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Era used: Ancient Greece; Significance: One of the earliest known ciphers, used by the Spartans for military messaging.

Era used: Modern; Significance: A public-key cryptosystem widely used for secure data transmission.

Era used: World War II; Significance: Used by the Japanese Foreign Office; breaking this code aided the US in the war effort.

Era used: Roman Era; Significance: Used by Julius Caesar to encode military messages.

Era used: World War II; Significance: Native American languages used to create an unbreakable code used in the Pacific Theater.

Era used: Invented in the late 18th Century; Significance: Though not used significantly in its time, it was later reinvented and used as the M-94 cipher device by the US military.

Era used: World War II; Significance: A German cipher machine producing a Vernam stream cipher, it was used for high-level Army communications.

Era used: World War II; Significance: An advanced American cipher machine that remained unbroken throughout the war.

Era used: Renaissance Period; Significance: Provided a way to create a more secure cipher using a keyword.

Era used: Used in various forms since the Renaissance; Significance: Utilizes a shared secret text to encode messages where the key is a page, line and word number.

Era used: Modern Era (Installed in 1990); Significance: A sculpture located at the CIA headquarters containing four encrypted messages.

Era used: Developed in the Renaissance, used through World War II; Significance: A transposition cipher that writes the message in columns before permuting them.

Era used: World War II; Significance: Germans used this to encrypt military communications; cracking this code helped the Allies win the war.

Era used: Ancient Hebrew; Significance: One of the oldest known ciphers, it substitutes the first letter of the Hebrew alphabet for the last, the second for the second to last, and so on.

Era used: Early 17th Century; Significance: A steganographic method devised by Sir Francis Bacon to hide messages within other, non-secret texts.

Era used: Late 1960s - Early 1970s; Significance: A series of complex ciphers sent to newspapers by the Zodiac Killer.

Era used: 20th Century, still used; Significance: An unbreakable cipher when used correctly; has been used for secure government and military communications.

Era used: 15th Century; Significance: Created by Leon Battista Alberti, known as the 'father of Western cryptography', it allowed for a polyalphabetic cipher with a mixed alphabet.

Era used: World War I; Significance: Developed by the German Army and designed to be insusceptible to frequency analysis.