Note the vital distinction: the plaintext is encrypted using itself (shifted backward) as the key.

In a standard Vigenère cipher, a keyword (e.g., "KING") is repeated to match the length of the plaintext:

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Note the vital distinction: the plaintext is encrypted using itself (shifted backward) as the key.

In a standard Vigenère cipher, a keyword (e.g., "KING") is repeated to match the length of the plaintext: auto-key crack only