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Gronsfeld Cipher

Tool to decrypt/encrypt using Gronsfeld. Gronsfeld Cipher is a variant of the Vigenère cipher, the difference being that the key is a number.

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Gronsfeld Cipher -

Tag(s) : Cryptography, Vigenere Variant

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# Gronsfeld Cipher

## Gronsfeld Encoder

Tool to decrypt/encrypt using Gronsfeld. Gronsfeld Cipher is a variant of the Vigenère cipher, the difference being that the key is a number.

### How to encrypt using Gronsfeld cipher?

Gronsfeld encryption uses the Vigenere method, the difference being that the key is directly numeric, no need to calculate the rank of the letters of the key in the alphabet. However, the corresponding shifts have to be applied, so the Gronsfeld method approaches a multi-shift encryption.

Example: Consider the message to be encrypted GRONSFELD with the key 1234. You add 1 to G to get H (the letter 1 rank after G is H in the alphabet), then add 2 to C or E (the letter 2 ranks after C is E), and so on.

 Plain letter G R O N S F E L D Key (repeated) 1 2 3 4 1 2 3 4 1 Cipher Letter H T R R T H H P E

Example: The encrypted message is HTRRTHHPE.

### How to decrypt Gronsfeld cipher?

Decryption requires to know the decryption key (and the alphabet used if necessary). The decryption identical to Vigenere, but with a numeric key.

Example: Consider the encrypted message EEREG with the key 123

 Ciphertext Letter E E R E G Key (Repeated) 1 2 3 1 2 Decrypted Letter D C O D E

The plain message is then DCODE.

### How to recognize Gronsfeld ciphertext?

The message has an index of coincidence of about 0.4 to 0.5.

### How to decipher Gronsfeld without key?

Cryptanalysis techniques used for Vigenere are also applicable to Gronsfeld. These techniques also accelerated since the use of a numeric key limits the number of combinations.

### What are the variants of the Gronsfeld cipher?

Gronsfeld variants are the same as Vigenere variants.