PURPLE

This article is about the Japanese cipher Purple, also known as AN-1. For other Japanese ciphers, such as JN-25
JN-25
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...

, which played a part in the Battle of Midway, see Japanese naval codes.

In the history of cryptography

History of cryptography

The history of cryptography begins thousands of years ago. Until recent decades, it has been the story of what might be called classic cryptography — that is, of methods of encryption that use pen and paper, or perhaps simple mechanical aids...

, 97-shiki ōbun inji-ki (九七式欧文印字機) ("System 97 Printing Machine for European Characters") or Angōki Taipu-B (暗号機タイプB) ("Type B Cipher Machine"), codenamed Purple by the United States, was a diplomatic cryptographic

Cryptography

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

machine used by the Japanese Foreign Office just before and during World War II

World War II

World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...

. The machine was an electromechanical stepping-switch

Stepping switch

In electrical controls, a stepping switch, also known as a stepping relay, is an electromechanical device which allows an input connection to be connected to one of a number of possible output connections, under the control of a series of electrical pulses. It can step on one axis , or on two axes...

device.

The information gained from decryptions was eventually code-named Magic
Magic (cryptography)
Magic was an Allied cryptanalysis project during World War II. It involved the United States Army's Signals Intelligence Section and the United States Navy's Communication Special Unit. -Codebreaking:...

within the US government.

The codename "Purple" referred to binders used by US cryptanalysts for material produced by various systems; it replaced the Red

Red (cipher machine)

In the history of cryptography, 91-shiki injiki or Angōki Taipu-A , codenamed Red by the United States, was a diplomatic cryptographic machine used by the Japanese Foreign Office before and during World War II. A relatively simple device, it was quickly broken by western cryptographers...

machine used by the Japanese Foreign Office. The Japanese also used CORAL

Coral

Corals are marine animals in class Anthozoa of phylum Cnidaria typically living in compact colonies of many identical individual "polyps". The group includes the important reef builders that inhabit tropical oceans and secrete calcium carbonate to form a hard skeleton.A coral "head" is a colony of...

and JADE

JADE

JADE was the codename given by US codebreakers to a Japanese World War II cipher machine. The Imperial Japanese Navy used the machine for communications from late 1942 until 1944...

stepping-switch systems.

Overview

The Japanese Navy did not cooperate with the Army in cipher machine development, continuing to the war. The Navy believed the Purple machine was sufficiently difficult to break that it did not attempt to revise it to improve security. This seems to have been on the advice of a mathematician, Teiji Takagi

Teiji Takagi

Teiji Takagi was a Japanese mathematician, best known for proving the Takagi existence theorem in class field theory....

(高木　貞治) who lacked a background in cryptanalysis. The Ministry of Foreign Affairs was supplied Red and Purple by the Navy. No one noticed weak points in both machines.

Just before the end of the war, the Army warned the Navy of a weak point of Purple, but the Navy failed to act on this advice.

The Army developed their own cipher machines on the same principle as Enigma

Enigma machine

An Enigma machine is any of a family of related electro-mechanical rotor cipher machines used for the encryption and decryption of secret messages. Enigma was invented by German engineer Arthur Scherbius at the end of World War I...

, 92-shiki injiki (九二式印字機), 97-shiki injiki (九七式印字機) and 1-shiki 1-go injiki(一式一号印字機) from 1932 to 1941. The Army judged that these machines had lower security than the Navy's Purple design, so the Army's two cipher machines were less used.

Prototype of Red

Japanese diplomatic communications at negotiations for the Washington Naval Treaty

Washington Naval Treaty

The Washington Naval Treaty, also known as the Five-Power Treaty, was an attempt to cap and limit, and "prevent 'further' costly escalation" of the naval arms race that had begun after World War I between various International powers, each of which had significant naval fleets. The treaty was...

were broken by the American Black Chamber

Black Chamber

The Cipher Bureau otherwise known as The Black Chamber was the United States' first peacetime cryptanalytic organization, and a forerunner of the National Security Agency...

in 1922, and when this became publicly known, there was considerable pressure to improve their security. In any case, the Japanese Navy had planned to develop their first cipher machine for the following London Naval Treaty

London Naval Treaty

The London Naval Treaty was an agreement between the United Kingdom, the Empire of Japan, France, Italy and the United States, signed on April 22, 1930, which regulated submarine warfare and limited naval shipbuilding. Ratifications were exchanged in London on October 27, 1930, and the treaty went...

. Japanese Navy Captain Risaburo Ito (伊藤利三郎), of Section 10 (cipher & code) of the Japanese Navy General Staff Office, supervised the work.

