The Alphabet Cipher
1868 study by Lewis Carroll
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"The Alphabet Cipher" was a brief study published by Lewis Carroll in 1868, describing how to use the alphabet to send encrypted codes.[1] It was one of four ciphers he invented between 1858 and 1868, and one of two polyalphabetic ciphers he devised during that period and used to write letters to his friends.[2]
It describes what is known as a Vigenère cipher, a well-known scheme in cryptography. While Carroll calls this cipher "unbreakable", Friedrich Kasiski had already published in 1863 a volume describing how to break such ciphers and Charles Babbage had secretly found ways to break polyalphabetic ciphers in the previous decade during the Crimean War.
