Coral (cypher Machine)
   HOME

TheInfoList



OR:

The vulnerability of Japanese naval codes and ciphers was crucial to the conduct of
World War II World War II or the Second World War (1 September 1939 – 2 September 1945) was a World war, global conflict between two coalitions: the Allies of World War II, Allies and the Axis powers. World War II by country, Nearly all of the wo ...
, 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 in 1942 (by breaking code JN-25b) and the shooting down of Japanese admiral
Isoroku Yamamoto was a Marshal Admiral of the Imperial Japanese Navy (IJN) and the commander-in-chief of the Combined Fleet during World War II. He commanded the fleet from 1939 until his death in 1943, overseeing the start of the Pacific War in 1941 and J ...
a year later in
Operation Vengeance Operation Vengeance was the American military operation to kill Admiral Isoroku Yamamoto of the Imperial Japanese Navy on 18 April 1943 during the Solomon Islands campaign in the Pacific Theater of World War II. Yamamoto, commander of the Combine ...
. The
Imperial Japanese Navy The Imperial Japanese Navy (IJN; Kyūjitai: Shinjitai: ' 'Navy of the Greater Japanese Empire', or ''Nippon Kaigun'', 'Japanese Navy') was the navy of the Empire of Japan from 1868 to 1945, Potsdam Declaration, when it was dissolved followin ...
(IJN) used many
codes In communications and information processing, code is a system of rules to convert information—such as a letter, word, sound, image, or gesture—into another form, sometimes shortened or secret, for communication through a communication ch ...
and
ciphers In cryptography, a cipher (or cypher) is an algorithm for performing encryption or decryption—a series of well-defined steps that can be followed as a procedure. An alternative, less common term is ''encipherment''. To encipher or encode i ...
. All of these cryptosystems were known differently by different organizations; the names listed below are those given by Western cryptanalytic operations.


Red code

The Red Book code was an IJN
code book A codebook is a type of document used for gathering and storing cryptography codes. Originally, codebooks were often literally , but today "codebook" is a byword for the complete record of a series of codes, regardless of physical format. Cr ...
system used in
World War I World War I or the First World War (28 July 1914 – 11 November 1918), also known as the Great War, was a World war, global conflict between two coalitions: the Allies of World War I, Allies (or Entente) and the Central Powers. Fighting to ...
and after. It was called "Red Book" because the American photographs made of it were bound in red covers.Greg Goebel
"US Codebreakers In The Shadow Of War"
2018.
It should not be confused with the RED cipher used by the diplomatic corps. This code consisted of two books. The first contained the code itself; the second contained an additive cipher which was applied to the codes before transmission, with the starting point for the latter being embedded in the transmitted message. A copy of the code book was obtained in a "black bag" operation on the luggage of a Japanese naval attaché in 1923; after three years of work
Agnes Driscoll Agnes Meyer Driscoll (July 24, 1889 – September 16, 1971), known as "Miss Aggie" or "Madame X'", was an American cryptanalyst during both World War I and World War II and was known as "the first lady of naval cryptology." Early years Driscoll ...
was able to break the additive portion of the code. Knowledge of the Red Book code helped crack the similarly constructed Blue Book code.


Coral

A cipher machine developed for Japanese naval attaché ciphers, similar to JADE. It was not used extensively, but Vice Admiral
Katsuo Abe Katsuo (written: , , or ) is a masculine Japanese given name. Notable people with the name include: *, Japanese basketball player *, Japanese boxer *, Japanese boxer *, Japanese footballer *, Japanese sumo wrestler *, Japanese actor *, Japanese l ...
, a Japanese representative to the Axis Tripartite Military Commission, passed considerable information about German deployments in CORAL, intelligence "essential for Allied military decision making in the European Theater."


Jade

A cipher machine used by the Imperial Japanese Navy from late 1942 to 1944 and similar to CORAL.


Dockyard codes

A succession of codes used to communicate between Japanese naval installations. These were comparatively easily broken by British codebreakers in Singapore and are believed to have been the source of early indications of imminent naval war preparations.


JN-11

The Fleet Auxiliary System, derived from the JN-40 merchant-shipping code. Important for information on troop convoys and orders of battle.