The development of the machine was the responsibility of the Japanese Navy Institute of Technology, Electric Research Department, Section 6. In 1928, the chief designer Kazuo Tanabe (田辺一雄) and Navy Commander, Genichiro Kakimoto (柿本権一郎) developed a prototype of Red, Ō-bun taipuraita-shiki angō-ki (欧文タイプライタ暗号機) ("Roman-typewriter cipher machine").

The prototype used the same principle as the Kryha

Kryha

In the history of cryptography, the Kryha machine was a device for encryption and decryption, appearing in the early 1920s and used until the 1950s. The machine was the invention of Alexander von Kryha . During the Second World War, Kryha worked as an officer for the German Wehrmacht...

cipher machine, having a plug-board, and was used by the Japanese Navy and Ministry of Foreign Affairs at negotiations for the London Naval Treaty

London Naval Treaty

in 1930.

Red

The prototype machine was finally completed as 91-shiki injiki(九一式印字機) ("Type 91 print machine") in 1931. The year 1931 was year 2591 in the Japanese Imperial calendar. Thus it was prefixed "91-shiki" from the year it was developed.

The 91-shiki injiki Roman-letter model was also used by the Ministry of Foreign Affairs as Angooki Taipu-A (暗号機タイプA) ("Type A Cipher Machine"), codenamed Red by United States cryptanalysts.

The Red machine was unreliable unless the contacts in its half-rotor switch were cleaned every day. It enciphered vowels (AEIOUY) and consonants separately, perhaps to reduce telegram costs, and this was a significant weak point. The Navy also used the 91-shiki injiki Kana

Kana

Kana are the syllabic Japanese scripts, as opposed to the logographic Chinese characters known in Japan as kanji and the Roman alphabet known as rōmaji...

-letter model at its bases and on its vessels.

In 1937, the next generation 97-shiki injiki(九七式印字機) ("Type 97 print machine") was completed. The Ministry of Foreign Affairs machine was the Angooki Taipu-B (暗号機タイプB) ("Type B Cipher Machine"), codenamed Purple by United States cryptanalysts.

The chief designer of Purple was Kazuo Tanabe (田辺一雄). His engineers were Masaji Yamamoto (山本正治) and Eikichi Suzuki (鈴木恵吉). Eikichi Suzuki suggested use of stepping switch

Stepping switch

instead of the more troublesome half-rotor switch.

Clearly, the Purple machine was more secure than Red, but the Navy did not recognize that Red had already been broken. The Purple machine inherited a weakness from the Red machine that six letters of the alphabet were encrypted separately. It differed from RED in that the group of letters was changed and announced every nine days, whereas in RED they were permanently fixed as the English vowels 'a', 'e', 'i', 'o', 'u' and 'y'. This US Army SIS

Signals Intelligence Service

The Signals Intelligence Service was the United States Army codebreaking division, headquartered at Arlington Hall. It was a part of the Signal Corps so secret that outside the office of the Chief Signal officer, it did not officially exist. William Friedman began the division with three "junior...

was able to break the cipher used for the six letters before it was able to break the one used for the 20 others.

Weaknesses and cryptanalysis

In operation, the enciphering machine accepted typewritten input (in Latin letters) and produced ciphertext output, and vice versa when deciphering messages. The result was a potentially excellent cryptosystem. In fact, operational errors, chiefly in key

Key (cryptography)

In cryptography, a key is a piece of information that determines the functional output of a cryptographic algorithm or cipher. Without a key, the algorithm would produce no useful result. In encryption, a key specifies the particular transformation of plaintext into ciphertext, or vice versa...

choice, made the system less secure than it could have been; in that way the Purple code shared the fate of the German Enigma machine

Enigma machine

. The cipher was broken by a team from the US Army Signals Intelligence Service, then directed by William Friedman in 1940. Reconstruction of the Purple machine was based on ideas of Larry Clark. Advances into the understanding of Purple keying procedures were made by Lt Francis A. Raven, USN. Raven discovered that the Japanese had divided the month into three 10-days periods, and within each period they used the keys of the first day with small predictable changes.

The Japanese believed it to be unbreakable throughout the war, and even for some time after the war, even though they had been informed otherwise by the Germans. In April 1941, Hans Thomsen

Hans Thomsen

Hans Thomsen was a German diplomat for the Third Reich. He served as Chargé d'Affaires at the Embassy of Germany in Washington, representing the German government from November 1938 to December 11, 1941...

, a diplomat at the German embassy in Washington, D.C., sent a message to Joachim von Ribbentrop

Joachim von Ribbentrop

Ulrich Friedrich Wilhelm Joachim von Ribbentrop was Foreign Minister of Germany from 1938 until 1945. He was later hanged for war crimes after the Nuremberg Trials.-Early life:...

