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 in 1942 (by breaking code JN-25b) and the shooting down of Japanese admiral Isoroku Yamamoto a year later in Operation Vengeance.
The Imperial Japanese Navy (IJN) used many codes and ciphers. All of these cryptosystems were known differently by different organizations; the names listed below are those given by Western cryptanalytic operations.
The Red Book code was an IJN code book system used in World War I and after. It was called "Red Book" because the American photographs made of it were bound in red covers. 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 was able to break the additive portion of the code.
Knowledge of the Red Book code helped crack the similarly constructed Blue Book code.
A cipher machine developed for Japanese naval attaché ciphers, similar to JADE. It was not used extensively, but Vice Admiral Katsuo Abe, 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."
A cipher machine used by the Imperial Japanese Navy from late 1942 to 1944 and similar to CORAL; see JADE (cypher machine).
A succession of codes used to communicate between Japanese naval installations.
This page is automatically generated and may contain information that is not correct, complete, up-to-date, or relevant to your search query. The same applies to every other page on this website. Please make sure to verify the information with EPFL's official sources.
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 further secret information such as secret keys and code books. The term "crib" originated at Bletchley Park, the British World War II decryption operation, where it was defined as:A plain language (or code) passage of any length, usually obtained by solving one or more cipher or code messages, and occurring or believed likely to occur in a different cipher or code message, which it may provide a means of solving.
The Battle of Midway was a major naval battle in the Pacific Theater of World War II that took place 4–7 June 1942, six months after the Empire of Japan's attack on Pearl Harbor and one month after the Battle of the Coral Sea. The U.S. Navy under Admirals Chester W. Nimitz, Frank J. Fletcher, and Raymond A. Spruance defeated an attacking fleet of the Imperial Japanese Navy under Admirals Isoroku Yamamoto, Chūichi Nagumo, and Nobutake Kondō north of Midway Atoll, inflicting devastating damage on the Japanese fleet.