History of cryptography

The history of cryptography traces how people developed methods to conceal messages, verify their authenticity, and break their protection across civilizations and eras.

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Substitution cipher: A cipher that replaces each plaintext symbol with another symbol according to a rule or key. Monoalphabetic substitution shaped early secret writing and gave codebreakers recurring letter patterns to exploit.
Mesopotamian cuneiform: A writing system used in ancient Mesopotamia, impressed into clay tablets with a reed stylus. Some early cryptographic techniques appear in cuneiform records from Mesopotamia.
Leon Battista Alberti: An Italian Renaissance humanist who described a cipher disk and helped develop polyalphabetic encryption. His rotating cipher disk offered a practical way to vary substitution alphabets within a message.
Black Chamber: A United States cryptanalytic organization that operated from 1919 to 1929 and intercepted foreign diplomatic communications. Its exploitation of diplomatic telegrams exposed the political costs of codebreaking and intelligence sharing.
Steganography: The practice of hiding the existence of a message within an ordinary-looking medium. Cryptography disguises a message’s meaning; steganography aims to conceal that a message exists.
Vigenère cipher: A polyalphabetic substitution cipher that uses a repeating key to select among multiple substitution alphabets. Its long-standing reputation for resisting frequency analysis marked a major step beyond simple substitution.
Scytale: A device associated with ancient Sparta in which a strip of material is wrapped around a rod to encode a message. The scytale became a famous early example of transposition, though its historical use remains uncertain.
Johannes Trithemius: A German abbot and scholar whose works included influential methods for encoding messages. His writings helped circulate systematic cipher techniques in Renaissance Europe.
Zimmermann Telegram: A 1917 German diplomatic message proposing a wartime alliance with Mexico against the United States. British cryptanalysis of the telegram helped bring the United States closer to entering World War I.
One-time pad: A cipher using a truly random key as long as the message, used only once and kept secret. It provides perfect secrecy under strict conditions, unlike historical ciphers vulnerable to statistical attack.