Gronsfeld Cipher — Free Online Tool

Encrypt and decrypt with the Gronsfeld cipher using a numeric digit key. Gronsfeld Cipher is a free online tool from the ToolsRift Text Encoding Tools collection. It runs entirely in your browser — nothing to install, no signup, and your data never leaves your device.

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How to use Gronsfeld Cipher

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Enter or upload your input. Everything is processed locally on your device.
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Frequently asked questions

What is the Gronsfeld cipher?

A variant of the Vigenère cipher that uses a key made of digits (0–9) instead of letters. Each digit shifts the corresponding letter forward by that many positions.

What is a valid key?

Any string of digits, such as '31415'. The key repeats across the message. Non-digit characters in the key are ignored.

How is 'PROCEED' encrypted with key 31415?

P+3=S, R+1=S, O+4=S, C+1=D, E+5=J, E+3=H, D+1=E, giving 'SSSDJHE'. Decoding with the same key reverses each shift.

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