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Keyword Shift Cipher

Tool to encrypt a message with a shift according to a keyword. The use of an alphabet shift and the use of a keyword are basic techniques for ciphers, here it is a mixture of these two techniques.

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Keyword Shift Cipher -

Tag(s) : Poly-Alphabetic Cipher

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Keyword Shift Cipher

Vigenere Cipher

The first keyword shift cipher was invented by Blaise de Vigenere. Each letter of the plain message is shifted according to a letter of a keyword.

⮞ Go to: Vigenere Cipher

Shift ciphers

Many variations of word-based offset ciphers can be envisaged. The general principle is to encode the keyword in numbers and to apply the successive offsets according to the obtained numbers.

How to encrypt using a keyword shift cipher?

The principle of keyword-based ciphers is an improvement in shift ciphering. The shift is to replace one letter with another a little further in the alphabet, it is the method of the figure of Caesar. This technique has only 26 choices of offset and is therefore easily breakable.

The use of a key word makes it possible to define several successive different offsets, deduced from the key word itself, by associating with each letter of the key word an offset. This technique takes the name of polyalphabetic cipher.

Example: ABC can correspond to the shifts 1,2,3, associating A = 1, B = 2, C = 3, etc, on the principle of Z = 26.

The Vigenere figure is the first use of this kind of encryption, it associates A = 0, B = 1, etc. Z = 25.

How to decrypt a keyword shift cipher?

Key word-based shift decryption is the inverse shift operation of encryption. If the offset was +N, it will be -N, if it was shifted to the right, it will be shifted to the left.

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