The Caesar cipher is a form of monoalphabetic cipher: a simple substitution algorithm crated by shifting the alphabet over three places. Monoalphabetic ciphers can also utilize a scrambled version of the alphabet. The fundamental principle for these ciphers is that each letter is replaced by another letter consistently throughout the message.
Monoalphabetic ciphers are still driven by the characteristics of plaintext language, making them relatively easy to decipher. Polyalphabetic ciphers are harder to decipher because they use several alphabets for substituting the plaintext. In a polyalphabetic cipher, each letter is substituted by a letter from a different alphabet. Since the number of alphabets are typically limited, they are recycled as the message proceeds.
Blais de Vigenere developed a polyalphabetic cipher using 26 alphabets and a key word. Each alphabet was offset by one space and grouped in a table. The top row represented the plaintext values, while the first column represents the substitution alphabets.
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