Rangdom

Encode text with a numeric key

The Gronsfeld cipher is a Vigenère variant keyed by digits instead of letters. It repeats your numeric key across the message and shifts each letter by the matching digit. Longer, less predictable keys are harder to break than a single Caesar shift.

When to use this tool

Reach for the Gronsfeld cipher when you have a numeric key rather than a keyword — it is a Vigenère variant that shifts each letter by the next digit of the key. It turns up constantly in CTF challenges, puzzle hunts, and escape rooms because the key is just a string of digits. Type a numeric key, then encode or decode on a single page.

Privacy and limitations

Everything runs locally in your browser; nothing is sent anywhere. This is a classical cipher, not real encryption — it only shifts A–Z and a–z, leaves digits and symbols untouched, and offers no auto-solving. You need the exact numeric key to decode a message.

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