JN-20

An inter-island cipher that provided valuable intelligence, especially when periodic changes to JN-25 temporarily blacked out U.S. decryption. JN-20 exploitation produced the "AF is short of water" message that established the main target of the Japanese Fleet, leading to a decisive U.S. victory at the
Battle of Midway The Battle of Midway was a major naval battle in the Pacific Ocean theater of World War II, Pacific Theater of World War II that took place on 4–7 June 1942, six months after Japan's attack on Pearl Harbor and one month after the Battle of t ...
in 1942.


JN-25

JN-25 is the name given by codebreakers to the main, and most secure, command and control communications scheme used by the IJN during World War II. Named as the 25th Japanese Navy system identified, it was initially given the designation AN-1 as a "research project" rather than a "current decryption" job. The project required reconstructing the meaning of thirty thousand code groups and piecing together thirty thousand random additives. Introduced from 1 June 1939 to replace Blue (and the most recent descendant of the Red code), it was an enciphered code, producing five-numeral groups for transmission. New code books and super-enciphering books were introduced from time to time, each new version requiring a more or less fresh cryptanalytic attack.
John Tiltman Brigadier John Hessell Tiltman, (25 May 1894 – 10 August 1982) was a British Army officer who worked in intelligence, often at or with the Government Code and Cypher School (GC&CS) starting in the 1920s. His intelligence work was largely co ...
with some help from
Alan Turing Alan Mathison Turing (; 23 June 1912 – 7 June 1954) was an English mathematician, computer scientist, logician, cryptanalyst, philosopher and theoretical biologist. He was highly influential in the development of theoretical computer ...
(at GCSB,
Government Communications Security Bureau The Government Communications Security Bureau (GCSB) () is the public service, public-service department of New Zealand charged with promoting New Zealand's national security by collecting and analysing information of an intelligence nature. Th ...
) had "solved" JN25 by 1941, i.e. they knew that it was a five-digit code with a codebook to translate words into five digits and there was a second "additive" book that the sender used to add to the original numbers "But knowing all this didn’t help them read a single message". By April 1942 JN25 was about 20 percent readable, so codebreakers could read "about one in five words" and
traffic analysis Traffic analysis is the process of intercepting and examining messages in order to deduce information from patterns in communication. It can be performed even when the messages are encrypted. In general, the greater the number of messages observ ...
was far more useful. Tiltman had devised a (slow; neither easy nor quick) method of breaking it and had noted that all the numbers in the codebook were divisible by three. "Breaking" rather than "solving" a code involves learning enough code words and indicators so that any given message can be read. In particular, JN-25 was significantly changed on 1 December 1940 (JN25a); and again on 4 December 1941 (JN25b), just before the
attack on Pearl Harbor The attack on Pearl HarborAlso known as the Battle of Pearl Harbor was a surprise military strike by the Empire of Japan on the United States Pacific Fleet at Naval Station Pearl Harbor, its naval base at Pearl Harbor on Oahu, Territory of ...
. British, Australian, Dutch and American cryptanalysts co-operated on breaking JN-25 well before the Pearl Harbor attack, but because the Japanese Navy was not engaged in significant battle operations before then, there was little traffic available to use as raw material. Before then, IJN discussions and orders could generally travel by routes more secure than broadcast, such as courier or direct delivery by an IJN vessel. Publicly available accounts differ, but the most credible agree that the JN-25 version in use before December 1941 was not more than perhaps 10% broken at the time of the attack, and that primarily in stripping away its super-encipherment. JN-25 traffic increased immensely with the outbreak of naval warfare at the end of 1941 and provided the cryptographic "depth" needed to succeed in substantially breaking the existing and subsequent versions of JN-25. The American effort was directed from Washington, D.C. by the U.S. Navy's signals intelligence command,
OP-20-G OP-20-G or "Office of Chief Of Naval Operations (OPNAV), 20th Division of the Office of Naval Communications, G Section / Communications Security", was the U.S. Navy's signals intelligence and cryptanalysis group during World War II. Its mission ...
; at Pearl Harbor it was centered at the Navy's Combat Intelligence Unit (
Station HYPO Station HYPO, also known as Fleet Radio Unit Pacific (FRUPAC), was the United States Navy signals monitoring and cryptographic intelligence unit in Hawaii during World War II. It was one of two major Allied signals intelligence units, called Fl ...
, also known as COM 14), led by Commander
Joseph Rochefort Joseph John Rochefort (May 12, 1900 – July 20, 1976) was an American naval officer and cryptanalyst. He was a major figure in the United States Navy's cryptographic and intelligence operations from 1925 to 1946, particularly in the Battle of M ...
. However, in 1942 not every cryptogram was decoded, as Japanese traffic was too heavy for the undermanned Combat Intelligence Unit. With the assistance of ''
Station CAST Station CAST was the United States Navy signals monitoring and cryptographic intelligence fleet radio unit at Cavite Navy Yard in the Philippines, until Cavite was captured by the Japanese forces in 1942, during World War II. It was an important ...
'' (also known as COM 16, jointly commanded by Lts Rudolph Fabian and John Lietwiler) in the Philippines, and the British
Far East Combined Bureau The Far East Combined Bureau, an outstation of the British Government Code and Cypher School, was set up in Hong Kong in March 1935, to monitor Japanese, and also Chinese and Russian (Soviet) intelligence and radio traffic. Later it moved to Sing ...
in Singapore, and using a
punched card A punched card (also punch card or punched-card) is a stiff paper-based medium used to store digital information via the presence or absence of holes in predefined positions. Developed over the 18th to 20th centuries, punched cards were widel ...
tabulating machine The tabulating machine was an electromechanical machine designed to assist in summarizing information stored on punched cards. Invented by Herman Hollerith, the machine was developed to help process data for the U.S. Census, 1890, 1890 U.S. Cens ...
manufactured by
International Business Machines International Business Machines Corporation (using the trademark IBM), nicknamed Big Blue, is an American Multinational corporation, multinational technology company headquartered in Armonk, New York, and present in over 175 countries. It is ...
, a successful attack was mounted against the 4 December 1941 edition (JN25b). Together they made considerable progress by early 1942. "Cribs" exploited common formalities in Japanese messages, such as "I have the honor to inform your excellency" (see
known plaintext attack The known-plaintext attack (KPA) is an attack model for cryptanalysis where the attacker has access to both the plaintext (called a crib) and its encrypted version (ciphertext). These can be used to reveal secret keys and code books. The term "cr ...
). Later versions of JN-25 were introduced: JN-25c from 28 May 1942, deferred from 1 April then 1 May; providing details of the attacks on Midway and Port Moresby. JN-25d was introduced from 1 April 1943, and while the additive had been changed, large portions had been recovered two weeks later, which provided details of Yamamoto's plans that were used in
Operation Vengeance Operation Vengeance was the American military operation to kill Admiral Isoroku Yamamoto of the Imperial Japanese Navy on 18 April 1943 during the Solomon Islands campaign in the Pacific Theater of World War II. Yamamoto, commander of the Combine ...
, the shooting-down of his plane.