, the German foreign minister, informing him that "an absolutely reliable source" had told Thomsen that the Americans had broken the Japanese diplomatic cipher (that is, Purple). That source apparently was Konstantin Umansky

Konstantin Umansky

Konstantin Aleksandrovich Umansky , was a Soviet diplomat, editor, journalist and artist.-Biography:Umansky, who was Jewish, was born in Mykolaiv; he began studies at Moscow University in 1918, and joined the Russian Communist Party in 1919....

, the Soviet ambassador to the US, who had deduced the leak based upon communications from Sumner Welles

Sumner Welles

Benjamin Sumner Welles was an American government official and diplomat in the Foreign Service. He was a major foreign policy adviser to President Franklin D. Roosevelt and served as Under Secretary of State from 1937 to 1943, during FDR's presidency.-Early life:Benjamin Sumner Welles was born in...

. The message was duly forwarded to the Japanese; but use of the code continued.

The United States obtained portions of a Purple machine from the Japanese Embassy in Germany following Germany's defeat in 1945 (see image above) and discovered that the Japanese had used precisely the same "stepping switch" in its construction that Leo Rosen

Leo Rosen

Leo Rosen was a U.S. cryptanalyst who worked with Frank Rowlett at Signals Intelligence Service before the start of World War II on Japanese ciphers. Rowlett found a method to read the messages enciphered on the Japanese PURPLE machine...

of SIS had chosen when building a "duplicate" (or Purple analog machine) in Washington in 1939 and 1940. The "stepping switch" was a common type of unit used in high-tech telephone exchange

Telephone exchange

In the field of telecommunications, a telephone exchange or telephone switch is a system of electronic components that connects telephone calls...

s in countries like the United States, Canada, the UK and Japan, that had good dial-telephone systems in their large cities. These fast switches were at the heart of the systems.

Apparently, all of the other Purple machines at Japanese embassies and consulates around the world (e.g. in Axis countries, Washington, London, Moscow, and in neutral countries) and in Japan itself, were destroyed and ground into particles by the Japanese. American occupation troops in Japan in 1945-52 searched for any remaining units.

The Purple machine itself was first used by Japan in June 1938, but U.S. and British cryptanalysts had broken some of its messages well before the attack on Pearl Harbor

Attack on Pearl Harbor

The attack on Pearl Harbor was a surprise military strike conducted by the Imperial Japanese Navy against the United States naval base at Pearl Harbor, Hawaii, on the morning of December 7, 1941...

. U.S. cryptanalysts decrypted and translated Japan's 14-part message to its Washington Embassy (ominously) breaking off negotiations with the United States at 1 p.m. Washington time on 7 December 1941, before the Japanese Embassy in Washington had done so. Decryption and typing difficulties at the Embassy, coupled with ignorance of the importance of it being on time, were major reasons the Nomura note" was delivered late.

Other factors

During World War II, the Japanese embassy in Nazi Germany

Nazi Germany

Nazi Germany , also known as the Third Reich , but officially called German Reich from 1933 to 1943 and Greater German Reich from 26 June 1943 onward, is the name commonly used to refer to the state of Germany from 1933 to 1945, when it was a totalitarian dictatorship ruled by...

was kept well-informed on German military affairs. This information was reported to Tokyo in Purple-enciphered radio messags. These reports included, for example, details of the Atlantic Wall

Atlantic Wall

The Atlantic Wall was an extensive system of coastal fortifications built by Nazi Germany between 1942 and 1944 along the western coast of Europe as a defense against an anticipated Allied invasion of the mainland continent from Great Britain.-History:On March 23, 1942 Führer Directive Number 40...

fortifications along the coasts of France and Belgium. Since these messages were being read by the Allies, this provided valuable intelligence about German military preparations against the forthcoming invasion of Western Europe.

The decrypted Purple traffic, and Japanese messages generally, was the subject of acrimonious hearings in Congress post-World War II in connection with an attempt to decide who, if anyone, had allowed the attack at Pearl Harbor to happen and who therefore should be blamed. It was during those hearings that the Japanese learned, for the first time, that the Purple cipher machine had indeed been broken.

External links

The Purple Machine Information and a simulator (for Windows).
Purple, Coral, and Jade (Original link dead as of Wayback Machine crawl 10 October 2009)

The source of this article is wikipedia, the free encyclopedia. The text of this article is licensed under the GFDL.

Overview

Prototype of Red

Red

Purple

Weaknesses and cryptanalysis

Other factors

Further reading

External links