The Vigenère cipher is a polyalphabetic substitution cipher that encrypts text by using a repeating keyword to apply a series of different Caesar shifts.
Invented by Italian cryptographer Giovan Battista Bellaso in 1553 (but historically misattributed to French diplomat Blaise de Vigenère), it was famously dubbed “le chiffre indéchiffrable” (the indecipherable cipher) because it resisted standard frequency analysis and remained unbroken for nearly 300 years. How It Works: The Core Concept
Unlike a standard Caesar cipher—which shifts every letter in a message by the exact same number of spaces (e.g., shifting everything by 3)—the Vigenère cipher changes the shift amount for every single letter based on a secret keyword.
Each letter of the alphabet is assigned a numerical value from 0 to 25 (
). The letters of the chosen keyword dictate how many spaces to shift the corresponding message letters. Step-by-Step Encryption
To encrypt a message, you follow a straightforward, repetitive process:
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