Purple cipher

Purple cipher is a complex cryptographic system used by the Imperial Japanese Navy during World War II, and was a major focus of cryptanalysis efforts by the United States Navy's OP-20-G and the British Government Code and Cypher School at Bletchley Park. The Purple cipher was used for diplomatic communications between Tokyo and Japanese embassies around the world, including those in Berlin, Rome, and Washington, D.C.. It was also used by the Japanese Foreign Ministry to communicate with Japanese ambassadors such as Kichisaburō Nomura and Hiroshi Ōshima.

Introduction

The Purple cipher was a polyalphabetic substitution cipher, similar to the Enigma machine used by Nazi Germany, but it used a different mechanism to scramble the plaintext. The cipher was used to protect sensitive information such as military operations and diplomatic communications between Japan and its allies, including Germany and Italy. The National Security Agency (NSA) and the Government Communications Headquarters (GCHQ) have studied the Purple cipher, and it has been the subject of research by cryptographers such as William Friedman and Frank Rowlett, who worked at the National Cryptologic Museum.

History

The Purple cipher was developed in the 1930s by the Japanese Navy's cryptographic unit, which was led by Kazuo Ōshima and Masaji Nishihara. The cipher was first used in 1939, and it was used extensively during World War II for communications between Tokyo and Japanese naval bases in China, Southeast Asia, and the Pacific Ocean. The Allies were aware of the existence of the Purple cipher, and they made significant efforts to cryptanalyze it, including the work of codebreakers such as Alan Turing and Gordon Welchman at Bletchley Park, and Joseph Rochefort and Agnes Meyer Driscoll at Pearl Harbor.

Mechanism

The Purple cipher used a complex system of rotors and substitution tables to scramble the plaintext. The cipher consisted of a series of electromechanical machines, including the Type 97 cipher machine, which was used by the Japanese Army, and the Type 91 cipher machine, which was used by the Japanese Navy. The machines used a combination of rotors and wiring to substitute each plaintext letter with a different letter, and the resulting ciphertext was then transmitted over radio or telegraph channels to the intended recipient, who used a similar machine to decrypt the message. The National Institute of Standards and Technology (NIST) and the Institute of Electrical and Electronics Engineers (IEEE) have studied the mechanism of the Purple cipher, and it has been compared to other cryptographic systems, such as the AES and the RSA.

Cryptanalysis

The Purple cipher was cryptanalyzed by the Allies during World War II, and the effort to break the cipher was led by codebreakers such as William Friedman and Frank Rowlett, who worked at the National Cryptologic Museum. The cryptanalysis of the Purple cipher involved a combination of traffic analysis, frequency analysis, and machine cryptanalysis, and it was facilitated by the work of codebreakers such as Alan Turing and Gordon Welchman at Bletchley Park, and Joseph Rochefort and Agnes Meyer Driscoll at Pearl Harbor. The NSA and the GCHQ have studied the cryptanalysis of the Purple cipher, and it has been the subject of research by cryptographers such as Whitfield Diffie and Martin Hellman, who developed the Diffie-Hellman key exchange.

Usage

The Purple cipher was used extensively by the Japanese Navy and the Japanese Foreign Ministry during World War II, and it was used to protect sensitive information such as military operations and diplomatic communications. The cipher was used for communications between Tokyo and Japanese embassies around the world, including those in Berlin, Rome, and Washington, D.C., and it was also used by the Japanese Navy to communicate with its allies, including Germany and Italy. The National Archives and Records Administration (NARA) and the Library of Congress have preserved documents related to the Purple cipher, and it has been the subject of research by historians such as Gar Alperovitz and Robert Butow, who have studied the history of Japan and the history of World War II. Category:Cryptography