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

Gronsfeld Cipher - dCode

Tag(s) : Poly-Alphabetic Cipher

dCode is free and its tools are a valuable help in games, maths, geocaching, puzzles and problems to solve every day!

A suggestion ? a feedback ? a bug ? an idea ? *Write to dCode*!

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:__ The message to be encrypted `GRONSFELD` with the key `1234`. 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`.

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

__Example:__ 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`.

The message has an index of coincidence of about 0.04 to 0.05 (similar to Vigenere).

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 (each character of the key has only 10 possibilities against 26 with Vigenere).

Gronsfeld variants are the same as Vigenere variants.

dCode retains ownership of the "Gronsfeld Cipher" source code. Except explicit open source licence (indicated Creative Commons / free), the "Gronsfeld Cipher" algorithm, the applet or snippet (converter, solver, encryption / decryption, encoding / decoding, ciphering / deciphering, breaker, translator), or the "Gronsfeld Cipher" functions (calculate, convert, solve, decrypt / encrypt, decipher / cipher, decode / encode, translate) written in any informatic language (Python, Java, PHP, C#, Javascript, Matlab, etc.) and all data download, script, or API access for "Gronsfeld Cipher" are not public, same for offline use on PC, mobile, tablet, iPhone or Android app!

Reminder : dCode is free to use.

The copy-paste of the page "Gronsfeld Cipher" or any of its results, is allowed (even for commercial purposes) as long as you cite dCode!

Exporting results as a .csv or .txt file is free by clicking on the *export* icon

Cite as source (bibliography):

*Gronsfeld Cipher* on dCode.fr [online website], retrieved on 2023-12-06,

gronsfeld,vigenere,variant,shift,number,key

https://www.dcode.fr/gronsfeld-cipher

© 2023 dCode — The ultimate 'toolkit' to solve every games / riddles / geocaching / CTF.

Feedback