JN-39

This was a naval code used by merchant ships (commonly known as the " ''maru'' code"), broken in May 1940. 28 May 1941, when the
whale Whales are a widely distributed and diverse group of fully Aquatic animal, aquatic placental mammal, placental marine mammals. As an informal and Colloquialism, colloquial grouping, they correspond to large members of the infraorder Cetacea ...
factory ship A factory ship, also known as a fish processing vessel, is a large ocean-going vessel with extensive on-board facilities for processing and freezing caught fish or whales. Modern factory ships are automated and enlarged versions of the earlier ...
'' Nisshin Maru No. 2 (1937)'' visited San Francisco,
U.S. Customs Service The United States Customs Service was a federal law enforcement agency of the U.S. federal government. Established on July 31, 1789, it collected import tariffs, performed other selected border security duties, as well as conducted criminal i ...
Agent George Muller and Commander R. P. McCullough of the U.S. Navy's
12th Naval District United States Naval Districts is a system created by the United States Navy to organize military facilities, numbered sequentially by geographic region, for the operational and administrative control of naval bases and shore commands in the Unit ...
(responsible for the area) boarded her and seized her codebooks, without informing
Office of Naval Intelligence The Office of Naval Intelligence (ONI) is the military intelligence agency of the United States Navy. Established in 1882 primarily to advance the Navy's modernization efforts, it is the oldest member of the U.S. Intelligence Community and serv ...
(ONI). Copies were made, clumsily, and the originals returned.Farago, Ladislas. ''The Broken Seal'' (New York: Bantam, 1968), pp.393–395. The Japanese quickly realized JN-39 was compromised, and replaced it with JN-40.


