included both army and navy air forces, as there was no independent Japanese Air Force.

Fleet Radio Unit, Melbourne (FRUMEL) was a United States–Australian–British signals intelligence unit, founded in Melbourne, Australia, during World War II. It was one of two major Allied signals intelligence units, called Fleet Radio Units, in the Pacific theatres, the other being FRUPAC, in Hawaii. FRUMEL was a US Navy organisation, reporting directly to CiCPAC in Hawaii and the Chief of Naval Operations in Washington, and hence to the central crypographic organization. The separate Central Bureau in Melbourne was attached to MacArthur's Allied South West Pacific Area command headquarters.

Fleet Radio Units (FRU) were the major centers for Allied cryptological and signals intelligence during the Pacific Campaign of World War II. Initially two FRUs were established in the Pacific, one at Pearl Harbor, Hawaii, called Station HYPO or FRUPAC, and the other, called Station CAST or Belconnen, at Cavite Naval Yard, then Corregidor, Philippines. With the fall of the Philippines to Imperial Japanese forces in April and May 1942, CAST personnel were evacuated to a newly established FRU at Melbourne, Australia, called FRUMEL.




Fish (cryptography) Allied codename for any of several German teleprinter stream ciphers used during World War II

Fish was the UK's GC&CS Bletchley Park codename for any of several German teleprinter stream ciphers used during World War II. Enciphered teleprinter traffic was used between German High Command and Army Group commanders in the field, so its intelligence value (Ultra) was of the highest strategic value to the Allies. This traffic normally passed over landlines, but as German forces extended their geographic reach beyond western Europe, they had to resort to wireless transmission.

Lorenz cipher

The Lorenz SZ40, SZ42a and SZ42b were German rotor stream cipher machines used by the German Army during World War II. They were developed by C. Lorenz AG in Berlin. The model name SZ was derived from Schlüssel-Zusatz, meaning cipher attachment. The instruments implemented a Vernam stream cipher.

The Short Weather Cipher, also known as the weather short signal book, was a cipher, presented as a codebook, that was used by the radio telegraphists aboard U-boats of the German Navy (Kriegsmarine) during World War II. It was used to condense weather reports into a short 7-letter message, which was enciphered by using the naval Enigma and transmitted by radiomen to intercept stations on shore, where it was deciphered by Enigma and the 7-letter weather report was reconstructed.



Japanese army and diplomatic codes. This article is on Japanese army and diplomatic ciphers and codes used up to and during World War II, to supplement the article on Japanese naval codes. The diplomatic codes were significant militarily, particularly those from diplomats in Germany.

The vulnerability of Japanese naval codes and ciphers was crucial to the conduct of World War II, and had an important influence on foreign relations between Japan and the west in the years leading up to the war as well. Every Japanese code was eventually broken, and the intelligence gathered made possible such operations as the victorious American ambush of the Japanese Navy at Midway (JN-25b) and the shooting down of Isoroku Yamamoto in Operation Vengeance.


Soviet Union


United Kingdom

United States

See also

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  1. Budiansky, Stephen (2000). Battle of Wits: The Complete Story of Codebreaking in World War II. Simon and Schuster. ISBN   9780684859323.
  2. Hinsley, F. H.; Stripp, Alan (2001). Codebreakers: The Inside Story of Bletchley Park. Oxford University Press. ISBN   9780192801326.
  3. Haufler, Hervie (2014). Codebreakers' Victory: How the Allied Cryptographers Won World War II. Open Road Media. ISBN   9781497622562.