JN-40

JN-40 was originally believed to be a code super-enciphered with a numerical additive, in the same way as JN-25. However, in September 1942, an error by the Japanese gave clues to John MacInnes and Brian Townend, codebreakers at the British
FECB The Far East Combined Bureau, an outstation of the British Government Code and Cypher School, was set up in Hong Kong in March 1935, to monitor Japanese, and also Chinese and Russian (Soviet) intelligence and radio traffic. Later it moved to Sing ...
,
Kilindini Kilindini Harbour is a large, natural deep-water inlet extending inland from Mombasa, Kenya. It is at its deepest center, although the controlling depth is the outer channel in the port approaches with a dredged depth of . It serves as the harbo ...
. It was a fractionating transposition cipher based on a substitution table of 100 groups of two figures each followed by a columnar transposition. By November 1942, they were able to read all previous traffic and break each message as they received it. Enemy shipping, including troop convoys, was thus trackable, exposing it to Allied attack. Over the next two weeks they broke two more systems, the "previously impenetrable" JN167 and JN152.


JN-147

The "minor operations code" often contained useful information on minor troop movements.


JN-152

A simple transposition and substitution cipher used for broadcasting navigation warnings. In 1942 after breaking JN-40 the FECB at Kilindini broke JN-152 and the previously impenetrable JN-167, another merchant shipping cypher.


JN-167

A merchant-shipping cipher (see JN-152).


''Chicago Tribune'' incident

In June 1942 the ''
Chicago Tribune The ''Chicago Tribune'' is an American daily newspaper based in Chicago, Illinois, United States. Founded in 1847, it was formerly self-styled as the "World's Greatest Newspaper", a slogan from which its once integrated WGN (AM), WGN radio and ...
'', run by
isolationist Isolationism is a term used to refer to a political philosophy advocating a foreign policy that opposes involvement in the political affairs, and especially the wars, of other countries. Thus, isolationism fundamentally advocates neutrality an ...
Col. Robert R. McCormick, published an article implying that the United States had broken the Japanese codes, saying the U.S. Navy knew in advance about the Japanese attack on Midway Island, and published dispositions of the Japanese invasion fleet. The executive officer of ''Lexington'', Commander
Morton T. Seligman Morton T. Seligman (July 1, 1895 – July 9, 1967) was an American naval aviator. A two-time recipient of the Navy Cross, Seligman was involved in a security breach in 1942 which brought to an end his promising naval career and forced his reti ...
(who was transferred to shore duties), had shown Nimitz's executive order to reporter
Stanley Johnston Stanley Johnston (1900 – September 13, 1962) was an Australian-American journalist who, as a correspondent during World War II, wrote a Japanese naval codes#Chicago Tribune incident, story for the ''Chicago Tribune'' that inadvertently rev ...
. The government at first wanted to prosecute the ''Tribune'' under the
Espionage Act of 1917 The Espionage Act of 1917 is a United States federal law enacted on June 15, 1917, shortly after the United States entered World War I. It has been amended numerous times over the years. It was originally found in Title 50 of the U.S. Code ( ...
. For various reasons, including the desire not to bring more attention to the article and because the Espionage Act did not cover ''enemy'' secrets, the charges were dropped. A grand jury investigation did not result in prosecution but generated further publicity and, according to
Walter Winchell Walter Winchell (April 7, 1897 – February 20, 1972) was a syndicated American newspaper gossip columnist and radio news commentator. Originally a vaudeville performer, Winchell began his newspaper career as a Broadway reporter, critic and c ...
, "tossed security out of the window". Several in Britain believed that their worst fears about American security were realized. In early August, a RAN intercept unit in Melbourne (
FRUMEL 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 ...
) heard Japanese messages, using a superseded lower-grade code. Changes were made to codebooks and the call-sign system, starting with the new JN-25c codebook (issued two months before). However the changes indicated the Japanese believed the Allies had worked out the fleet details from traffic analysis or had obtained a codebook and additive tables, being reluctant to believe that anyone could have broken their codes (least of all a Westerner).


References


Sources

* * * * * * * *


External links


Bletchley Park - Japanese CodesVideo interview with one of Rochefort's JN-25 codebreaking team
{{DEFAULTSORT:Japanese Naval Codes Imperial Japanese Navy History of cryptography Japan–United States relations World War II Japanese cryptography Intelligence operations Pacific War